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1. United States
Department of
Agriculture
Rural
Utilities
Service
RUS Bulletin
1724E-300
Issued
June 2001
Design Guide for
Rural Substations

2. (BLANK PAGE)

3. UNITED STATES DEPARTMENT OF AGRICULTURE
Rural Utilities Service
RUS BULLETIN 1724E-300
SUBJECT: Design Guide for Rural Substations
TO: All RUS Borrowers
RUS Electric Staff
EFFECTIVE DATE: Date of approval.
OFFICE OF PRIMARY INTEREST: Transmission Branch, Electric Staff Division.
INSTRUCTIONS: This bulletin is an update and revision of previous REA Bulletin 65-1, “Design
Guide for Rural Substations” (revised June 1978). Replace previous Bulletin 65-1 with this bulletin
and file with 7 CFR Part 1724.
AVAILABILITY: This bulletin is available on the Rural Utilities Service website at:
http://www.usda.gov/rus/electric
PURPOSE: This bulletin provides a basic design guide and a reference tool for designing rural
substations.
GENERAL: This Bulletin has been revised to bring the publication up to date with latest industry
standards, current RUS format, and technical requirements.
Our thanks to Cooperative Research Network of the National Rural Electric Cooperative Association,
(NRECA) which has supported this project, and it's consultant Burns & McDonnell Engineering
Company for the work which has made it possible to put this revision of the design guide together.
The following current and former members of the Substation Subcommittee of the (NRECA),
Transmission and Distribution (T&D) Engineering Committee provided invaluable assistance in
preparing this document.
1. Bardwell, Jim, SGS Witter, Inc., Albuquerque, New Mexico
2. Chapman, George, Patterson & Dewar Engineers, Inc., Decatur, Georgia
3. Eskandary, Mike, USDA-RUS-ESD-TB, Washington, DC
4. Howard, Jerrod, Central Electric Power Co-op, Inc., Columbia, SC
5. Kahanek, Bil, Lower Colorado River Authority, Austin, TX
6. Myers, Tom, Berkeley Electric Co-op, Moncks Corner, SC
7. Malone, Ken, Middle Tennessee EMC, Murfreesboro, TN
8. Nicholson, Norris, USDA-RUS-ESD-TB, Washington, DC

5. Bulletin 1724E-300
Page 5
TABLE OF CONTENTS
ABBREVIATIONS AND ACRONYMS..........................................................................................31
CHAPTER 1 - INTRODUCTION....................................................................................................37
1.1 PREFACE........................................................................................................................37
1.2 PURPOSE AND SCOPE.................................................................................................37
1.3 RELATIONSHIP OF SUBSTATION TO OVERALL POWER SYSTEM.........................37
1.4 IMPORTANCE OF ADEQUATE SUBSTATION PLANNING AND
ENGINEERING...............................................................................................................38
1.5 TYPES OF SUBSTATIONS.............................................................................................38
1.5.1 General..............................................................................................................38
1.5.2 Distribution Substations .......................................................................................39
1.5.3 Transmission Substations.....................................................................................39
1.5.4 Switching Substations..........................................................................................39
1.6 REFERENCES.................................................................................................................40
CHAPTER 2 - GENERAL DESIGN CONSIDERATIONS...............................................................41
2.1 INITIAL AND ULTIMATE REQUIREMENTS ...............................................................41
2.2 SITE CONSIDERATIONS...............................................................................................41
2.3 ENVIRONMENTAL CONSIDERATIONS......................................................................42
2.3.1 General..............................................................................................................42
2.3.2 Weather.............................................................................................................46
2.3.3 Altitude ..............................................................................................................46
2.3.4 Earthquakes .......................................................................................................47
2.3.5 Other Considerations...........................................................................................50
2.4 INTERFACING CONSIDERATIONS..............................................................................51
2.4.1 Line Tension.......................................................................................................51
2.5 RELIABILITY CONSIDERATIONS...............................................................................51
2.6 OPERATING CONSIDERATIONS.................................................................................52
2.7 SAFETY CONSIDERATIONS.........................................................................................52
2.8 MAINTENANCE CONSIDERATIONS...........................................................................52
2.9 REFERENCES.................................................................................................................52
CHAPTER 3 - DOCUMENTS.........................................................................................................55
3.1 GENERAL.......................................................................................................................55
3.1.1 Possible Documents or Studies Required of the Engineer.......................................55
3.2 NEED FOR DOCUMENTATION....................................................................................55
3.3 PROCEDURES................................................................................................................56
3.4 PROCUREMENT............................................................................................................56
3.5 DRAWINGS....................................................................................................................57
3.5.1 General..............................................................................................................57
3.5.2 Quality...............................................................................................................57
3.5.3 Types of Drawings .............................................................................................59
3.6 STUDIES.........................................................................................................................71
3.7 REFERENCES.................................................................................................................71

6. Bulletin 1724E-300
Page 6
APPENDIX A—TYPICAL SUBSTATION DRAWING CHECKLIST.......................................73
APPENDIX B—U.S. DEPARTMENT OF AGRICULTURE RURAL UTILITIES
SERVICE SUBSTATION DESIGN SUMMARY.......................................................................91
1 INTRODUCTION...................................................................................................94
2 DESIGN CONSIDERATIONS.................................................................................95
3 DOCUMENTS ........................................................................................................98
4 PHYSICAL LAYOUT........................................................................................... 100
5 MAJOR EQUIPMENT.......................................................................................... 104
6 SITE .................................................................................................................. 107
7 STRUCTURES...................................................................................................... 108
8 FOUNDATIONS................................................................................................... 109
9 GROUNDING....................................................................................................... 109
10 INSULATED CABLES AND RACEWAYS.......................................................... 111
11 CORROSION........................................................................................................ 112
12 PROTECTIVE RELAYING................................................................................... 112
13 INSTRUMENTS, TRANSDUCER, AND METERS ............................................... 114
14 SUBSTATION AUTOMATION............................................................................ 114
15 AC AND DC AUXILIARY SYSTEMS.................................................................. 115
16 CONTROL HOUSE .............................................................................................. 116
17 COMMUNICATIONS........................................................................................... 117
CHAPTER 4 - PHYSICAL LAYOUT ........................................................................................... 119
4.1 INTRODUCTION.......................................................................................................... 119
4.2 LAYOUT CONSIDERATIONS..................................................................................... 119
4.2.1 Initial Design Parameters .................................................................................. 119
4.2.2 Selection of Switching Scheme .......................................................................... 119
4.2.3 Substation Expansion......................................................................................... 119
4.2.4 Substation Profile .............................................................................................. 120
4.2.5 Underground Circuits........................................................................................ 120
4.2.6 Equipment Removal.......................................................................................... 120
4.3 DISTRIBUTION SUBSTATIONS.................................................................................. 121
4.3.1 Basic Distribution Substation.............................................................................. 121
4.3.2 Transformer Primary Protective Devices ........................................................... 122
4.3.3 Voltage Regulation............................................................................................ 122
4.3.4 Circuit Breaker/Recloser Bypass Facilities ......................................................... 123
4.3.5 Surge Arresters................................................................................................ 124
4.3.6 Enclosed Equipment.......................................................................................... 124
4.4 TRANSMISSION SUBSTATIONS................................................................................ 125
4.4.1 Basic Transmission Substation........................................................................... 125
4.4.2 Circuit Breaker Bypass Facilities ....................................................................... 126
4.4.3 Surge Arresters................................................................................................ 126
4.4.4 Carrier Equipment............................................................................................. 127
4.4.5 Voltage Transformers....................................................................................... 127
4.4.6 Current Transformers ....................................................................................... 127
4.4.7 Grounding Switches .......................................................................................... 127
4.5 SWITCHING STATIONS.............................................................................................. 127
4.5.1 Basic Switching Substation................................................................................ 128

