This document discusses strategies for mitigating arc flash hazards in metalclad switchgear. It covers arc flash standards, prevention techniques, protection methods, and mitigation approaches. Key topics include implementing fast bus tripping, high speed differential relays, maintenance relay settings, arc flash detection, current limiting fuses, and reducing the human interface with remote racking and control. The goal is to reduce incident energy levels and protect personnel through engineering and procedural controls.

1. ARC FLASH MITIGATION
STRATEGIES
for
METALCLAD
SWITCHGEAR
PEDERSEN POWER PRODUCTS
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2. Discussion Topics
 Arc Flash Standards
 Arc Flash Prevention
 Arc Flash Protection
 Mitigation Techniques

3. Arc Flash Hazards
Molten Metal
Intense Heat
Droplets
35,000F
Flying Objects
& Shrapnel
Toxic Gases
Copper Solid to Intense
Vapor Expansion Light Flash
67,000 Times
Sound
Blast
Pressure
Wave

4. ARC FLASH
STANDARDS
PEDERSEN POWER PRODUCTS
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5. IEEE Standard 1584
Contains calculations used to determine
safe boundary distances for unprotected
personnel and the incident energy at the
working distance for qualified personnel
working on energized equipment.

6. IEEE Standard 1584
Incident Energy Calculation for
Arc Flash in a Cubic Box
E =1038.7D-1.4738 x T[0.0093F2-0.3453F+5.9675]
E = Incident Energy in cal/cm2
D = Distance to arcing point
T = Time to clear arcing fault
F = Available bolted fault short circuit current

7. NFPA-70E-2009
Standard for Electrical Safety
in the Workplace
Utilizes IEEE 1584 methods for
calculating incident energy on
specific electrical equipment and
provides guidelines for the PPE
clothing required based on the
incident energy level.

8. National Electric Code
Requires labeling of electrical equipment
to warn qualified personnel of the danger
of electric arc flash.
Refers to NFPA-70E as a guide for
quantifying the hazard.

9. Arc Flash Warning Label
Compliance with National Electric Code

10. Arc Flash Warning Label

11. OSHA 29 CFR Part 1910
1910.333 Selection and Use of Work Practices
Safety-related work practices to prevent injuries resulting
from either direct or indirect electrical contact, when
work is performed near or on equipment or circuits which
may be energized.
1910.335 Safeguards for Personal Protection
PPE shall be used to protect employees from
electrically related injuries while that employee is
working near exposed energized parts.
Subpart S, Appendix A
References NFPA-70E for
Electrical Safety Practices

12. ARC FLASH
PREVENTION
PEDERSEN POWER PRODUCTS
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13. Arc Flash Prevention
DON’T
WORK ON
ENERGIZED
ELECTRICAL
EQUIPMENT!

14. Causes of Electric Arc Flash
 Contact with Live Parts
 Unsafe Work Procedures
 Misoperation
 Insufficient Maintenance
 Overvoltages
 Insulation Failure
 Entry of Small Animals

15. Arc Flash Prevention
 Maintain Sound Safety Practices
 Prevent Entry of Critters
 Use IEEE Metalclad Standards
 Prevent Moisture Ingress
 Proper Insulation System Design
 Monitor for Partial Discharge
 Monitor Bus Temperatures

16. IEEE Standard C37.20.7
“There is little likelihood of an internal arc in
equipment meeting the requirements of IEEE Standard
C37.20.1-2002 or IEEE Standard C37.20.3-2001. There
is even less likelihood of an internal arc in equipment
that has insulated bus, compartmentalization, barriers,
and interlocks, such as those described in IEEE
Standard C37.20.2-1999.”
Metalclad Switchgear Design Standard

17. Metal Enclosed Switchgear
Line
Terminals Uninsulated Bus
Load break
air switch
Everything in Same
Compartment
Exposed
Live Parts
with Fuse
Door Open
Load
Terminals
Ground bus

