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ETAP - Coordination and protecion 2
1.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection and Coordination
2.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Agenda • Objectives • Equipment Protection • Protection Types • Overcurrent Protection • STAR Overview • Features and Capabilities • Protective Device Types • TCC Curves • STAR Short-circuit • PD Sequence of Operation • Normalized TCC curves • TCC Print and Settings Report • Examples and Assignments
3.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Objectives • Human Safety • Prevent injury and fatality
4.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Real Side of Failure in Safety
5.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Objectives • Protection of Equipment • Permit normal operation • Isolate the equipment in case of abnormal conditions
6.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Objectives • Protection of System (Stability Protection) • Over / Under Voltage • Over / Under Frequency • Rate of Frequency Change • Islanding of System
7.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Objectives • Selectivity • Minimal isolation of network with abnormal conditions • Permit normal operation for rest of electrical network
8.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection & Coordination • Objectives • Reasonable Cost • Maximum achievable reliability for protection and coordination at minimal cost • Science, Experience, and Art • Sensitivity to faults and insensitivity to normal operation • Fast fault clearance with proper selectivity • Minimal isolation of faulty area • Capability to operate correctly under all predictable power system conditions
9.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL References • IEEE Std. 242-2001, IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (IEEE Buff Book) • IEEE Std. 141-1993, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants (IEEE Red Book) • IEEE Std. 399-1997, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis (IEEE Brown Book) • Other technical references
10.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Study Procedure • Prepare an accurate one-line diagram (relay diagrams) • Obtain the available system current spectrum (operating load, overloads, fault kA) • Determine the equipment protection criteria • Select the appropriate protective devices / settings • Plot the fixed points (operating/damage curves, FLA, ampacity, etc.) • Obtain / plot the device characteristics curves • Analyze the results
11.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Required Data • One-line diagrams (Relay diagrams) • Power Grid Fault Current Data and Protective Device Settings • Generator Data • Transformer Data • Motor Data • Load Data • Fault Currents • Cable / Conductor Data • Bus / Switchgear Data • Instrument Transformer Data (CT, VT) • Protective Device (PD) Data
12.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection of Equipments • Major Equipments (apparatus) • Induction Motor • Synchronous Motor • Cable • Transformer • Generator • Bus • Transmission/Distribution Line
13.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Equipment Protection Criteria • Permit: Normal Running Condition • Max permitted current at working conditions • Environment temperature, cooling media, elevation, etc. • Protect: Abnormal Fault Condition • Excessive through fault current caused by: • Improper design, installation, or operation of equipment • Incidents
14.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Excessive Currents • Excessive currents in abnormal conditions • Overload current • (100-160% Full Load Amps) • Short-time overload current • (300-1000% Full Load Amps) • Short-circuit current • (300-1200% Full Load Amps)
15.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Capability / Damage Curves t I I2 2 t Gen I2 t Motor Xfmr I2 t Cable I2 t
16.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection Types • Overcurrent • Inverse Time Over Current (TOC) • Instantaneous Over Current (IOC) • Directional • Differential
17.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Protection Types • Impedance • Distance • Voltage • Under/Over Voltage • Frequency • Under/Over Frequency • Mechanical • Pressure (Buchholz Relay)
18.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Overcurrent Protection Overcurrent Characteristics • Inverse Time Over Current (TOC) • Simple, cheap, and large application in LV, and MV • LV Breakers • Represent tolerance band • MCB, MCCB, ICCB, PCB • Fuses • Overload Heater • Overload Relay Time-Current-Characteristics (TCC)
19.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Overcurrent Protection Relay TOC Characteristics Relay TOC Curves • Curve Shape Adaptation • Equipment Protection • Selectivity • Time Margin at higher fault currents
20.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL ETAP Star Overview • Star Mode • Creation of TCC and Star View • Addition of devices to existing TCC • Graphical and Editor adjustments • Star View Options (top) • Combine Curve (ETAP 11 enahncement) • Star Mode and Star View difference