7. Bulletin 1724E-300
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4.5.2 Surge Arresters................................................................................................ 128
4.6 TYPICAL BUS CONFIGURATIONS............................................................................ 128
4.6.1 Single Bus ........................................................................................................ 129
4.6.2 Sectionalized Bus.............................................................................................. 132
4.6.3 Main and Transfer Bus ..................................................................................... 133
4.6.4 Ring Bus .......................................................................................................... 136
4.6.5 Breaker-and-a-Half .......................................................................................... 139
4.6.6 Double Breaker–Double Bus............................................................................. 139
4.6.7 Relative Switching Scheme Costs ...................................................................... 141
4.7 PROTECTION OF SUBSTATION INSULATION......................................................... 142
4.7.1 General............................................................................................................ 142
4.7.2 Surge Protection............................................................................................... 142
4.7.3 Direct Stroke Protection.................................................................................... 142
4.8 SUBSTATION INSULATORS....................................................................................... 146
4.8.1 Outdoor Apparatus Insulators............................................................................ 146
4.8.2 Suspension Insulators........................................................................................ 151
4.9 ELECTRICAL CLEARANCES...................................................................................... 153
4.10 BARE CONDUCTORS.................................................................................................. 157
4.10.1 Conductor Materials.......................................................................................... 157
4.10.2 Rigid Conductors .............................................................................................. 157
4.10.3 Flexible Conductors........................................................................................... 159
4.10.4 Conductor Ampacity......................................................................................... 160
4.10.5 Bus Connections............................................................................................... 160
4.11 RIGID BUS DESIGN ..................................................................................................... 163
4.11.1 General Considerations...................................................................................... 163
4.11.2 Procedure for Rigid Bus Design......................................................................... 164
4.11.3 Bus Design Example ......................................................................................... 171
4.12 STRAIN BUS DESIGN.................................................................................................. 176
4.12.1 General Considerations...................................................................................... 176
4.12.2 Procedure for Strain Bus Design........................................................................ 177
4.13 APPLICATION OF MOBILE TRANSFORMERS AND SUBSTATIONS...................... 184
4.13.1 Size and Maneuverability of the Equipment......................................................... 185
4.13.2 Installation Location and Provisions.................................................................... 185
4.13.3 Electrical Clearances ........................................................................................ 185
4.13.4 Primary and Secondary Connections .................................................................. 185
4.13.5 Grounding......................................................................................................... 186
4.13.6 Auxiliary System Requirements ......................................................................... 186
4.13.7 Safety................................................................................................................. 186
4.14 REFERENCES............................................................................................................... 186
4.15 LEGEND FOR EQUATIONS......................................................................................... 188
CHAPTER 5 - MAJOR EQUIPMENT........................................................................................... 191
5.1 GENERAL..................................................................................................................... 191
5.2 POWER TRANSFORMERS .......................................................................................... 191
5.2.1 General............................................................................................................ 191
5.2.2 Types............................................................................................................... 192
5.2.3 Ratings............................................................................................................. 193

8. Bulletin 1724E-300
Page 8
5.2.4 Taps ................................................................................................................ 200
5.2.5 Impedance ....................................................................................................... 201
5.2.6 Phase Relation.................................................................................................. 201
5.2.7 Parallel Operation of Transformers.................................................................... 202
5.2.8 Dielectric Requirements.................................................................................... 204
5.2.9 Short-Circuit Requirements................................................................................ 207
5.2.10 Cooling Equipment............................................................................................ 209
5.2.11 Oil and Oil Preservation Equipment.................................................................... 210
5.2.12 Audible Sound .................................................................................................. 210
5.2.13 Tank................................................................................................................ 214
5.2.14 Accessories...................................................................................................... 214
5.2.15 Electrical Tests and Measurements.................................................................... 214
5.2.16 Shipment.......................................................................................................... 216
5.2.17 Warranty.......................................................................................................... 216
5.2.18 Core and Coils.................................................................................................. 216
5.2.19 Specifications ................................................................................................... 217
5.2.20 References....................................................................................................... 217
5.3 POWER CIRCUIT BREAKERS .................................................................................... 219
5.3.1 General............................................................................................................ 219
5.3.2 Types of Circuit Breakers ................................................................................. 221
5.3.3 Ratings............................................................................................................. 226
5.3.4 Operating Mechanisms...................................................................................... 238
5.3.5 Tests................................................................................................................ 242
5.3.6 Control and Auxiliary Power Requirements ........................................................ 244
5.3.7 Purchase Evaluation.......................................................................................... 244
5.3.8 Shipment and Installation................................................................................... 244
5.3.9 References....................................................................................................... 244
5.4 METAL-CLAD SWITCHGEAR..................................................................................... 245
5.4.1 General............................................................................................................ 245
5.4.2 Types............................................................................................................... 246
5.4.3 Ratings............................................................................................................. 249
5.4.4 Purchase Considerations ................................................................................... 250
5.4.5 References....................................................................................................... 252
5.5 SUBSTATION VOLTAGE REGULATORS................................................................... 252
5.5.1 General............................................................................................................ 252
5.5.2 Types............................................................................................................... 253
5.5.3 Ratings............................................................................................................. 254
5.5.4 Regulator Controls ............................................................................................ 261
5.5.5 Lightning Protection.......................................................................................... 262
5.5.6 References....................................................................................................... 262
5.6 SHUNT CAPACITOR EQUIPMENT ............................................................................ 262
5.6.1 General............................................................................................................ 262
5.6.2 System Considerations ...................................................................................... 263
5.6.3 Types............................................................................................................... 267
5.6.4 Bank Configuration........................................................................................... 268
5.6.5 Ratings............................................................................................................. 269
5.6.6 Switching ......................................................................................................... 271