18. Metalclad Switchgear
Relay, Controls Primary buses and
and connections covered
Instrumentation with insulation
Shutters cover Main bus
Primaries when
Primary circuits,
no breaker installed
relays, meters,
and controls
isolated in own CT barrier CT
grounded metal Load
compartments bus
Movable
Shutters CT
Breaker
Compartment
Ground bus

19. Metalclad Switchgear
Relay, Controls
and
Instrumentation
Main bus
Steel barrier
CT
No primary circuits Load
exposed with bus
breaker installed Vacuum
CT
Breaker
Ground bus

20. Arc Flash Prevention
 Maintain Good Safety Practices
 Prevent Vermin Entry
 Use IEEE Metalclad Standards
 Prevent Moisture Ingress
 Proper Insulation System Design
 Monitor for Partial Discharge
 Monitor Bus Temperatures

21. Moisture Prevention
 IEEE Tested Enclosure Design
 Use Extended Life Sealants
IEEE C37.20.2 Section 6.2.10
 Ventilate Test Criteria
Cable Compartment
7.1 gallonsFilters/Screens rate
• Maintain per minute flow
60psi Dualwater pressure
• Use min Strip Heaters
10 ft. Min Distance from Joints
• Monitor Strip Heaters
Against 2 Surfaces at each Joint
• Seal Unintentional Openings
 Apply Quality Protective Finish

22. Arc Flash Prevention
 Maintain Good Safety Practices
 Prevent Vermin Entry
 Use IEEE Metalclad Standards
 Prevent Moisture Ingress
 Proper Insulation System Design
 Monitor for Partial Discharge
 Monitor Bus Temperatures

23. Insulation Materials
95kV BIL Rated Insulators
Fluidized Bed Epoxy Bus Insulation
Cycloaliphatic
bus supports
PVC
Insert

24. Arc Flash Prevention
 Maintain Good Safety Practices
 Prevent Vermin Entry
 Use IEEE Metalclad Standards
 Prevent Moisture Ingress
 Proper Insulation System Design
 Monitor for Partial Discharge
 Monitor Bus Temperatures

25. Partial Discharge Monitoring
Signal
sent to
InsulGard
RFCT #1 detects partial Relay
discharges internal to
switchgear compartment.
RFCT #2 detects partial
discharges in Customer’s
cables up to 100 ft from
switchgear

26. Partial Discharge Monitoring

27. Arc Flash Prevention
 Maintain Good Safety Practices
 Prevent Vermin Entry
 Use IEEE Metalclad Standards
 Prevent Moisture Ingress
 Proper Insulation System Design
 Monitor for Partial Discharge
 Monitor Bus Temperatures

28. Temperature Monitoring
Bus
Joint Wireless Parasitically Powered
Temperature Detectors for
Medium Voltage Switchgear
Straight
(under development)
Bus

29. Output Through Internet
Protection system configuration
Temperature input from sensors
Current Input from CT’s
Calculate and Predict a Problem
Email/Alarm notification

30. ARC FLASH
PROTECTION
PEDERSEN POWER PRODUCTS
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31. Arc Flash Protection
 Train Personnel
 Wear Proper PPE
 Install Warning Labels
 Maintain Good Safety Practices
 Build Sturdy Enclosure
 Reduce the Human Interface
 Redirect the Blast Energy

32. Safety Practices
 De-Energize Equipment
 Use Lockout/Tagout Procedures
 Latch and Secure All Panels
 Label Line and Load Side Bus
 Isolate Potential Backfeeds
 Open Tie Breaker/Redundant Sources
 Ground De-Energized Conductors

33. Safety Practices
IEEE C37.20.6-2007 G&T TESTING STANDARD
 First G&T Standard
 Established Formal G&T Tests
 BIL Withstand
 AC Hipot 1-minute
 Momentary For 10 Cycles Per
C37.20.2
 K*I 2 Seconds Per C37.20.2
 Interlocking (Upper & Lower)
 500 Insertions and Removals

