Transformer protection IED RET 670

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Ferdinand Norris
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1 Gunnar Stranne Transformer protection IED RET 670 Santiago Septiembre 5,

Transformer protection IED RET670 2 Introduction features and applications Differential protection functions Restricted Earth Fault protection function

2 Transformer protection IED RET670 2 Introduction features and applications Differential protection functions Restricted Earth Fault protection function High Impedance Differential protection function Some additional functions and application examples Preconfigured ready-made packages Summary and conclusions

3 Benefits of RET670 outstanding features Half cycle operating time a new performance standard! One or two differential functions Differential function compensated automatically for tap changer position for improved sensitivity An additional sensitive and fast differential function based on negative sequence current - ~1% sensitivity High impedance or low impedance restricted earth-fault differential protection for each winding Possibility to use multi - CT arrangements for increased differential protection stability Tap changer control 3 Breaker control, measuring, monitoring and recording

4 Applications Power transformers, including autotransformers, reactors and generator transformer blocks Two or three vector group (or winding) transformers Single- or multi circuit breaker arrangements Up to six stabilized 3-phase current inputs 4

5 Three-winding Transformer Three-winding variant up to 6 restraint three-phase CT inputs Ensures enhanced throughfault stability for multibreaker arrangements Tap changer control 5

6 Auto Transformer Phased segregated biased differential protection for Autotransformers in 1½ CB applications Serial and common windings Up to 4 three-phase CT inputs 6

Phase Shifting Transformer Transformer key data 1400 MVA 400/ 400 kv +-25 1200 tons 32 MUSD contract 7 Project aspects Cooperation between

7 Phase Shifting Transformer Transformer key data 1400 MVA 400/ 400 kv tons 32 MUSD contract 7 Project aspects Cooperation between End User, Relay Manufacturer & PST Manufacturer is of outmost importance Cooperation required in the very early design stage of the project

Shunt Reactor Protection And Control Protection Phase segregated biased differential protection High-impedance differential protection

8 Shunt Reactor Protection And Control Protection Phase segregated biased differential protection High-impedance differential protection Over/under-voltage protection Switching control for lines and busses 8 RET 670 is optimized for each application with maximum reliability and short operating time

9 Step-up Transformer In Power Stations Overall differential protection of a generator transformer unit Differential protection for the step-up transformer and/or the auxiliary transformer Back-up protection functionality 9

10 Complementary Protection Functions Full scheme distance Overcurrent 19 inverse Thermal overload Breaker failure Voltage functions with high reset ratio 10 RET 670 fits all power system elements that require unit and additional protection functionality

11 Differential Protection Two-winding or three-winding functions Two-winding variant up to 4 three-phase CT inputs Enhanced through-fault stability for multi-breaker arrangements Three-winding variant up to 6 three-phase CT inputs Enhanced through-fault stability for multi-breaker arrangements 11

12 Transformer Protection Terminal Differential Protection of 2- winding Power Transformers 2- winding power transformer 2- winding power transformer with unconnected delta tertiary winding 2- winding power transformer with 2 circuit breakers on primary side 2- winding power transformer with 2 circuit breakers on secondary side 12 - winding power transformer with 2 circuit breakers on both sides

13 Transformer Protection Terminal Differential Protection of 3- winding Power Transformers 3- winding power transformer with all 3 windings connected 3- winding power transformer with 2 circuit breakers on (any) one side, (e.g. 2 parallel power lines on one side) winding power transformer with 2 circuit breakers on 2 out of 3 sides, (e.g. a meshed power network) Note! Also 3-out of 3 with 2 breakers is possible.