9. Bulletin 1724E-300
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5.6.7 Protection......................................................................................................... 280
5.6.8 Grounding and Short-Circuiting of Capacitor Banks............................................. 285
5.6.9 Mounting.......................................................................................................... 285
5.6.10 Factory Tests ................................................................................................... 288
5.6.11 Inspection and Maintenance .............................................................................. 288
5.6.12 Typical Technical Specification.......................................................................... 288
5.6.13 References....................................................................................................... 297
5.7 AIR SWITCHES............................................................................................................ 298
5.7.1 General............................................................................................................ 298
5.7.2 Types of Air Switches....................................................................................... 299
5.7.3 Various Constructions of Outdoor Air Switches.................................................. 301
5.7.4 Usual Service Conditions................................................................................... 308
5.7.5 Ratings............................................................................................................. 308
5.7.6 Other Requirements.......................................................................................... 312
5.7.7 Mounting Considerations ................................................................................... 322
5.7.8 References....................................................................................................... 323
5.8 SURGE ARRESTERS.................................................................................................... 323
5.8.1 General............................................................................................................ 323
5.8.2 Classification of Arresters................................................................................. 324
5.8.3 Ratings (Standard Definitions) ........................................................................... 332
5.8.4 System Voltage ................................................................................................ 333
5.8.5 Grounded vs. Ungrounded Systems.................................................................... 333
5.8.6 Application Guide for Silicon-Carbide Valve Arresters ........................................ 334
5.8.7 Application Guide for Metal Oxide Surge Arresters............................................. 342
5.8.8 Location........................................................................................................... 352
5.8.9 Protection at Line Entrances.............................................................................. 356
5.8.10 References....................................................................................................... 357
5.9 AUTOMATIC CIRCUIT RECLOSERS.......................................................................... 357
5.9.1 General............................................................................................................ 357
5.9.2 Recloser Classifying Features............................................................................ 361
5.9.3 Recloser Ratings............................................................................................... 363
5.9.4 Construction..................................................................................................... 371
5.9.5 Recloser Operation........................................................................................... 373
5.9.6 Maintenance and Inspection .............................................................................. 375
5.9.7 Mounting.......................................................................................................... 376
5.9.8 References....................................................................................................... 376
5.10 INSTRUMENT TRANSFORMERS................................................................................ 377
5.10.1 General............................................................................................................ 377
5.10.2 Service Conditions ............................................................................................ 377
5.10.3 Accuracy......................................................................................................... 379
5.10.4 Secondary Burdens........................................................................................... 381
5.10.5 Construction..................................................................................................... 381
5.10.6 Current Transformers ....................................................................................... 382
5.10.7 Voltage Transformers....................................................................................... 389
5.10.8 Combination Units............................................................................................. 398
5.10.9 Tests................................................................................................................ 399
5.10.10 References....................................................................................................... 399

10. Bulletin 1724E-300
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5.11 COUPLING CAPACITORS AND COUPLING CAPACITOR VOLTAGE
TRANSFORMERS......................................................................................................... 400
5.11.1 General............................................................................................................ 400
5.11.2 Coupling Capacitors.......................................................................................... 400
5.11.3 Coupling Capacitor Voltage Transformers.......................................................... 401
5.11.4 Service Conditions ............................................................................................ 404
5.11.5 Ratings............................................................................................................. 404
5.11.6 Tests................................................................................................................ 408
5.11.7 References....................................................................................................... 408
5.12 MOBILE UNITS............................................................................................................ 409
5.12.1 Feasibility......................................................................................................... 409
5.12.2 Mobile Transformers......................................................................................... 409
5.12.3 Mobile Substations ............................................................................................ 410
5.12.4 Phase Rotation Indicators.................................................................................. 410
5.12.5 Other Considerations......................................................................................... 410
5.12.6 Accessories Included with the Mobile Unit ......................................................... 412
CHAPTER 6 - SITE DESIGN ........................................................................................................ 413
6.1 GENERAL..................................................................................................................... 413
6.2 TYPES OF GRADED YARDS....................................................................................... 413
6.2.1 Flat Yards ........................................................................................................ 414
6.2.2 Sloped Yards.................................................................................................... 414
6.2.3 Stepped Yards (Two or More Levels)................................................................ 414
6.3 PRELIMINARY REQUIREMENTS............................................................................... 414
6.4 DRAINAGE CONSIDERATIONS................................................................................. 415
6.4.1 Stormwater Management.................................................................................. 415
6.4.2 Surface Drainage System.................................................................................. 415
6.4.3 Closed Drainage System................................................................................... 415
6.4.4 Planning........................................................................................................... 415
6.4.5 Design ............................................................................................................. 415
6.5 EARTHWORK CONSIDERATIONS AND DESIGN..................................................... 419
6.5.1 Borrow ............................................................................................................ 419
6.5.2 Topsoil............................................................................................................. 419
6.5.3 Cut and Fill....................................................................................................... 421
6.5.4 Compaction...................................................................................................... 421
6.5.5 Cleanup............................................................................................................ 422
6.6 ROADS AND OTHER ACCESS.................................................................................... 422
6.6.1 General Access Roads...................................................................................... 422
6.6.2 Grade............................................................................................................... 422
6.6.3 Curvature......................................................................................................... 422
6.6.4 Design ............................................................................................................. 422
6.6.5 Railroad Spur.................................................................................................... 422
6.6.6 Roadways in the Substation Yard....................................................................... 423
6.7 EROSION PROTECTION ............................................................................................. 423
6.7.1 General............................................................................................................ 423
6.7.2 Legal Requirements.......................................................................................... 423
6.8 YARD SURFACING MATERIAL................................................................................. 423

11. Bulletin 1724E-300
Page 11
6.9 SECURITY FENCE....................................................................................................... 424
6.10 REFERENCES .............................................................................................................. 424
APPENDIX C—SAMPLE SUBSTATION SECURITY FENCE SPECIFICATION.................. 426
CHAPTER 7 - STRUCTURES....................................................................................................... 431
7.1 MATERIALS................................................................................................................. 431
7.1.1 Steel................................................................................................................ 431
7.1.2 Aluminum......................................................................................................... 431
7.1.3 Concrete .......................................................................................................... 432
7.1.4 Wood............................................................................................................... 432
7.2 FUNCTIONAL STRUCTURE TYPES........................................................................... 432
7.2.1 Line Support Structures..................................................................................... 432
7.2.2 Equipment Support Structures............................................................................ 432
7.2.3 Distribution Substation Structure ........................................................................ 433
7.3 STRUCTURE MEMBER TYPES................................................................................... 433
7.3.1 Lattice ............................................................................................................. 433
7.3.2 Solid Profile ...................................................................................................... 433
7.3.3 Semi-Solid Profile ............................................................................................. 434
7.3.4 Summary.......................................................................................................... 434
7.4 DESIGN ........................................................................................................................ 434
7.4.1 Design Loads ................................................................................................... 434
7.4.2 Line Support Structures..................................................................................... 434
7.4.3 Deflection Consideration ................................................................................... 435
7.4.4 Lightning Masts................................................................................................ 436
7.4.5 Equipment Support Structures............................................................................ 436
7.4.6 Base Condition ................................................................................................. 436
7.4.7 Seismic Loads .................................................................................................. 437
7.4.8 Wind Loads...................................................................................................... 439
7.4.9 Construction Loading ........................................................................................ 440
7.4.10 Loading Combination for Design........................................................................ 441
7.4.11 Typical Design Approach.................................................................................. 441
7.5 FASTENERS ................................................................................................................. 450
7.5.1 ASTM A394 .................................................................................................... 450
7.5.2 ASTM A307 .................................................................................................... 450
7.5.3 ASTM A325 .................................................................................................... 450
7.6 WELDING..................................................................................................................... 452
7.7 FINISHES...................................................................................................................... 452
7.7.1 Galvanizing....................................................................................................... 452
7.7.2 Painting............................................................................................................ 452
7.7.3 Wood Preservatives.......................................................................................... 453
7.8 COMPUTER PROGRAMS............................................................................................ 453
7.8.1 Model Geometry............................................................................................... 453
7.8.2 Load Input........................................................................................................ 454
7.8.3 Computer Output.............................................................................................. 454
7.9 REFERENCES ................................................................................................................ 455
APPENDIX D—RISA-3D INPUT AND OUTPUT FOR A SIMPLE “T” STRUCTURE.......... 458