21.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL ETAP Star Overview • Supported Protective Devices and Functions • Overload - CT based & Inline (49) • Phase, neutral, ground, and negative sequence overcurrent (51/50) • Voltage control and restraint overcurrent (51VC/51VR) • Directional overcurrent (67) • High impedance & percentage differential (87) • Electronic & hydraulic reclosers (79) • Relay interlock with HVCB, switch and contactor • CT Ratio and multiple connections • Under / Over Voltage (27/59) *Reverse power (32) and under/over Frequency (81) are supported in Transient Stability
22.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Low Voltage Protective Devices • Low Voltage Circuit Breaker (LVCB) • Power Circuit Breaker (PCB) • UL 1066, ANSI C37.13, ANSI C37.16, ANSI C37.17 • IEC60947-2 • Insulated Case Circuit Breaker (ICCB) • UL489 (Non-fused MCCB, 2 step stored energy closing mechanism, electronic trip, and drawout construction) • IEC60947-2 • Molded Case Circuit Breaker (MCCB) • UL489 (integral unit and enclosed housing of insulating material) • IEC60947-2 • Miniature Circuit Breaker (MCB) • UL489, UL508, UL1077 • IEC60898
23.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL LVCB Differences
24.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Low Voltage Protective Devices • LVCB Trip Units • Thermal Magnetic • Motor Circuit Protector (MCP) • Solid State Trip (SST) or microprocessor based • Electro-mechanical
25.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL LV Protective Devices • MCCB Trip Units – Thermal-Magnetic
26.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL LV Protective Devices • MCCB Trip Units – Magnetic Only
27.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Low Voltage Protective Devices • LVCB Trip Units • Solid State Trip (SST) or microprocessor based • Electro-mechanical • Trip Unit Segments • Long Time (LT ANSI; I> IEC) • Short Time (ST ANSI; I>> IEC) • Instantaneous (IT ANSI; I>>> IEC)
28.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Fuse (Power Fuse) • Non Adjustable Device (unless electronic) • Continuous and Interrupting Rating • Voltage Levels (Max kV) • Interrupting Rating (sym, asym) • Characteristic Curves • Min. Melting • Total Clearing • Application (rating type: R, E, X, …)
29.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Fuse Types • Expulsion Fuse (Non-CLF) • Current Limiting Fuse (CLF) • Electronic Fuse (S&C Fault Fiter)
30.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Minimum Melting Time Curve Total Clearing Time Curve
31.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Current Limiting Fuse (CLF) • Limits the peak current of short-circuit • Reduces magnetic stresses (mechanical damage) • Reduces thermal energy
32.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Current Limiting ActionCurrent(peakamps) tm ta Ip’ Ip tc ta = tc – tm ta = Arcing Time tm = Melting Time tc = Clearing Time Ip = Peak Current Ip’ = Peak Let-thru Current Time (cycles)
33.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL CLF Let-Through Chart
34.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL CLF Let-Through Chart • Assumptions: 1. Short-circuit X/R ≤ Tested Short-circuit X/R, or Short-circuit power factor ≥ tested power factor
35.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL CLF Let-Through Chart • Assumptions 2. The fault is on the load terminal
36.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL CLF Let-Through Chart • Impact of Downstream Breaker • The fault current passing through both PDs • The breaker may start to open representing a dynamic impedance causing reduced let-through current with different trip time • A combination test is needed to make sure this is not happening. This is a series rating test.
37.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL CLF Let-Through Chart • Assumptions 3. The sum of motor full load currents contribution between the series rated devices should not exceeds 1 percent of interrupting rating of lowest rated device.
38.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Symmetrical RMS Amperes PeakLet-ThroughAmperes 100 A 60 A 7% PF (X/R = 14.3) 12,500 5,200 230,000 300 A 100,000 Let-Through Chart
39.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Fuse Generally: • CLF is a better short-circuit protection • Non-CLF (expulsion fuse) is a better Overload protection • Electronic fuses are typically easier to coordinate due to the electronic control adjustments
40.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Zones of Protection • Protective devices and protected equipment represent the “Protection Zone”
41.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Motor Protection • Motor Starting Curve • Thermal Protection • Locked Rotor Protection • Fault Protection
42.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Inrush Current First half cycle current showing current offset. Beginning of run up current showing load torque pulsations. Starting Current of a 4000Hp, 12 kV, 1800 rpm Motor Motor pull in current showing motor reaching synchronous speed
43.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Motor Protection LV Motor Protection MV Motor Protection
44.
© 2011 ETAP.