34. Safety Practices
Ball Type Ground & Test Device

35. Safety Practices
Ground Conductor Sizing
25kA for 2 seconds
Requires three (3) – 350mcm
cables per phase
(total of 9 grounding cables)
Ground Conductor Sizing
31.5kA for 2 seconds
Requires three (3) – 500mcm
cables per phase
(total of 9 grounding cables)

36. Safety Practices

37. Arc Flash Protection
 Train Personnel
 Wear Proper PPE
 Install Warning Labels
 Maintain Good Safety Practices
 Build Sturdy Enclosure
 Reduce the Human Interface
 Redirect the Blast Energy

38. Sturdy Enclosure Design
 Use Only 11 Gauge Steel
 Weld Cubicles
 Two Walls Between Sections
 Heavy Duty Door Hinges
 Heavy Duty Door Latches

39. Arc Flash Protection
 Train Personnel
 Wear Proper PPE
 Install Warning Labels
 Maintain Good Safety Practices
 Build Sturdy Enclosure
 Reduce Human Interface
 Redirect the Blast Energy

40. Reduce Human Interface
Opening & Closing Breaker
 Relocate control switch
 Use remote communications
 Use local HMI
 Use remote control station
 Use Remote Operator
 Use Time Delay Control Switch

41. Reduce Human Interface
Remote Breaker Control
Smart
Remote
Control
Station

42. Reduce Human Interface
Remote Breaker Control
ELECTROSWITCH

43. Reduce Human Interface
Remote Breaker Racking
Remote Breaker
Racking Motor
Remote
Breaker
Racking
Motor

44. Reduce Human Interface
Remote Breaker Racking

45. Reduce Human Interface
Remote Breaker Racking

46. Arc Flash Protection
 Train Personnel
 Wear Proper PPE
 Install Warning Labels
 Maintain Good Safety Practices
 Build Sturdy Enclosure
 Reduce the Human Interface
 Redirect the Blast Energy

47. IEEE Standard C37.20.7

48. IEEE Standard C37.20.7
A procedure for testing and evaluating
the performance of medium-voltage
metal-enclosed switchgear for internal
arcing faults and identifying the
capabilities of the equipment relative
to specific zones of protection.
NOT A DESIGN STANDARD

49. IEEE Standard C37.20.7
Arc-Resistant Definition:
“Equipment designed to withstand
the effects of an internal arcing
fault as indicated by successfully
meeting the requirements of IEEE
Standard C37.20.7-2007.”

50. IEEE Standard C37.20.7
Term Arc Resistant can be misleading.
In the event of an internal arcing fault,
the dangerous effects of the arc are
vented away from the zone of
protection for personnel.
Term Arc Venting is more accurate

51. Arc Venting Switchgear

52. Arc Venting Switchgear
48” min
95”
Duct can exit to the
left, right, or rear

53. Arc Venting Switchgear
Exhaust Vent Duct Design
 Tested on the switchgear
 Must vent to safe area
 Fire rated at wall opening
 No external air allowed in
 Prevent buildup of ice and snow
 Prevent critter ingress

54. IEEE Standard C37.20.7
“Not intended to provide this additional degree of
“Intended to provide an additional degree of
protection to operating personnel who, in thenormal
protection to the personnel performing normal
performance of their duties, would be required to
operating duties in close proximity to the equipment
open enclosure doors or panels or otherwise alter the
while equipment is operating under normal
equipment from its normal operating conditions.”
conditions”

55. IEEE Standard C37.20.7
IEEE does not require that metalclad
switchgear to be manufactured to
pass the IEEE Standard C37.20.7
Testing Procedures.

56. IEEE Standard C37.20.7
Zones
of
Protection

57. Zones of Protection
Type 1
Switchgear with arc-
resistant designs or
features at the freely
accessible front of the
equipment only.

58. Zones of Protection
Type 2
Switchgear with arc-
resistant designs or
features at the freely
accessible exterior
(front, back and sides)
of the equipment only.