12. Bulletin 1724E-300
Page 12
CHAPTER 8 - FOUNDATIONS.................................................................................................... 465
8.1 GENERAL..................................................................................................................... 465
8.2 SOIL INFORMATION................................................................................................... 465
8.2.1 General............................................................................................................ 465
8.2.2 Soil Classification.............................................................................................. 466
8.2.3 Bearing Values................................................................................................. 466
8.2.4 Groundwater Level........................................................................................... 467
8.2.5 Differential Settlement ...................................................................................... 467
8.2.6 Chemical Tests................................................................................................. 468
8.2.7 Seismic Evaluation............................................................................................ 468
8.3 FOUNDATION TYPES................................................................................................. 468
8.3.1 Drilled Shafts (Piers)......................................................................................... 468
8.3.2 Drilled Shaft Design.......................................................................................... 469
8.3.3 Drilled Shaft Design (Line Support Structure)..................................................... 475
8.3.4 Compression and Uplift Capacity (Drilled Shafts)................................................ 478
8.3.5 Spread Footings ................................................................................................ 482
8.3.6 Slabs on Grade ................................................................................................. 489
8.4 OIL POLLUTION.......................................................................................................... 492
8.4.1 Basic Retention System..................................................................................... 493
8.4.2 Oil Separator Tank............................................................................................ 493
8.4.3 Summary.......................................................................................................... 494
8.5 REFERENCES ............................................................................................................... 494
APPENDIX E—SPECIFICATION FOR PROCURING GEOTECHNICAL
SUBSURFACE INVESTIGATION.......................................................................................... 497
CHAPTER 9 - GROUNDING........................................................................................................ 501
9.1 GENERAL..................................................................................................................... 501
9.2 DEFINITIONS............................................................................................................... 503
9.2.1 DC Offset........................................................................................................ 503
9.2.2 Earth Current ................................................................................................... 503
9.2.3 Ground Fault Current ........................................................................................ 503
9.2.4 Ground Potential Rise (GPR)............................................................................. 503
9.2.5 Mesh Voltage................................................................................................... 503
9.2.6 Soil Resistivity .................................................................................................. 503
9.2.7 Step Voltage..................................................................................................... 503
9.2.8 Touch Voltage.................................................................................................. 503
9.2.9 Transferred Voltage.......................................................................................... 503
9.3 SOIL RESISTIVITY MEASUREMENTS....................................................................... 504
9.3.1 Analyzing Soil Resistivity Measurements............................................................ 505
9.3.2 Uniform Soil Assumption................................................................................... 506
9.4 AREA OF THE GROUND GRID................................................................................... 506
9.5 GROUND FAULT CURRENTS..................................................................................... 506
9.5.1 Symmetrical Grid Current.................................................................................. 510
9.5.2 Determine the Split Factor, Sf............................................................................. 510
9.5.3 The Decrement Factor, Df................................................................................. 533
9.5.4 Maximum Grid Current ..................................................................................... 534
9.5.5 Asymmetrical Fault........................................................................................... 534

13. Bulletin 1724E-300
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9.6 GROUND CONDUCTOR.............................................................................................. 535
9.6.1 Conductor Material........................................................................................... 535
9.6.2 Ground Conductor Sizing................................................................................... 535
9.6.3 Sizing Equipment Ground Conductor................................................................... 536
9.6.4 Sizing Ground Grid Conductors .......................................................................... 537
9.6.5 Additional Conductor Sizing Factors................................................................... 537
9.6.6 Connections from Equipment and Structures to Ground Grid ................................ 537
9.7 SAFETY CONSIDERATIONS....................................................................................... 538
9.7.1 Tolerable Limits of Body Current....................................................................... 539
9.7.2 Typical Shock Situations.................................................................................... 540
9.8 TOLERABLE TOUCH AND STEP VOLTAGES........................................................... 540
9.9 PROTECTIVE SURFACE MATERIAL AND REDUCTION FACTOR CS .................... 545
9.9.1 Reduction Factor Cs.......................................................................................... 546
9.10 DESIGN OF A SUBSTATION GROUNDING SYSTEM................................................ 548
9.10.1 General Concepts ............................................................................................. 548
9.10.2 Design Procedures............................................................................................ 548
9.10.3 Preliminary Design............................................................................................ 550
9.10.4 Calculate Design Mesh Voltage......................................................................... 551
9.10.5 Step Voltage (Es).............................................................................................. 553
9.10.6 Ground Potential Rise (GPR)............................................................................. 554
9.10.7 Design Modifications......................................................................................... 555
9.10.8 Application of Equations for Em and Es............................................................... 557
9.10.9 Use of Computer Analysis in Grid Design........................................................... 557
9.10.10 Special Danger Points....................................................................................... 557
9.10.11 Investigation of Transferred Voltage .................................................................. 561
9.10.12 Effect of Sustained Ground Currents.................................................................. 562
9.11 REFERENCES............................................................................................................... 562
CHAPTER 10 - INSULATED CABLES AND RACEWAYS......................................................... 563
10.1 GENERAL..................................................................................................................... 563
10.2 600-VOLT CABLE ........................................................................................................ 563
10.2.1 Circuit Requirements......................................................................................... 563
10.2.2 Conductors....................................................................................................... 564
10.2.3 Conductor Configurations .................................................................................. 564
10.2.4 Conductor Insulation and Jackets....................................................................... 566
10.2.5 Cable Sizing...................................................................................................... 567
10.2.6 Segregation of Control Cables............................................................................ 567
10.2.7 Installation Considerations ................................................................................. 569
10.3 POWER CABLE OVER 600 VOLTS............................................................................. 570
10.3.1 Medium-Voltage Shielded Power Cable (2 kV up to 35 kV) ................................ 570
10.3.2 Conductors....................................................................................................... 570
10.3.3 Conductor Shield............................................................................................... 570
10.3.4 Insulation.......................................................................................................... 571
10.3.5 Insulation Shield................................................................................................ 571
10.3.6 Jackets............................................................................................................. 571
10.3.7 Cable Voltage Rating........................................................................................ 572
10.3.8 Conductor Sizing............................................................................................... 572