14 Differential Protection A differential current does not always mean there is a fault in the transformer Inrush current in power transformers Saturation of current transformers Overexcitation Tap changer position etc. Means of coping with these situations must be included in the design 14

15 Differential Protection Ability is included to handle two tap changers, i.e. one tap changer per winding on any two windings Functionality Three-section settable restrain characteristic High set unrestrained operation Idiff Idunre Unrestrained operation operate 1.0 pu Idmin 1.25 pu restrain Ibias 15

Transformer Inrush Current Stabilization Second harmonic stabilisation Wave form stabilisation wave block CT saturation cause a second harmonic component in the secondary current 16 Transformer

16 Transformer Inrush Current Stabilization Second harmonic stabilisation Wave form stabilisation wave block CT saturation cause a second harmonic component in the secondary current 16 Transformer inrush currents contain a percentage of second harmonic current. This is used for discrimination but second harmonic blocking normally causes delayed operation in case of CT saturation. It is also possible to monitor the shape of the differential current signal. The low-current gap measurement indicates inrush.

17 Transformer Inrush Current Stabilisation Internal fault followed by CT saturation Delayed trip of the restrained differential function due to the traditional use of second harmonic blocking (Set level 15 %) 17

18 Overvoltage Stabilization The fifth harmonic component is used for stabilization Magnetizing current at system overvoltage i L1 i L2 i L The fifth harmonic component appears as a characteristic quantity in the transformer magnetizing current during overvoltage.

19 Differential Protection DIFP- application 19 Two- and three winding applications Stabilization of up to 6 inputs Inrush current stabilization Second harmonic Waveform Phase segregated Selectable Cross-blocking 5th harmonic stabilization at overvoltage Sensitivity influenced by tap changer position (selectable) Selectable subtraction of zero sequence currents

20 Differential Protection Blocking condition: 2 nd harmonic, 5 th harmonic waveblock, cross block & Neg Seq Int / Ext Fault Discriminator internal sensitive & restrained unrestrained 1 TRIP START 20

21 Differential Protection Testing RET670 for maximum performance Fault detection in 7 ms! 21

22 Negative sequence current differential function Internal / external fault discriminator Based on the measurement of negative sequence current 22

23 Negative sequence current differential function Before comparison, all negative sequence currents are compensated for turns ratio and vector group phase displacement External fault: 180 relative phase displacement Internal fault: 0 relative phase displacement IminNegSeq 2% - 20% Default 4% 23 NegSeqROA Default 60

24 Negative sequence current differential function An internal fault with heavy CT saturation Directional Comparison Criterion: Internal fault as seen from the HV side ms 60 excursion from 0 degrees due to CT saturation definitely an internal fault 24 external fault region ka 1.0 ka 1.5 ka HV side contribution to the total negative sequence differential current in ka Directional limit (within the region delimited by ± 60 degrees is internal fault) trip command in 12 ms Internal fault declared 7 ms after internal fault occurred

Negative Sequence Differential Protection An internal small transformer interturn fault was cleared by Buckholz relay and existing differential protection failed to detect fault

Criterion: Internal fault as seen from the HV side 150 210 120 20 A 90 8 19 10 180 0 30 A 60 (negseqroa = ± 60 deg) 30 330 steady-state position for this internal fault Internal

25 Negative Sequence Differential Protection An internal small transformer interturn fault was cleared by Buckholz relay and existing differential protection failed to detect fault Test of RET 670 with recorded signals proved successful If one or the other of currents is too low, then no measurement is done External fault region Directional Comparison Criterion: Internal fault as seen from the HV side A A 60 (negseqroa = ± 60 deg) steady-state position for this internal fault Internal fault declared 12 ms after fault A 50 A Contribution to total neg. seq. diff. current from HV side (in A) Directional limit (within ± negseqroa degrees is internal fault)

26 26 Negative sequence current function - summary Fast operating times half cycle Start from ordinary differential protection required, but blocking conditions are bypassed Sensitive negative sequence protection Gives sensitive turn-to-turn fault protection The trip request must be confirmed several times in succession before the final trip request is placed this security feature causes an increase in the operating time The operating time is about 30ms for very lowlevel turn-to-turn faults This sensitive negative sequence protection is blocked for high fault current conditions