59. Zones of Protection
Type 1B
That arcing does not
cause holes in the freely
accessible front of the
enclosure or in the walls
isolating the low-voltage
control or instrument
compartments.

60. Zones of Protection
Type 2B
That arcing does not
cause holes in the freely
accessible front, sides
and rear of the enclosure
or in the walls isolating
the low-voltage control or
instrument
compartments.

61. Zones of Protection
Type 1BC
Adds isolation from
effects of an internal
arcing fault between all
adjacent compartments

62. Zones of Protection
Type 2BC
Adds isolation from
effects of an internal
arcing fault between all
adjacent compartments

63. Arc Venting Switchgear
Considerations
 Initial cost (up to 25% more)
 Need breaker lift device
 Must design room accordingly
 Must seal all cable entries
 Low voltage wiring protection
 Loss of protection if door/panel open

64. IEEE Standard C37.20.7
Testing Does Not Address…
 Protection against toxic gases
 Protection against excessive sound
 Arcing within components
 Protection from above or below

65. ARC FLASH
MITIGATION
PEDERSEN POWER PRODUCTS
Th Sign o Quality
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66. Arc Flash Mitigation
Incident Energy Calculation
E =1038.7D-1.4738 x T[0.0093F2-0.3453F+5.9675]
E = Incident Energy in cal/cm2
D = Distance to arcing point
T = Time to clear arcing fault
F = Available short circuit current

67. Arc Flash Mitigation
 Complete System Analysis
 High Speed Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

68. Fast Bus Tripping
50/62
50
50
50
50
50
T

69. Fast Bus Tripping
50/62
T
50
50
50
50
50

70. Arc Flash Mitigation
 Complete System Analysis
 High Speed Bus Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

71. Maintenance Relay Settings
Relay Group Settings Feature can be enabled
by a contact input, communications or ARMs
Selector Switch to enable “Maintenance Mode”
protective settings when maintenance is being
performed on the equipment.
“Maintenance Mode” Protective Group settings
typically establish lower instantaneous pick-
ups that can be optimized to reduce trip delays
and increase sensitivity, but avoid nuisance
trips.
Remote and/or Local Visual Indication can be
provided to confirm the Relay is in Maintenance
Mode.
ARMs
Selector
Switch
TB2
FP5000
Relay Maintenance Mode
a b Indicating Light ARM’s Selector Switch
FP5000 Postion A Position B
Relay Settings Group 2 Group 1
Group Maintenance Mode Normal Mode
CI - 7
Relay Contact
CI - 8 CI-7 CI-8
Input

72. Arc Flash Mitigation
 Complete System Analysis
 High Speed Bus Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

73. Arc Flash Detection
Microprocessor based high speed relay
sends trip signal to breaker upon sensing
a light flash with high speed light sensors
installed in the
switchgear
compartments.

74. Arc Flash Detection
SEL-751A Feeder Protection Relay
Instantaneous Overcurrent
Timed Overcurrent
Instantaneous Neutral Overcurrent
Times Neutral Overcurrent
Undervoltage (Bus Side)
Overvoltage (Bus Side)
Undervoltage (Line Side)
Overvoltage (Line Side)
Over Frequency
Under Frequency
Syncronism Check
Auto-Reclosing
Arc-Flash Detection
Arc-Flash Overcurrent

75. Arc Flash Detection
Test Cell Without Arc Flash Detection

76. Arc Flash Detection
Test Cell With Arc Flash Detection

77. Arc Flash Detection
Switchgear Without Arc Flash Detection

78. Arc Flash Detection
Switchgear With Arc Flash Detection

79. Arc Flash Detection
Test Dummy Without Arc Flash Detection

80. Arc Flash Detection
Test Dummy With Arc Flash Detection

81. Arc Flash Mitigation
 Complete System Analysis
 High Speed Bus Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

82. Arc Terminator
Detects presence of an arc flash with high
speed photo sensors and closes a high
speed switch that shorts out the the main
bus in the first ¼ cycle to create a parallel
path to the arc and quickly extinguish a
burning arc