14. Bulletin 1724E-300
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10.3.9 Terminations and Splices................................................................................... 573
10.3.10 Cable Segregation............................................................................................. 573
10.3.11 Installation Considerations ................................................................................. 573
10.3.12 High-Voltage Power Cable (69 kV up to 230 kV)............................................... 574
10.4 SPECIALIZED CABLE................................................................................................. 574
10.5 RACEWAYS................................................................................................................. 575
10.5.1 Function........................................................................................................... 575
10.5.2 Economics........................................................................................................ 575
10.6 UNDERGROUND RACEWAYS................................................................................... 576
10.6.1 Direct-Buried Cable .......................................................................................... 576
10.6.2 Direct-Buried Conduit ....................................................................................... 577
10.6.3 Concrete-Encased Conduit (Duct Bank)............................................................. 578
10.6.4 Cable Trenches ................................................................................................ 582
10.6.5 Manholes ......................................................................................................... 584
10.6.6 Handholes........................................................................................................ 584
10.7 RACEWAY COMBINATION ....................................................................................... 585
10.8 SUMMARY—UNDERGROUND RACEWAYS............................................................ 586
10.9 OVERHEAD RACEWAYS........................................................................................... 586
10.9.1 Cable Trays...................................................................................................... 587
10.9.2 Cable Duct....................................................................................................... 587
10.9.3 Plastic Conduit.................................................................................................. 587
10.9.4 Metal Conduit................................................................................................... 587
10.9.5 Above-Grade Cable Trench............................................................................... 588
10.10 SUMMARY—OVERHEAD RACEWAYS.................................................................... 588
10.11 RACEWAY MATERIALS............................................................................................. 588
10.11.1 Plastic .............................................................................................................. 588
10.11.2 Fiber................................................................................................................ 588
10.12 RACEWAY SIZING...................................................................................................... 588
10.13 REFERENCES............................................................................................................... 589
CHAPTER 11 - CORROSION....................................................................................................... 591
11.1 GENERAL..................................................................................................................... 591
11.1.1 Characteristics of Corrosion .............................................................................. 591
11.1.2 Dissimilar Metals .............................................................................................. 591
11.1.3 Dissimilar Environments.................................................................................... 592
11.2 PRELIMINARY PREVENTIVE MEASURES ............................................................... 593
11.2.1 Surveys............................................................................................................ 593
11.2.2 Selection of Materials........................................................................................ 594
11.3 TESTING AND INSTALLATION ................................................................................. 595
11.3.1 Earth Resistivity Measurements......................................................................... 595
11.3.2 Soil Samples..................................................................................................... 595
11.3.3 Anode Locations............................................................................................... 595
11.3.4 Underground Connections ................................................................................. 595
11.3.5 Estimating Corrosion Conditions from DC Potential Measurements...................... 595
11.4 REFERENCES............................................................................................................... 598

15. Bulletin 1724E-300
Page 15
CHAPTER 12 - PROTECTIVE RELAYING.................................................................................. 601
12.1 GENERAL..................................................................................................................... 601
12.1.1 Purpose of Protective Relays............................................................................. 601
12.1.2 Design Objectives............................................................................................. 601
12.1.3 Indications of Defective Equipment or Abnormal Conditions ................................ 601
12.2 FUNDAMENTAL CONSIDERATIONS........................................................................ 603
12.2.1 Phasors............................................................................................................ 603
12.2.2 Polarity ............................................................................................................ 603
12.2.3 Faults............................................................................................................... 603
12.2.4 Symmetrical Components.................................................................................. 604
12.2.5 Relay Input Sources.......................................................................................... 604
12.3 BASIC RELAY TYPES................................................................................................. 604
12.3.1 General............................................................................................................ 604
12.3.2 Relay Selection................................................................................................. 607
12.3.3 Overcurrent Relay............................................................................................ 609
12.3.4 Distance Relay................................................................................................. 609
12.3.5 Differential Relay............................................................................................. 611
12.3.6 Overvoltage Relay............................................................................................ 612
12.3.7 Undervoltage Relay.......................................................................................... 612
12.3.8 Power Relay.................................................................................................... 612
12.3.9 Directional Overcurrent Relay........................................................................... 612
12.3.10 Frequency Relay............................................................................................... 612
12.3.11 Thermal Relay.................................................................................................. 613
12.3.12 Pressure Relay................................................................................................. 613
12.3.13 Auxiliary Relay................................................................................................. 613
12.4 RELAY SCHEMES........................................................................................................ 613
12.4.1 General............................................................................................................ 613
12.4.2 Transmission Line Protection............................................................................. 614
12.4.3 Distribution Feeder............................................................................................ 624
12.4.4 Major Equipment .............................................................................................. 626
12.4.5 Reclosing ......................................................................................................... 631
12.4.6 Coordination..................................................................................................... 633
12.5 REFERENCES.............................................................................................................. 635
APPENDIX F—STANDARD DEVICE FUNCTION NUMBERS............................................ 637
APPENDIX G—SUGGESTED SUFFIX LETTERS.................................................................. 646
CHAPTER 13 - INSTRUMENTS, TRANSDUCERS, AND METERS ............................................ 651
13.1 INTRODUCTION.......................................................................................................... 651
13.2 INSTRUMENTS AND TRANSDUCERS....................................................................... 651
13.2.1 Definitions........................................................................................................ 651
13.2.2 Types of Instruments and Transducers............................................................... 651
13.2.3 Classification of Instruments.............................................................................. 651
13.2.4 Components of Instruments and Transducers...................................................... 651
13.2.5 Analog Instrument Scales.................................................................................. 652
13.2.6 Operating Procedures ....................................................................................... 653
13.3 METERS........................................................................................................................ 654
13.3.1 Definition ......................................................................................................... 654

16. Bulletin 1724E-300
Page 16
13.3.2 Types of Electric Meters................................................................................... 654
13.3.3 Demand Meter................................................................................................. 654
13.3.4 Combination Watt-Hour and Demand Meters..................................................... 655
13.3.5 Types of Meter Indicating and Recording Devices.............................................. 655
13.3.6 Connection of Watt-Hour and VAR-Hour Meters............................................... 656
13.4 MULTI-FUNCTION METERS....................................................................................... 657
13.4.1 Definition ......................................................................................................... 657
13.4.2 Input Quantities ................................................................................................ 658
13.4.3 Measured and Calculated Values....................................................................... 658
13.4.4 Communications ............................................................................................... 658
13.5 REFERENCES............................................................................................................... 658
CHAPTER 14 - SUBSTATION AUTOMATION........................................................................... 659
14.1 INTRODUCTION.......................................................................................................... 659
14.2 OPEN VS. PROPRIETARY SYSTEMS......................................................................... 659
14.3 SUBSTATION AUTOMATION ARCHITECTURE....................................................... 660
14.4 DATA ACQUISITION AND CONTROL ELEMENTS.................................................. 660
14.4.1 Substation Host Processor................................................................................. 661
14.4.2 Intelligent Electronic Devices............................................................................. 663
14.4.3 Programmable Logic Controllers........................................................................ 664
14.4.4 Data Concentrator ............................................................................................ 665
14.4.5 Substation Local Area Network......................................................................... 665
14.4.6 Communication Protocols .................................................................................. 666
14.5 REFERENCES............................................................................................................... 669
APPENDIX H—GLOSSARY OF TERMS............................................................................... 671
CHAPTER 15 - AC AND DC AUXILIARY SYSTEMS................................................................. 673
15.1 AC AUXILIARY SYSTEM............................................................................................ 673
15.1.1 Typical Loads Supplied...................................................................................... 673
15.1.2 Design Requirements........................................................................................ 673
15.1.3 Equipment........................................................................................................ 678
15.1.4 Summary.......................................................................................................... 680
15.2 DC AUXILIARY SYSTEM............................................................................................ 680
15.2.1 Typical Loads Supplied...................................................................................... 680
15.2.2 Design Requirements........................................................................................ 681
15.2.3 Types of Cells .................................................................................................. 681
15.2.4 Typical Loads and Duty Cycle ........................................................................... 682
15.2.5 Equipment........................................................................................................ 683
15.3 REFERENCES............................................................................................................... 686
CHAPTER 16 - CONTROL HOUSES ........................................................................................... 689
16.1 INTRODUCTION.......................................................................................................... 689
16.2 CONTROL HOUSE CONSTRUCTION......................................................................... 689
16.2.1 Foundation........................................................................................................ 689
16.2.2 Floor ................................................................................................................ 689
16.2.3 Superstructure.................................................................................................. 690
16.3 CONTROL HOUSE LAYOUT ...................................................................................... 692