27 Restricted Earth Fault Protection diff current in pu Operate characteristic minimum base sensitivity 50 % default base sensitivity 30 % maximum base sensitivity 5 % Step : 1 % transformer rated current pu bias current in per unit

28 Restricted Earth Fault Protection Internal fault External fault zone of protection zone of protection I L1 I L1 I L2 I L2 I L3 I L3 3I 0 I N I FAULT I I FAULT N 3I 0 I N I N internal fault external fault 3I 0 MTA ROA reference is neutral current MTA ROA 3I 0 operate for internal fault ROA -I N restrain for external fault operate for internal fault ROA -I N restrain for external fault reference is neutral current 28

29 Differential Protection 29 Switch-on-to-fault Built-in logic to improve operating speed for switch-on-to-fault condition Possible to record the differential currents and/or bias current by the disturbance recorder channels Differential currents Instantaneous or RMS Bias current RMS

30 Restricted Earth Fault Protection 3I0 < 3% of Ibase I N > 50% of Idset Directional check 1 1 TRIP START 30

31 Restricted Earth Fault Protection Up to 4 three-phase CT inputs makes it possible to handle autotransformers in 1½ CB applications Enhanced function for autotransformer applications I1 I2 I3 I3P I1 I2 I3 I1 I2 I3 I3P I3P REFx I1 I3PRI1 I3PRI2 I3SEC1 I3SEC2 I I1N 31

32 Restricted Earth Fault Protection 32 Switch-on-to-fault Built-in logic to improve operating speed for switch-on-to-fault condition Possible to record differential currents and/or bias current by the disturbance recorder Differential currents Instantaneous or RMS Bias current RMS

33 High Impedance Differential Protection Three instances 1 or 3 high impedance differential External stabilizing resistors & metrosils are used Typical applications High impedance REF Restricted Earth Fault protection Tee - feeder differential protection Bus differential 33

34 Overexcitation Protection V/Hz measurement Positive sequence or single phase-to-phase voltage Transformer magnetic core cooling time constant setting IEEE inverse time and User defined trip curves available Alarm level as percentage of trip level 34

35 Thermal Overload protection function 49-1 Ith 86/94 I->O 49-1 Ith Two thermal overload functions Tripping of load will give cooling chance to restore normal temperatures. Settable thermal time constants for short circuits and low overloads Measures RMS current Lockout reset level (in % of heat content trip value) 86/94 I->O Alarm levels 1 and 2 (each in % of heat content trip value) 35

36 TOF/TUF/RVF(df/dt) Frequency Protection Over-frequency and under-frequency Six steps OF & UF settable frequency and time delay Measures Ph-Ph or Positive sequence voltage Under-voltage blocking Df/dt with positive or negative derivative setting High accuracy Short operating time Accuracy 2 mhz for three phase Accuracy 10 mhz for single phase 36 Voltage dependent tripping time possible!

37 Frequency Protection - Applications Under frequency 37 Load shedding systems Remedial action schemes Over frequency Generation shedding Remedial action schemes Rate-of-change of frequency Generation shedding Load shedding Remedial action schemes

Six Pre-configured RET 670 - Ready To Use RET 670-A30 Two winding transformer, single circuit breaker RET 670-B30 Two winding transformer, multi circuit breaker (1½ CB or double CB on either, or

38 Six Pre-configured RET Ready To Use RET 670-A30 Two winding transformer, single circuit breaker RET 670-B30 Two winding transformer, multi circuit breaker (1½ CB or double CB on either, or both, sides of the transformer) RET 670-A20 Three winding transformer, single circuit breaker RET 670-A31 Three winding transformer, single circuit breaker, current and voltage inputs RET 670-A40 Three winding transformer, single circuit breaker (1½ CB or double CB on any, or all, sides of the transformer) RET670 B40 Three winding transformer, multi circuit breaker (1½ CB or double CB on any, or all, sides of the transformer) 38