PROPRIETARY & CONFIDENTIAL Motor Protection • Standards & References • IEEE Std 620-1996 IEEE Guide for the Presentation of Thermal Limit Curves for Squirrel Cage Induction Machines. • IEEE Std 1255-2000 IEEE Guide for Evaluation of Torque Pulsations During Starting of Synchronous Motors • ANSI/ IEEE C37.96-2000 Guide for AC Motor Protection • NEMA MG-1 Motors and Generators • The Art of Protective Relaying – General Electric
45.
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PROPRIETARY & CONFIDENTIAL Overload Relay / Heater • Motor overload protection is provided by a device that models the temperature rise of the winding • When the temperature rise reaches a point that will damage the motor, the motor is de- energized • Overload relays are either bimetallic, melting alloy or electronic
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PROPRIETARY & CONFIDENTIAL Question What is Class 10 and Class 20 Thermal OLR curves?
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PROPRIETARY & CONFIDENTIAL Answer • At 600% Current Rating: – Class 10 for fast trip, 10 seconds or less – Class 20 for, 20 seconds or less (commonly used) – There is also Class 15, 30 for long trip time (typically provided with electronic overload relays) 6 20
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PROPRIETARY & CONFIDENTIAL Answer
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PROPRIETARY & CONFIDENTIAL Overload Relay / Heater • When the temperature at the combination motor starter is more than ±10 °C (±18 °F) different than the temperature at the motor, ambient temperature correction of the motor current is required. • An adjustment is required because the output that a motor can safely deliver varies with temperature. • The motor can deliver its full rated horsepower at an ambient temperature specified by the motor manufacturers, normally + 40 °C. At high temperatures (higher than + 40 °C) less than 100% of the normal rated current can be drawn from the motor without shortening the insulation life. • At lower temperatures (less than + 40 °C) more than 100% of the normal rated current could be drawn from the motor without shortening the insulation life.
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PROPRIETARY & CONFIDENTIAL Motor Starting and Thermal Limit Sample data provided by the manufacturer
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PROPRIETARY & CONFIDENTIAL Motor Protection - Overload Pickup (NEC Art 430.32 – Continuous-Duty Motors) • Thermal O/L (Device 49) Pickup • Motors with marked Service Factor ≥ 1.15 • Pickup = 125% of FLA • Motors with temp. rise not over 40°C • Pickup = 125% of FLA • All other motors • 115% of FLA
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PROPRIETARY & CONFIDENTIAL Motor Protection – Inst. Pickup LOCKED ROTOR S d 1 I X X " PICK UP LOCKED ROTOR I RELAY PICK UP 1.2 TO 1.2 I PICK UP LOCKED ROTOR I RELAY PICK UP 1.6 TO 2 I with a time delay of 0.10 s (six cycles at 60 Hz) Recommended Instantaneous Setting: If the recommended setting criteria cannot be met, or where more sensitive protection is desired, the instantaneous relay (or a second relay) can be set more sensitively if delayed by a timer. This permits the asymmetrical starting component to decay out. A typical setting for this is:
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PROPRIETARY & CONFIDENTIAL Locked Rotor Protection • Thermal Locked Rotor (Device 51) • Starting Time (TS < TLR) • LRA • LRA sym • LRA asym (1.5-1.6 x LRA sym) + 10% margin
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PROPRIETARY & CONFIDENTIAL Fault Protection (NEC Art / Table 430-52) • Non-Time Delay Fuses • 300% of FLA • Dual Element (Time-Delay Fuses) • 175% of FLA • Instantaneous Trip Breaker • 800% - 1300% of FLA* • Inverse Time Breakers • 250% of FLA *can be set up to 1700% for Design B (energy efficient) Motor
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PROPRIETARY & CONFIDENTIAL Low Voltage Motor Protection • Usually pre-engineered (selected from Catalogs) • Typically, motors larger than 2 Hp are protected by combination starters • Overload / Short-circuit protection
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PROPRIETARY & CONFIDENTIAL 200 HP MCP O/L Starting Curve I 2 T (49) MCP (50) (51) ts tLR LRAs LRAasym
