Relaying 101. by: Tom Ernst GE Grid Solutions

Transcription

1 Relaying 101 by: Tom Ernst GE Grid Solutions

2 Relaying 101 The abridged edition

3 Too Much to Cover Power system theory review Phasor domain representation of sinusoidal waveforms 1-phase and 3-phase power Symmetrical components Zones of protection Relaying principals Over-current Differential Distance Page 3

4 Power system theory review Phasor domain representation of sinusoidal waveforms Vectors: multi-dimensional, static N Duluth St Paul E Page 4

5 Power system theory review Phasor domain representation of sinusoidal waveforms Phasors: multi-dimensional, time-variant, rotate at constant angular velocity (ω=2πf) Projection onto the Re axis plots as cos(ωt+θ) Projection onto the Im axis plots as sin(ωt+θ) m*cos(ωt+θ) => θ => r e + ji m where M=m/ 2 (RMS value) j operator = 90 degree phase shift Useful for showing lead/lag relationships M leads N by (θ+φ) i m Im M(ω) ω φ θ r e Re Page 5 N(ω)

6 Power system theory review 1-phase power Ohms law: V=I*Z (time or phasor domain) S=V*I * =p+jq (V and I are phasors, S is a vector) S=V*(V/Z) * ; S = V 2 /Z S=I*I * /Z ; S = I 2 Z Power factor pf = p/s = cos(θ) for pure sinusoids Leading/lagging (current relative to the voltage) Ppage 6

7 Power system theory review Balanced 3-phase power Phase quantities are equal magnitude and 120 o displaced AB = 3* A BC C CA A AB=A-B -B B AB Page 7

8 Power system theory review 3-phase power Ohms law: V PN =I P *Z PN S 1P =V PN *I P * S 3P =S A +S B +S C For balanced systems: S 3P = 3*S 1P S 3P = V PP 2 /Z PN Z PN = V PP 2 /S 3P = V PN 2 /S 1P I P = S 3P /( 3*V PP ) Page 8

9 I ll try to keep this simple. Hopefully, most of it will be correct!

10 Power system theory review Symmetrical components Mathematical trick for unbalanced systems Superposition theorem Break original system into 3 balanced sub-systems Positive sequence (phase rotation same as original) Negative sequence (phase rotation opposite of original) Zero sequence (no phase rotation) Perform balanced analysis on each sub-system and then add the results to get the total Page 10

11 Power system theory review Symmetrical components Definition: V A =V A1 +V A2 +V 0 + V B =V B1 +V B2 +V 0 V C =V C1 +V C2 +V 0 V A +V B +V C = 3V 0 I A =I A1 +I A2 +I 0 + I B =I B1 +I B2 +I 0 I C =I C1 +I C2 +I 0 I A +I B +I C = 3I 0 Page 11

12 Power system theory review Symmetrical components C1 B1 A1 ω A2 ω C2 B2 Negative seq (ACB) ω A0=B0=C0=0 Zero seq A Positive seq (ABC) A=A1+A2+0 Page 12

13 Power system theory review Symmetrical components C1 A1 B1 Positive seq (ABC) A2 C2 B2 Negative seq (ACB) A0=B0=C0 Zero seq A B=B1+B2+0 B Page 13

14 Power system theory review Symmetrical components C1 A1 B1 Positive seq (ABC) A2 C2 B2 Negative seq (ACB) A0=B0=C0=0 Zero seq A C C=C1+C2+0 B Page 14

15 Power system theory review Symmetrical components C1 A1 B1 Positive seq (ABC) A2 B2 C2 Negative seq (ACB) Phase system rotation is ABC A0=B0=C0=0 Zero seq A ω C B Page 15

16 Power system theory review Symmetrical components Physical meaning (intuition) Positive sequence is normal balanced system Zero sequence is ground current Negative sequence creates reverse rotating fields in motors and generators Slip frequence = 2*f Rotor is cutting many lines of force Induces heating in the rotor Phase-phase unbalances/faults create negative sequence Phasae-ground unbalances/faults create zero sequence Page 16

17 Relaying: An addiction that is hard to break!

18 Zones of Protection Goals of protective systems Detect and isolate all faults (reliability) Never mis-operate (security) Isolate the minimum amount of equipment Time is of the essence Some protection systems operate to prevent a fault (ex: overload) Requires selectivity Each protection device is assigned a zone of protection Page 18

19 Zones of Protection T-Line 52 Bus Highly selective Over-lapping Back-up blurs the zone boundaries What breakers are tripped for each zone? 52 Trans Bus Page 19 Radial Fdr Radial Fdr Radial Fdr

20 Relaying principals Over-current relaying Instantaneous (50) Definite time Time (51) Phase Neutral/Ground (zero sequence) Directional (67) Page 20

21 CHOICES, CHOICES, CHOISES...

22 Instantaneous over-current element (50) Instant. Relay CTR=400/5 Inst.=5000A Is this really instantaneous? S E C O N D S No Operate Operate No intentional delay CURRENT (A).01 Page 22 TIME-CURRENT Voltage 13.8 kv By TWE For Instantaneous Over-current relay Characteristic No. M2008 Comment Date 11/6/2008

23 Instantaneous over-current element with definite time delay (50) S E C O N D S No Operate Instant. Relay CTR=400/5 Inst.=5000A Second intentional delay Operate CURRENT (A).01 Page 23 TIME-CURRENT Voltage 13.8 kv By TWE For Definite Time Over-Current Relay Characteristic No. M2008 Comment Date 11/6/2008