83. Arc Terminator

84. Arc Terminator

85. Arc Terminator
Phase B Phase C
Phase A

86. Arc Terminator
Arc

87. Arc Terminator
 Confines Arc Effects at Initiation Point
 Extinguishes Arc < ¼ Cycle
 Prevents Pressure Buildup
 No Change to Relay Coordination
 Integrated Into Switchgear Lineup
 Indicates Where Flash was Detected.
 Limited to 40ka Symmetrical Faults

88. Arc Flash Mitigation
 Complete System Analysis
 High Speed Bus Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

89. Arc Flash Mitigation
 Complete System Analysis
 High Speed Bus Differential Relay
 Fast Bus Tripping
 Maintenance Relay Settings
 Arc Flash Detection
 Hi-Speed Arc Terminator
 3 Cycle Breakers
 Current Limiting Fuses

90. Current Limiting Fuses
Current Limiting Protector (CLiP)
Up to 5,000A Continuous @15.5kv
Up to 120,000A Interrupting

91. Current Limiting Fuses
10ka Trigger Element
limits peak to 17ka vs
48ka

92. Scheme Comparison
5 Cycle Breakers 3 Cycle Breakers
Arcing Percent Arcing Percent
Protection Scheme Time Reduction Time Reduction
Normal Coordination 800ms 0% 767ms 0%
Fast Bus Trip 170ms <79%> 137ms <83%>
Maintenance Settings 120ms <85%> 87ms <89%>
High Speed Differential 107ms <87%> 74ms <91%>
Arc Flash Detection 86ms <89%> 53ms <93%>
Arc Terminator 2.3ms <99.7%> 2.3ms <99.7%>

93. NFPA
Personal
Protective
Equipment
Requirements
PEDERSEN POWER PRODUCTS
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94. NFPA PPE Requirements
Incident Required
Energy PPE Minimum
Present Risk PPE Rating Protective Clothing Required to Prevent
(cal/cm2) Cat (cal/cm2) Onset of a Second Degree Burn
E ≤ 1.2 0 N/A Untreated Cotton
1.2 < E ≤ 4 1 4 FR Shirt + FR Pants
4<E≤8 2 8 Cotton Undergarments + FR Shirt + FR Pants
8 < E ≤ 25 3 25 Cotton Undergarments + FR Shirt + FR Pants
+ FR Coverall
25 < E ≤ 40 4 40 Cotton Underwear + FR Shirt + Pants
+ Multi-Layer Flash Suit (minimum of 3 layers)
E > 40 N/A N/A Too Dangerous to Work On

95. NFPA PPE Requirements
NO CALCULATION OF INCIDENT ENERGY
NFPA Table 130.7(C)(9) – 1Kv – 38Kv Switchgear
Tasks Performed on Energized Equipment Risk Cat
Inspections Outside Restricted Approach Boundary 3
Operate Circuit Breaker with Door Closed 2
Operate Circuit Breaker with Door Open 4
Operate Meter Switch 0
Work on Energized Electrical Conductors 4
Work on Exposed Control Energized Circuits <120V 2
Work on Exposed Control Energized Circuits >120V 4
Racking of Breakers with Door Open or Closed 4
Application of Safety Grounds After Voltage Test 4
Remove Covers to Expose Energized Conductors 4
Open Hinged Covers to Expose Energized Conductors 3
Open PT or SST Compartment 4

96. NFPA PPE Requirements
NO CALCULATION OF INCIDENT ENERGY
NFPA Table 130.7(C)(9) – 1Kv – 38Kv Switchgear
IF ARC RESISTANT SWITCHGEAR UTILIZED
(for clearing times less than 500ms)
Non AR AR Swgr
Tasks Performed on Energized Equipment Risk Cat Risk Cat
Operate Circuit Breaker with Door Closed 2 0
Operate Circuit Breaker with Door Open 4 4
Work on Energized Control Circuits <120V 2 0
Work on Energized Control Circuits >120V 4 4
Racking of Breakers with Door Open 4 4
Racking of Breakers with Door Closed 4 0
Insert or Withdraw Potential Transformers 4 0