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PROPRIETARY & CONFIDENTIAL Low-voltage Motor Ratings Range of ratings Continuous amperes 9-250 — Nominal voltage (V) 240-600 — Horsepower 1.5-1000 — Starter size (NEMA) — 00-9 Types of protection Quantity NEMA designation Overload: overload relay elements 3 OL Short circuit: circuit breaker current trip elements 3 CB Fuses 3 FU Undervoltage: inherent with integral control supply and three-wire control circuit — — Ground fault (when specified): ground relay with toroidal CT — —
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PROPRIETARY & CONFIDENTIAL Minimum Required Sizes of a NEMA Combination Motor Starter System MAXIMUM CONDUCTOR LENGTH FOR ABOVE AND BELOW GROUND CONDUIT SYSTEMS. ABOVE GROUND SYSTEMS HAVE DIRECT SOLAR EXPOSURE. 750 C CONDUCTOR TEMPERATURE, 450 C AMBIENT CIRCUIT BREAKER SIZE FUSESIZE CLASSJ FUSE MOTORHP 460VNECFLC STARTER SIZE MINIMUM SIZE GROUNDING CONDUCTOR FORA50%CURRENTCAPACITY MINIMUM WIRE SIZE MAXIMUM LENGTHFOR1% VOLTAGE DROP NEXT LARGEST WIRE SIZE USENEXT LARGERGROUND CONDUCTOR MAXIMUM LENGTHFOR1% VOLTAGE DROPWITH LARGERWIRE 250% 200% 150% 1 2.1 0 12 12 759 10 1251 15 15 15 5 1½ 3 0 12 12 531 10 875 15 15 15 6 2 3.4 0 12 12 468 10 772 15 15 15 7 3 4.8 0 12 12 332 10 547 20 20 15 10 5 7.6 0 12 12 209 10 345 20 20 15 15 7½ 11 1 12 10 144 8 360 30 25 20 20 10 14 1 10 8 283 6 439 35 30 25 30 15 21 2 10 8 189 6 292 50 40 30 45 20 27 2 10 6 227 4 347 70 50 40 60 25 34 2 8 4 276 2 407 80 70 50 70 30 40 3 6 2 346 2/0 610 100 70 60 90 40 52 3 6 2 266 2/0 469 150 110 90 110 50 65 3 2 2/0 375 4/0 530 175 150 100 125 60 77 4 2 2/0 317 4/0 447 200 175 125 150 75 96 4 2 4/0 358 250 393 250 200 150 200 100 124 4 1 250 304 350 375 350 250 200 250 125 156 5 2/0 350 298 500 355 400 300 250 350 150 180 5 4/0 500 307 750 356 450 350 300 400
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PROPRIETARY & CONFIDENTIAL Required Data - Protection of a Medium Voltage Motor • Rated full load current • Service factor • Locked rotor current • Maximum locked rotor time (thermal limit curve) with the motor at ambient and/or operating temperature • Minimum no load current • Starting power factor • Running power factor • Motor and connected load accelerating time • System phase rotation and nominal frequency • Type and location of resistance temperature devices (RTDs), if used • Expected fault current magnitudes • First ½ cycle current • Maximum motor starts per hour
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PROPRIETARY & CONFIDENTIAL Medium-Voltage Class E Motor Controller Ratings Class El (without fuses) Class E2 (with fuses) Nominal system voltage 2300-6900 2300-6900 Horsepower 0-8000 0-8000 Symmetrical MVA interrupting capacity at nominal system voltage 25-75 160-570 Types of Protective Devices Quantity NEMA Designation Overload, or locked Rotor, or both: Thermal overload relay TOC relay IOC relay plus time delay 3 3 3 OL OC TR/O Thermal overload relay 3 OL TOC relay 3 OC IOC relay plus time delay 3 TR/OC Short Circuit: Fuses, Class E2 3 FU IOC relay, Class E1 3 OC Ground Fault TOC residual relay 1 GP Overcurrent relay with toroidal CT 1 GP NEMA Class E2 medium voltage starter NEMA Class E1 medium voltage starter
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PROPRIETARY & CONFIDENTIAL Thermal Limit Curve
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PROPRIETARY & CONFIDENTIAL Thermal Limit Curve Typical Curve
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PROPRIETARY & CONFIDENTIAL Cable Protection
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PROPRIETARY & CONFIDENTIAL Cable Protection • Standards & References • IEEE Std. 242-2001, IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (IEEE Buff Book) • IEEE Std 835-1994 IEEE Standard Power Cable Ampacity Tables • IEEE Std 848-1996 IEEE Standard Procedure for the Determination of the Ampacity Derating of Fire-Protected Cables • IEEE Std 738-1993 IEEE Standard for Calculating the Current- Temperature Relationship of Bare Overhead Conductors • The Okonite Company Engineering Data for Copper and Aluminum Conductor Electrical Cables, Bulletin EHB-98