17. Bulletin 1724E-300
Page 17
16.3.1 Control and Relay Panels .................................................................................. 692
16.3.2 DC Equipment.................................................................................................. 695
16.3.3 AC Equipment.................................................................................................. 695
16.3.4 Cableways ....................................................................................................... 695
16.3.5 Cable Entrance................................................................................................. 696
16.3.6 Lighting............................................................................................................ 697
16.3.7 Control House HVAC Systems ......................................................................... 697
16.3.8 Control House Plumbing.................................................................................... 698
16.3.9 Communications ............................................................................................... 698
16.4 REFERENCES............................................................................................................... 698
CHAPTER 17 - COMMUNICATIONS.......................................................................................... 699
17.1 INTRODUCTION.......................................................................................................... 699
17.2 APPLICATIONS........................................................................................................... 699
17.2.1 Relaying........................................................................................................... 699
17.2.2 SCADA........................................................................................................... 699
17.2.3 Telemetering .................................................................................................... 700
17.2.4 Voice............................................................................................................... 700
17.3 METHODS.................................................................................................................... 700
17.3.1 Power Line Carrier........................................................................................... 700
17.3.2 Audio Tone ...................................................................................................... 705
17.3.3 Carrier or Audio Tone on Shield Wire ................................................................ 706
17.3.4 Microwave....................................................................................................... 706
17.3.5 Optical Fiber..................................................................................................... 709
17.3.6 Wire Lines ....................................................................................................... 711
17.3.7 Satellite Communications................................................................................... 712
17.4 REFERENCES............................................................................................................... 714
APPENDIX I—GLOSSARY OF TERMS ................................................................................ 715
CHAPTER 18 - INSPECTION....................................................................................................... 717
18.1 PURPOSE ..................................................................................................................... 717
18.2 GENERAL..................................................................................................................... 717
18.2.1 Records ........................................................................................................... 717
18.2.2 Safety.............................................................................................................. 717
18.3 PERIODIC INSPECTIONS............................................................................................ 718
18.3.1 Visual Inspections............................................................................................. 719
18.3.2 Inspection with Diagnostic Online Test Equipment .............................................. 723
18.3.3 Detailed Inspection of Major Equipment............................................................. 726
18.3.4 Internal Inspection of Transformers and Regulators ............................................ 728
18.4 NON-PERIODIC INSPECTIONS.................................................................................. 729
18.4.1 Inspection of Porcelain...................................................................................... 729
18.4.2 Fuses, Disconnects, and Other Switches............................................................. 730
18.4.3 Buses............................................................................................................... 730
18.4.4 Transformers.................................................................................................... 730
18.4.5 Transformer On-Load Tap Changers................................................................. 730
18.4.6 Regulators........................................................................................................ 730
18.4.7 Oil Circuit Reclosers......................................................................................... 730

18. Bulletin 1724E-300
Page 18
18.4.8 Circuit Breakers ............................................................................................... 730
18.4.9 Grounding System............................................................................................. 730
18.4.10 Structures......................................................................................................... 730
18.5 REFERENCES............................................................................................................... 731
CHAPTER 19 - TESTS.................................................................................................................. 733
19.1 GENERAL..................................................................................................................... 733
19.1.1 Records ........................................................................................................... 733
19.1.2 Safety.............................................................................................................. 733
19.2 DETAILED REQUIREMENTS...................................................................................... 734
19.2.1 Acceptance Tests............................................................................................. 734
19.2.2 Periodic Tests................................................................................................... 734
19.2.3 Tests After Failure............................................................................................ 734
19.3 DESCRIPTION OF TESTS............................................................................................ 734
19.3.1 Insulation Resistance Test................................................................................. 734
19.3.2 Power Factor Test............................................................................................ 737
19.3.3 DC High Potential Test..................................................................................... 737
19.3.4 Dielectric Absorption Test................................................................................. 739
19.3.5 AC Over-Potential Test .................................................................................... 740
19.3.6 Contact Resistance Test.................................................................................... 740
19.3.7 Winding Resistance Test................................................................................... 740
19.3.8 Insulating Oil Tests ........................................................................................... 741
19.3.9 Combustible Gas Analysis ................................................................................. 742
19.3.10 SF6 Gas Analyses............................................................................................. 742
19.3.11 Timing Test...................................................................................................... 742
19.3.12 Motion Analyzer Test........................................................................................ 743
19.3.13 Series Overcurrent Test.................................................................................... 743
19.3.14 Turns Ratio Test............................................................................................... 743
19.3.15 Polarity Test..................................................................................................... 743
19.3.16 Protective Relay System Tests .......................................................................... 743
19.3.17 Meter Calibration Tests..................................................................................... 744
19.3.18 Capacitance Test.............................................................................................. 744
19.3.19 Pressure Test................................................................................................... 744
19.3.20 Ground Grid Resistance Measurement ............................................................... 745
19.4 REFERENCES............................................................................................................... 745
CHAPTER 20 - MAINTENANCE................................................................................................. 747
20.1 GENERAL..................................................................................................................... 747
20.1.1 Records ........................................................................................................... 747
20.1.2 Safety.............................................................................................................. 747
20.2 PERIODIC MAINTENANCE........................................................................................ 747
20.2.1 Specific Requirements....................................................................................... 748
20.2.2 Painting............................................................................................................ 749
20.3 UNSCHEDULED MAINTENANCE.............................................................................. 750
20.4 RELIABILITY-CENTERED MAINTENANCE.............................................................. 751
20.4.1 Methods........................................................................................................... 751
20.4.2 Application....................................................................................................... 752