97. E (cal/cm2) versus Fault Current
5 Cycle Breaker
Protection Scheme 25ka 40ka 50ka 63ka
Normal Coordination 13.30 29.70 50.50 89.30
Fast Bus Trip 2.83 6.32 10.73 18.97 PPE
E
Maintenance Settings 2.00 4.46 7.58 13.39 (cal/cm2) Cat
High Speed Differential 1.78 3.98 6.76 11.94 1.2 0
Arc Flash Detection 1.47 3.20 5.43 9.60 4 1
3 Cycle Breaker 8 2
Protection Scheme 25ka 40ka 50ka 63ka 25 3
Normal Coordination 12.75 28.5 48.40 85.60 40 4
Fast Bus Trip 2.28 5.09 8.65 15.29
>40 N/A
Maintenance Settings 1.45 3.23 5.49 9.71
High Speed Differential 1.23 2.75 4.67 8.26
Arc Flash Detection 0.88 1.97 3.35 5.91

98. E (cal/cm2) versus Distance
Normal Coordination (5 cycle)
100
90
PPE
E
80 FC = 25ka (cal/cm2) Cat
FC = 40ka
1.2 0
Incident Energy (cal/cm2)
70
FC = 50ka
60 FC = 63ka 4 1
50 PPE 8 2
Cat
40 25 3
4
30 40 4
20 >40 N/A
3
10
2
0 1
0 6 12 18 24 30 36
Distance to Arcing Point (inches)

99. E (cal/cm2) versus Distance
PPE
Normal Coordination (5 cycle) Cat
40
PPE
35
FC = 25ka
E
FC = 40ka 4 (cal/cm2) Cat
FC = 50ka
30
1.2 0
Incident Energy (cal/cm2)
FC = 63ka
25
4 1
20
3 8 2
15
25 3
10
2 40 4
5
1 >40 N/A
0
0 12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216
Distance to Arcing Point (inches)
(216” = 18’)

100. E (cal/cm2) versus Distance
PPE
Bus Differential + Arc Flash (3 cycle) Cat
40
FC = 25ka
35
FC = 40ka 4 PPE
E
30
FC = 50ka
(cal/cm2) Cat
Incident Energy (cal/cm2)
FC = 63ka
1.2 0
25
4 1
20 8 2
3 25 3
15
40 4
10
>40 N/A
2
5
1
0 0
0 6 12 18 24 30 36
Distance to Arcing Point (inches)

101. Remote Racking/Control Advantages
Normal Coordination (800ms clearing time)
Standard 5 cycle Breakers
Fault Operation at Front Operation at 20 Feet E PPE
Current of Cubicle Door from Cubicle Door
(cal/cm Cat
2)
2
25kA 8.31 cal/cm 0.51 cal/cm2 1.2 0
40kA 18.58 cal/cm2 1.13 cal/cm2
4 1
50kA 31.56 cal/cm2 1.93 cal/cm2
63kA 55.79 cal/cm2 3.40 cal/cm2 8 2
25 3
Bus Differential Protection (107ms interrupt) 40 4
Standard 5 cycle Breakers >40 N/A
Fault Operation at Front Operation at 20 Feet
Current of Cubicle Door from Cubicle Door
2
25kA 1.78 cal/cm 0.11 cal/cm2
40kA 3.98 cal/cm2 0.24 cal/cm2
50kA 6.76 cal/cm2 0.41 cal/cm2
63kA 11.94 cal/cm2 0.73 cal/cm2

102. Recommended Scheme
Transformer Differential Protection
Bus Differential Protection
Arc Flash Detection
To CT’s at
Transformer
87T Zone
87B Zone
Arc Flash
Detection
Zones

103. PPP
Think
PEDERSEN