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PROPRIETARY & CONFIDENTIAL Cable Protection 2 2 1 t A T 234 0.0297log T 234 The actual temperature rise of a cable when exposed to a short circuit current for a known time is calculated by: Where: A= Conductor area in circular-mils I = Short circuit current in amps t = Time of short circuit in seconds T1= Initial operation temperature (750C) T2=Maximum short circuit temperature (1500C)
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PROPRIETARY & CONFIDENTIAL Cable Short-Circuit Heating Limits Recommended temperature rise: B) CU 75-200C
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PROPRIETARY & CONFIDENTIAL Shielded Cable The normal tape width is 1½ inches
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PROPRIETARY & CONFIDENTIAL NEC Section 110-14 C • (c) Temperature limitations. The temperature rating associated with the ampacity of a conductor shall be so selected and coordinated as to not exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both. • (1) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for Nos. 14 through 1 conductors, shall be used only for conductors rated 60C (140F). • Exception No. 1: Conductors with higher temperature ratings shall be permitted to be used, provided the ampacity of such conductors is determined based on the 6OC (140F) ampacity of the conductor size used. • Exception No. 2: Equipment termination provisions shall be permitted to be used with higher rated conductors at the ampacity of the higher rated conductors, provided the equipment is listed and identified for use with the higher rated conductors. • (2) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than No. 1, shall be used only with conductors rated 75C (167F).
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PROPRIETARY & CONFIDENTIAL Transformer Protection
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PROPRIETARY & CONFIDENTIAL Transformer Protection • Standards & References • National Electric Code 2011 Edition • IEEE Std 242-1986; IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems • C37.91-2000; IEEE Guide for Protective Relay Applications to Power Transformers • C57.12.59; IEEE Guide for Dry-Type Transformer Through-Fault Current Duration. • C57.109-1985; IEEE Guide for Liquid-Immersed Transformer Through- Fault-Current Duration • APPLIED PROCTIVE RELAYING; J.L. Blackburn; Westinghouse Electric Corp; 1976 • PROTECTIVE RELAYING, PRINCIPLES AND APPLICATIONS; J.L. Blackburn; Marcel Dekker, Inc; 1987
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PROPRIETARY & CONFIDENTIAL Transformer Categories ANSI/IEEE C-57.109 Minimum nameplate (kVA) Category Single-phase Three-phase I 5-500 15-500 II 501-1667 501-5000 III 1668-10,000 5001-30,000 IV above 10,000 above 30,000
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PROPRIETARY & CONFIDENTIAL Transformer Categories I, II
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PROPRIETARY & CONFIDENTIAL Transformer Category III
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PROPRIETARY & CONFIDENTIAL Transformer Category IV
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PROPRIETARY & CONFIDENTIAL Transformer t (sec) I (pu) Thermal200 2.5 I 2 t = 1250 2 25Isc Mechanical K=(1/Z) 2 t (D-D LL) 0.87 (D-R LG) 0.58 Frequent Fault Infrequent Fault Inrush FLA
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PROPRIETARY & CONFIDENTIAL Transformer Protection MAXIMUM RATING OR SETTING FOR OVERCURRENT DEVICE PRIMARY SECONDARY Over 600 Volts Over 600 Volts 600 Volts or Below Transformer Rated Impedance Circuit Breaker Setting Fuse Rating Circuit Breaker Setting Fuse Rating Circuit Breaker Setting or Fuse Rating Not more than 6% 600 % 300 % 300 % 250% 125% (250% supervised) More than 6% and not more than 10% 400 % 300 % 250% 225% 125% (250% supervised) Table 450-3(A) source: NEC
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PROPRIETARY & CONFIDENTIAL Recommended Minimum Transformer Protection Protective system Winding and/or power system grounded neutral grounded Winding and/or power system neutral ungrounded Up to 10 MVA Above 10 MVA Up to 10 MVA Above 10 MVA Differential - √ - √ Time over current √ √ √ √ Instantaneous restricted ground fault √ √ - - Time delayed ground fault √ √ - - Gas detection √ - √ Over excitation - √ √ √ Overheating - √ - √
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PROPRIETARY & CONFIDENTIAL Question What is ANSI Transformer Shift Curve?