19. Bulletin 1724E-300
Page 19
20.4.3 Conclusion........................................................................................................ 754
20.5 REFERENCES............................................................................................................... 754
CHAPTER 21 - UPRATING AND EXPANDING EXISTING SUBSTATIONS.............................. 755
21.1 APPLICABILITY.......................................................................................................... 755
21.2 FEASIBILITY................................................................................................................ 755
21.3 SUBSTATION UPRATING........................................................................................... 755
21.3.1 Major Equipment Uprating................................................................................. 756
21.4 SUBSTATION EXPANSION......................................................................................... 758
21.4.1 General............................................................................................................ 758
21.4.2 Site Work......................................................................................................... 760
21.4.3 Grounding......................................................................................................... 760
21.4.4 Raceway System.............................................................................................. 760
21.4.5 Control House .................................................................................................. 761
21.4.6 Equipment........................................................................................................ 761
21.5 PLANNING FOR UPRATING OR EXPANSION.......................................................... 762
21.6 COMPARISONS—NEW VS. UPRATING OR EXPANSION........................................ 763
21.7 SUBSTATION UPGRADING........................................................................................ 763
21.8 REFERENCES............................................................................................................... 764

20. Bulletin 1724E-300
Page 20
LIST OF FIGURES
These exhibits are available electronically as well as in hard copy.
FIGURE TITLE
2-1 Basic Wind Speed.....................................................................................................48
2-2 Seismic Zone Map of the United States......................................................................50
3-1 Power Transformer ..................................................................................................60
3-2 Three-Phase Transformer with Tertiary.....................................................................60
3-3 Three-Phase Auto-Transformer.................................................................................60
3-4 Step Voltage Regulator with Bypass Switch...............................................................61
3-5 Hook Stick-Operated Disconnecting Switch................................................................61
3-6 Three-Phase Gang-Operated Disconnecting Switch with Horn Gaps and
Grounding Switch......................................................................................................61
3-7 Three-Phase Double Side-Break Disconnecting Switch with Motor Operator ...............62
3-8 Fused Disconnect.....................................................................................................62
3-9 Oil Circuit Recloser...................................................................................................63
3-10 Circuit Breaker.........................................................................................................63
3-11 Surge Arrester..........................................................................................................63
3-12 Voltage Transformer.................................................................................................64
3-13 Current Transformer.................................................................................................64
3-14 Coupling Capacitor with Voltage Transformer ............................................................64
3-15 Coupling Capacitor, Wave Trap, Tuning Unit, and Power Line Carrier
Transmitter/Receiver ................................................................................................64
3-16 Disconnecting Clamp ................................................................................................65
3-17 Shunt Capacitor ........................................................................................................65
3-18 One-Line Diagram Symbols.......................................................................................66
3-19 Typical Relay and Meter Representation....................................................................67
3-20 Conceptual One-Line Diagram..................................................................................68
3-21 Partial Switching One-Line Diagram..........................................................................69
3-22 Partial Functional Relaying One-Line Diagram............................................................70
4-1 Substation Plan View Showing Space for Equipment Removal................................... 121
4-2 Basic Distribution Substation.................................................................................... 122
4-3 Voltage Regulator Bypass Arrangements................................................................. 123
4-4 Typical Circuit Breaker/Recloser Bypass Arrangement............................................. 124
4-5 Use of Tandem Switches for Circuit Breaker/Recloser Bypassing ............................. 124
4-6 Basic Transmission Substation................................................................................. 125
4-7 Typical Circuit Breaker Bypass Arrangement........................................................... 126
4-8 Basic Switching Substation...................................................................................... 128
4-9 Single Bus—Low Profile ......................................................................................... 130
4-10 Single Bus—High Profile......................................................................................... 131
4-11 Sectionalized Bus.................................................................................................... 132
4-12 Main and Transfer Bus—Low Profile ...................................................................... 134
4-13 Main and Transfer Bus—High Profile ...................................................................... 135
4-14 Ring Bus ................................................................................................................ 137
4-15 Breaker-and-a-Half ................................................................................................ 138

21. Bulletin 1724E-300
Page 21
FIGURE TITLE
4-16 Double Breaker–Double Bus................................................................................... 140
4-17 Zones of Protection for Masts and Shield Wires Using Fixed Angle Method............... 143
4-18 Principle of Rolling Sphere....................................................................................... 144
4-19 Station Post Insulator .............................................................................................. 148
4-20 Suspension Insulator................................................................................................ 152
4-21 Safety Clearance to Electric Supply Station Fences................................................... 158
4-22 Drag Coefficients for Structural Shapes ................................................................... 166
4-23 Typical Bus System Illustrating Provisions for Conductor Thermal Expansion ............. 169
4-24 Coupler Location .................................................................................................... 175
4-25 Bus Configuration for Example ................................................................................ 176
4-26 Short Strain Bus Insulator Effect.............................................................................. 180
5-1 Methods of Oil Preservation.................................................................................... 211
5-2 “Dead Tank” Breaker............................................................................................. 222
5-3 “Live Tank” Breaker.............................................................................................. 222
5-4 Three-Pole Single-Throw Breakers.......................................................................... 223
5-5 SF6 Gas Circuit Breakers ........................................................................................ 224
5-6 Type SDV Vacuum Circuit Breaker ........................................................................ 225
5-7 Relation of Symmetrical Interrupting Capability, Closing Capability, Latching
Capability, and Carrying Capability to Rated Short-Circuit Current ............................. 235
5-8 Ratio of Circuit Breaker Asymmetrical to Symmetrical Interrupting Capabilities.......... 236
5-9 Single-Aisle Metal-Clad Switchgear with Ancillaries ................................................. 247
5-10 Typical Single-Aisle Switchgear Installation.............................................................. 248
5-11 Single-Phase Voltage Regulator............................................................................... 255
5-12 Three-Phase Voltage Regulator............................................................................... 256
5-13 Typical Capacitor Bank—Two Three-Phase Capacitor Racks Connected to
Form a Two-Step Bank, Floating Wye with a Common Neutral................................. 264
5-14 A Y-Y Connected Capacitor Bank with One Series Section per Phase and
Neutrals Isolated..................................................................................................... 270
5-15 Typical Capacitor Bank Grd Wye Connected............................................................ 273
5-16 Typical Capacitor Bank Floating Wye ...................................................................... 274
5-17 Typical Capacitor Bank Wye Wye Connected.......................................................... 275
5-18 A Complete Typical Capacitor Equipment Connected Grd Wye with Two
Series Sections/Phase in a Single Stack.................................................................... 276
5-19 Typical Internally and Externally Fused Capacitor Units ............................................ 281
5-20 Capacitors Vertically Mounted................................................................................. 286
5-21 Capacitors Horizontally Mounted............................................................................. 287
5-22 Horizontally Mounted Double-Break Switch with Grounding Switch........................... 300
5-23 Horizontally Mounted Double-Break Switch............................................................. 300
5-24 Horizontally Mounted Vertical-Break Interrupter Switch........................................... 301
5-25 Vertically Mounted Vertical-Break Switch............................................................... 304
5-26 Tilting Insulator Switch............................................................................................ 305
5-27 Single Side-Break Switch........................................................................................ 306
5-28 Underhung Center-Break V-Switch......................................................................... 306
5-29 Hook Stick Switches on Structure at Termination of Bus from Transformer................ 307
5-30 Vertical Reach Switch............................................................................................ 307