24 Time over-current element (51) Why do we use this inverse time characteristic? S E C O N D S (Extreemly Inv) UR-IEEE-EI TD=2.000 CTR=400/5 Pickup=5.A No inst. TP@2=19.043s (Moderatly Inv) UR-IEEE-MI TD=2.000 CTR=400/5 Pickup=5.A No inst. TP@2=7.6065s (Very Inv) UR-IEEE-VI TD=2.000 CTR=400/5 Pickup=5.A No inst. TP@2=14.055s CURRENT (A).01 Page 24 TIME-CURRENT Voltage 13.8 kv By TWE For Time Over-current Relay Characteristics No. M2008 Comment Date 11/6/2008

25 Combined instantaneous and time over-current element (50/51) /51 UR-IEEE-EI TD=2.000 CTR=400/5 Pickup=5.A Inst=5000A TP@2=19.043s S E C O N D S Page CURRENT (A) TIME-CURRENT Voltage 13.8 kv By TWE For Time Over-Current Relay With Instantaneous Characteristic No. M2008 Comment Date 11/6/

26 Phase (50/51P) and Neutral (50/51N) overcurrent elements (composite coordination) /51P UR-IEEE-EI TD=2.000 CTR=400/5 Pickup=5.A Inst=5000A TP@2=19.043s 2. 50/51G UR-IEEE-MI TD= CTR=400/5 Pickup=2.A Inst=5000A TP@2=45.639s Page 26 Why can the neutral pick-up be set less than full load? Time coordination is achieved through selection of curve shapes, pick-ups and time delays. S E C O N D S Full Load CURRENT (A) TIME-CURRENT Voltage 13.8 kv By TWE For Phase and Ground Over-current Relay Characteristics No. M2008 Comment Date 11/6/

27 Relaying Principals Directional Relay (67) Compares angle between operating and polarizing quantities Operating = line current Polarizing = something stationary Healthy phase-phase voltage Sequence voltage Sequence current 67 Page T-Line 1 Bus 52 T-Line T-Line 3 52

28 Relaying principals Bus differential relay (87B) Kirchhoff's current law I 1 + I 2 = I 3 87B I I 2 Bus 52 I 3 Page 28

29 Relaying principals Bus differential relay (87B) CT error will cause operating current Poor quality CTs CT saturation due to very high fault currents Use percentage slope characteristics for security Operate on difference current Restrain operation with through-load current Minimum operating current = I rest * Slope Minimum pick-up to avoid divide by zero issues Directional element and CT saturation detection add security Will not operate for faults outside the zone of protection No coordination required Page 29

30 Bus differential relay slope characteristic TRIP Slope 2 = 80% TRIP Region Minimum Pick-up = 0.1 pu Slope 1 = 25% NO TRIP Page 30

31 Relaying principals Transformer differential relay (87T) Same principal as bus except S IN = S OUT Account for turns ratio and phase shifts Includes additional restraint 2 nd harmonic for in-rush 5 th harmonic for over-excitation May include: directional element CT saturation detection 52 S IN 87T S OUT Page 31

32 Relaying principals Line differential relay (87L) Same principal as bus: I S = I R Account for CT ratio differences Uses magnitude and angle of differential and restraint May include differential for line termination transformer Requires high bandwidth communication channel Fiber Digital microwave Digital radio Page 32 87L 87L Conn Chan Line I S I R

33 Relay Engineers get used to the abuse, Given enough time...

34 Relaying principals Distance relay (21) AKA: Impedance Measures the complex impedance to the fault Z=V/I Operates instantaneously if Z is within the characteristic Offset MHO Quadrilateral T-Line 1 Page 34

35 Offset MHO Characteristic jx Desired line angle line 21 R Operating Voltage = V-I*Z R Polarizing Voltage = V Most fault impedances are on or near the line angle Page 35

36 Quadrilateral Characteristic jx Desired line angle line 21 R Most fault impedances are on or near the line angle Page 36

37 Relaying principals Distance relay (21) Uses pre-fault memory voltage for directional control on zero-voltage faults Phase Phase-phase element 3-Phase element Phase or sequence component based Ground Measures positive sequence impedance Uses a K 0 scaling factor to approximate zero sequence impedance Page 37

38 Relaying principals Distance relay (21) Typically applied using stepped zones Zone 1 (21-1) under-reaching: Z R =85% of Z L Instantaneous Zone 2 (21-2 ) over-reaching: Z R =125% of Z L Time delayed to coordinate with remote zone 1 elements T-Line 1 Page 38

39 Relaying principals Pilot schemes (communication assisted) Permissive over-reaching transfer trip (POTT) Send permission to remote end(s) if 21-2 operates Local instantaneous trip if 21-2 operates while receiving permission from remote end(s) 21-2 Trip zone T-Line 1 Page 39

40 Relaying principals Pilot schemes (communication assisted) Directional comparison blocking (DCB) Send block to remote end(s) if 21-R operates Local instantaneous trip if 21-2 operates while not receiving block from remote end(s) R Trip zone 21-R T-Line 1 Page 40

41 Relaying principals Pilot schemes (communication assisted) Direct under-reaching transfer trip (DUTT) Local instantaneous trip if 21-1 operates Send direct transfer trip to remote end(s) if 21-1 operates 21-1 Trip zone T-Line 1 Page 41

42 Lots More to Talk About Generator protection Motor protection Capacitor bank protection and control Reactor protection Over-voltage coordination IEC Save it for Relaying 102, 103,... Page 42

43 It s finally over! Time to grab a beer.

44 Thanks for Your Time! Any Questions? Page 44