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PROPRIETARY & CONFIDENTIAL Transformer Shift Factor
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PROPRIETARY & CONFIDENTIAL Dyg Transformer Through Fault
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PROPRIETARY & CONFIDENTIAL Question What is meant by Frequent and Infrequent Faults for transformers?
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PROPRIETARY & CONFIDENTIAL Frequent and Infrequent Faults * Should be selected by reference to the frequent-fault-incidence protection curve or for transformers serving industrial, commercial and institutional power systems with secondary-side conductors enclosed in conduit, bus duct, etc., the feeder protective device may be selected by reference to the infrequent-fault-incidence protection curve. (Frequent Fault = More than 10 through faults (lifetime) for category II and 5 faults for category III) Source Transformer primary-side protective device (fuses, relayed circuit breakers, etc.) may be selected by reference to the infrequent-fault- incidence protection curve Category II or III Transformer Fault will be cleared by transformer primary-side protective device Optional main secondary –side protective device. May be selected by reference to the infrequent-fault- incidence protection curve Feeder protective device Fault will be cleared by transformer primary-side protective device or by optional main secondary- side protection device Fault will be cleared by feeder protective device Infrequent-Fault Incidence Zone* Feeders Frequent-Fault Incidence Zone*
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PROPRIETARY & CONFIDENTIAL Selective Coordination • Inherent Selective Devices • Examples • Differential Relays • Pilot Wire Relays • Transformer Sudden Pressure Relays • More expensive • Justified based on value or role of protected equipment in supply of power
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PROPRIETARY & CONFIDENTIAL Selective Coordination • Overcurrent Selectivity Rules • Downstream device curve is located to the left and below of upstream device curve for range of applicable currents • Sufficient time margin for operation of downstream before upstream
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PROPRIETARY & CONFIDENTIAL Selective Coordination
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PROPRIETARY & CONFIDENTIAL Margins for Selectivity • Relay - Relay coordination requires • Minimum of 0.25 to 0.40 seconds time margin between the relay curves at the maximum fault current to account for the interrupting time of the circuit breaker, relay over-travel time, relay tolerances, and a safety factor • For induction disk relays, the minimum desired time margin for a 5 cycle breaker is generally 0.30 seconds • 5 cycle breaker 0.08 seconds • relay over-travel 0.10 seconds • CT ratio & safety factor 0.12 seconds • Total = 0.30 seconds • For digital relays, the minimum desired time margin for a 5 cycle breaker is generally 0.25 seconds • 5 cycle breaker 0.08 seconds • relay accuracy +.02 sec. 0.04 seconds • CT ratio & safety factor 0.13 seconds • Total = 0.25 seconds • Margin between pickup levels of > 10% for two devices in series.
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PROPRIETARY & CONFIDENTIAL Margins for Selectivity • Electromechanical Relay - Fuse coordination requires a minimum 0.22 second time margin between the curves. • Electromechanical Relay - Low Voltage Breaker coordination requires a minimum 0.22 second time margin between the curves. • Static Relay - Fuse coordination requires a minimum 0.12 second time margin between the curves. • Static Relay - Low Voltage Breaker coordination requires a minimum 0.12 second time margin between the curves. • Fuse - Fuse coordination requires that the total clearing time of the downline fuse curve be less than 75% of the minimum melt time of the upline fuse curve to account for pre-loading. • Fuse - Low Voltage Breaker coordination requires that the down-line breaker maximum time curve be less than 75% of the minimum melt time of the up-line fuse curve to account for pre-loading.
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PROPRIETARY & CONFIDENTIAL Margins for Selectivity • Fuse - Relay coordination requires a minimum 0.3 second time margin between the curves. • Low Voltage Breaker - Fuse coordination requires a minimum 0.1 second time margin between the curves to allow for temperature variations in the fuse. • Low Voltage Breaker - Low Voltage Breaker coordination requires only that the plotted curves do not intersect since all tolerances and operating times are included in the published characteristics. • Low Voltage Breaker - Relay coordination requires a minimum 0.2 second time margin between the curves.