22. Bulletin 1724E-300
Page 22
FIGURE TITLE
5-31 Arrangement of Bolt Hole Centerlines in Terminal Pads............................................ 315
5-32 Outdoor Air Switch Hook Dimensions...................................................................... 322
5-33 Coefficient of Grounding for Various System Conditions............................................ 336
5-34 Typical Voltage–Time Curve for Coordination of Arrester Protective Levels
with Insulation Withstand Strength for Liquid-Filled Transformers.............................. 338
5-35 Typical Volt–Time Curves for Coordination of Metal Oxide Surge Arrester
Protective Levels with Insulation Withstand Strength................................................. 341
5-36 Gapless Metal Oxide Surge Arrester........................................................................ 342
5-37 Shunt-Gapped Metal Oxide Surge Arrester............................................................... 343
5-38 Series-Gapped Metal Oxide Surge Arrester.............................................................. 343
5-39 Typical 60-Hz Temporary Overvoltage Capability for Metal Oxide Arresters.............. 345
5-40 Typical Volt–Time Curve for Coordination of Arrester Protective Levels with
Insulation Withstand Strength for Liquid-Filled Transformers ..................................... 348
5-41 Typical Volt–Time Curves for Coordination of 152-kV MCOV Metal Oxide
Surge Arrester Protective Levels with Insulation Withstand Strength.......................... 350
5-42 Typical Volt–Time Curves for Coordination of 140-kV MCOV Metal Oxide
Surge Arrester Protective Levels with Insulation Withstand Strength.......................... 351
5-43 Maximum Safe Separation Distance of Lightning Arresters from Protected
Equipment—Nominal System Voltage 23 kV Through 46 kV..................................... 353
5-44 Maximum Safe Separation Distance of Lightning Arresters from Protected
Equipment—Nominal System Voltage 69 kV Through 138 kV................................... 354
5-45 Maximum Safe Separation Distance of Lightning Arresters from Protected
Equipment—Nominal System Voltage 161 kV Through 345 kV ................................. 355
5-46 Typical Single-Phase Hydraulically Controlled Oil Circuit Breaker.............................. 358
5-47 Recloser with Single-Phase Tripping and Three-Phase Lockout................................. 359
5-48 Typical Line Diagram of Distribution Circuit Showing Application of Reclosers........... 360
5-49 Operating Mechanism with Housing Cover Removed................................................ 372
5-50 Unit Operation........................................................................................................ 373
5-51 Recloser Operating Sequence Upon Occurrence of a Permanent Fault ...................... 374
5-52 Mounted Recloser................................................................................................... 376
5-53 55ºC Rise Current Transformer Basic Loading Characteristics (in Air) ...................... 380
5-54 Bushing, Window, and Wound-Type Current Transformers ....................................... 383
5-55 High-Voltage Current Transformers......................................................................... 384
5-56 Voltage Transformers............................................................................................. 390
5-57 Typical Primary Connections for Voltage Transformers ............................................ 397
5-58 Coupling Capacitor with Carrier Accessories............................................................ 400
5-59 Typical Coupling Capacitor Voltage Transformer with Carrier Coupling
Accessories............................................................................................................ 402
5-60 Coupling Capacitor Voltage Transformers with and Without Wave Trap.................... 405
6-1 Flat Yard................................................................................................................ 413
6-2 Sloped Yard on Moderately Sloped Site.................................................................... 413
6-3 Stepped Yard......................................................................................................... 414
6-4 2-Year, 30-Minute Rainfall Intensity (cm/hr)............................................................. 417
6-5 2-Year, 30-Minute Rainfall Intensity (inches/hr)........................................................ 417
6-6 Fence Erection Details ............................................................................................ 430

23. Bulletin 1724E-300
Page 23
FIGURE TITLE
7-1 Single-Phase Bus Support........................................................................................ 442
7-2 Tubular Structure—Short-Circuit Loading................................................................. 443
7-3 Tubular Structure—Wind Loading............................................................................ 443
7-4 Tubular Structure—Ice Loading............................................................................... 444
7-5 Tubular Structure—Seismic Loading........................................................................ 445
7-6 Tubular Structure—Deflection Equivalent Loadings .................................................. 446
7-7 Lattice Structure..................................................................................................... 448
7-8 Lattice Structure—Short-Circuit Loading.................................................................. 448
7-9 Lattice Structure—Wind Loading............................................................................. 449
8-1 Drilled Shaft Force and Moment Diagrams............................................................... 473
8-2 Drilled Shaft Elevation—Example ............................................................................ 473
8-3 Drilled Shaft Section ............................................................................................... 476
8-4 Drilled Shaft Elevation—General............................................................................. 477
8-5 “Alpha” Function for Drilled Shafts.......................................................................... 480
8-6 Approximate Frost-Depth Contours of the United States ........................................... 483
8-7 Spread Footing—General........................................................................................ 484
8-8 Spread Footing with e < b/6..................................................................................... 485
8-9 Spread Footing with e > b/6..................................................................................... 485
8-10 Spread Footing Elevation......................................................................................... 486
8-11 Spread Footing Plan................................................................................................ 487
8-12 Spread Footing—3D Example.................................................................................. 487
8-13 Spread Footing—2D Example.................................................................................. 488
8-14 Transformer Slab Loading....................................................................................... 492
8-15 Oil Separator Tank.................................................................................................. 494
9-1 Wenner Four-Pin Method........................................................................................ 505
9-2 Fault Within Local Substation, Local Neutral Grounded............................................. 507
9-3 Fault Within Local Substation, Neutral Grounded at Remote Location......................... 507
9-4 Fault in Substation, System Grounded at Local Substation and Also at Other Points..... 508
9-5 Typical Current Division for a Fault on High Side of Distribution Substation................ 509
9-6 Approximate Split Factor Sf, 100% Remote, 1 Transmission Line, Low Line
Ground Resistance.................................................................................................. 511
9-7 Approximate Split Factor Sf, 100% Remote, 1 Transmission Line, High Line
Ground Resistance.................................................................................................. 512
9-8 Approximate Split Factor Sf, 100% Remote, 2 Transmission Lines, Low Line
Ground Resistance.................................................................................................. 513
9-9 Approximate Split Factor Sf, 100% Remote, 2 Transmission Lines, High Line
Ground Resistance.................................................................................................. 514
9-10 Approximate Split Factor Sf, 100% Remote, 4 Transmission Lines, Low Line
Ground Resistance.................................................................................................. 515
9-11 Approximate Split Factor Sf, 100% Remote, 4 Transmission Lines, High Line
Ground Resistance.................................................................................................. 516
9-12 Approximate Split Factor Sf, 100% Remote, 8 Transmission Lines, Low Line
Ground Resistance.................................................................................................. 517
9-13 Approximate Split Factor Sf, 100% Remote, 8 Transmission Lines, High Line
Ground Resistance.................................................................................................. 518