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PROPRIETARY & CONFIDENTIAL Ground Fault Protection • NEC Requirements for Solidly Grounded System • Articles 215.10 (feeders), 230.95 (services), 240.13 (overcurrent protection), etc. • 260 V (150 V, L-G) ≤ Line-Line Voltage ≤ 600 V • Main disconnect is rated 1000 A or more • GF Settings is limited to 1200 A pickup and 1 sec for ground faults > 3000 A • Industry Practice • Grounded wye systems 2400 V or more
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PROPRIETARY & CONFIDENTIAL Ground Fault Detection • General Concept • Measurement of Residual (IR) or Zero Sequence current (3I0) • IR = 3I0 = Ia + Ib + Ic (Vector Summation) • Balanced Fault: Ia = Ib = Ic and IR = 3I0 = 0 • Unbalanced system Ia ≠ Ib ≠ Ic and IR = 3I0 > 0
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PROPRIETARY & CONFIDENTIAL Ground Fault Detection • Direct (Ground, 50G/51G) • Grounded-phase (3I0) current is detected directly with a current transformer installed in the grounded neutral conductor.
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PROPRIETARY & CONFIDENTIAL Ground Fault Detection • Balance Flux (Ground, 50G/51G) (Core Balance or Zero Sequence CT) • Grounded-phase current (IR) is directly detected by a doughnut-type current transformer installed around the three phase conductors Note: The equipment grounding conductors (including conductor shields) must not be installed through the current transformer.
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PROPRIETARY & CONFIDENTIAL Ground Fault Detection • Residual • Grounded-phase current is detected as the unbalance in the current produced by the phase current transformers
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PROPRIETARY & CONFIDENTIAL ETAP Terminology • Relay Ground Function • Externally measured residual current (2 inputs) • Relay Neutral Function • Relay internally measured residual current (6 inputs)
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PROPRIETARY & CONFIDENTIAL Relay Ground Inputs
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PROPRIETARY & CONFIDENTIAL Relay Sensitive Ground Inputs
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PROPRIETARY & CONFIDENTIAL Relay Neutral Inputs
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PROPRIETARY & CONFIDENTIAL Relay Function Diagram
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PROPRIETARY & CONFIDENTIAL Ground Fault Coordination • GF Selective Coordination • Device ground fault overcurrent coordination with: • Other devices with ground detection • Other devices with phase overcurrent detection • Combination of phase and ground fault detection • Minimum and Maximum Fault • Phase and single-line to ground fault coordination
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PROPRIETARY & CONFIDENTIAL Ground Fault Coordination Individual Phase and GF Curves Phase and GF Curve Combination
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PROPRIETARY & CONFIDENTIAL Protective Devices • Relays • Microprocessor/electronic • More expensive, faster, multiple functionality • Electromechanical • Simple, cheap, slower, limited functionality
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PROPRIETARY & CONFIDENTIAL Relay ANSI Device Numbers • 21 – Distance • 27 – Under Voltage • 32 – Directional Power • 49 – Thermal Overload • 50 – Instantaneous Over Current • 51 – AC Inverse Over Current • 52 – AC Circuit Breaker • 59 – Overvoltage • 67 – AC Directional Over Current • 79 – AC Recloser • 81 – Frequency • 87 – Differential • P – Phase • N – Neutral • G – Ground • SG – Sensitive Ground • V – Voltage • VC – Voltage Control • VR – Voltage Restrained
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PROPRIETARY & CONFIDENTIAL Bus Differential Relay
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PROPRIETARY & CONFIDENTIAL Bus Differential Relay • High Impedance Differential • Operating signal created by connecting secondary of all CTs in parallel • CTs must all have the same ratio • Must have dedicated CTs • Overvoltage element operates on voltage developed across resistor connected in secondary circuit • Cannot easily be applied to reconfigurable buses and offers no advanced functionality
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PROPRIETARY & CONFIDENTIAL High Impedance Bus Differential
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PROPRIETARY & CONFIDENTIAL Bus Differential Relay • Percent (Low Impedance) Differential • Relay typically perform CT ratio compensation eliminating the need for matching CTs. • No dedicated CTs needed • Used for protection of re-configurable buses possible
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PROPRIETARY & CONFIDENTIAL Percent Bus Differential
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PROPRIETARY & CONFIDENTIAL Star Normalized View
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