39 Two Winding Transformer Single Circuit Breaker DR 50BF 3I>BF 50/51-1 3I> 86/94 I->O RET 670-A30 81O/81U f</> O5 51N-1 I 87N-1 Ind> 87T 3Id/I> 52PD PD 24 U/f> O4 87N-2 Ind> 59N UN 59N UN 51N-2 I 59 3U> 27 3U< O2 60 FF 50BF 3I>BF 90 VCTR 50/51-2 3I> 86/94 I->O 21 Z< O1 25/27 SC/VC 60 FF 59 3U> 27 3U< DR Contr Interl O3 39

40 Two Winding Transformer Multi Circuit Breaker 50BF 3I>BF 60 FF 25/27 SC/VC 60 FF 50BF 3I>BF 51N-1 I 50BF 3I>BF Σ DR 50/51-1 3I> 87N-1 Ind> 87T 3Id/I> 87N-2 Ind> 59N UN 51N-2 I 50/51-2 3I> 59 3U> 86/94 I->O 86/94 I->O 81O/81U 2* f</> O8 52PD PD 24 U/f> 50BF 3I>BF 59N UN 59 3U> 27 3U< 21 Z< 27 Contr 3U< Interl DR RET 670-B30 2* 2* 25/27 SC/VC O7 O6 O4 O5 O2 O1 O3 40

41 Three Winding Transformer Single Circuit Breaker 51N-1 I DR 50BF 3I>BF 50/51-1 3I> 87N-1 Ind> 87T 3Id/I> RET 670-A20 86/94 I->O 60 FF 25/27 SC/VC 24 U/f> 51N-3 I 87N-3 INd> O6 O4 O5 87N-2 Ind> 59N UN 50BF 3I>BF 50/51-3 3I> 59N UN 51N-2 I 59 3U> 27 3U< O2 60 FF 25/27 SC/VC 60 FF 50BF 3I>BF 50/51-2 3I> 59 3U> 27 3U< DR 86/94 I->O 86/94 I->O 21 Z< Contr Interl 81O/81U f</> 52PD PD O1 O3 O7 41

42 Three Winding Transformer Multi Circuit Breaker 50BF 3I>BF Σ DR 50BF 3I>BF 50/51-1 3I> RET670 B40 86/94 I->O 81O/81U f</> 52PD PD 60 FF 25/27 SC/VC O7 O8 O6 50BF 3I>BF 50/51-3 3I> 60 FF 25/27 SC/VC 60 FF 51N-1 I 50BF 3I>BF 87N-1 Ind> 87T 3Id/I> 87N-2 Ind> 59N UN 51N-2 I 50/51-2 3I> 59 3U> 27 3U< DR 86/94 I->O 86/94 I->O 24 U/f> 51N-3 I 87N-3 INd> 59N UN 59 3U> 27 3U< 21 Z< Contr Interl O4 O5 O2 O1 O3 42

Benefits of RET670 Functional flexibility Every step you take - ABB has the solution 43 Configuration flexibility High performance User friendly Pre-defined packages IED 670 series member means; Less

43 Benefits of RET670 Functional flexibility Every step you take - ABB has the solution 43 Configuration flexibility High performance User friendly Pre-defined packages IED 670 series member means; Less spare parts needed Simplified engineering and maintenance Common look and feel and common tools Extensive Self-supervision Remote communication flexibility Easy integration in Substation Automation Systems

44 Benefits of RET670 outstanding features 44 Fast, sensitive and secure differential function tap-changer compensated Fast and sensitive negative sequence differential function -> half cycle operation Multi-CT inputs increases security and functionality High or low impedance restricted earthfault winding differential funcions Extensive function library and options Up to 12 general I -V functions; distance and extra differential functions High reset voltage functions Extendable analog and digital I/O Full control functionality Large HMI option

45 Potencia y productividad para un mundo mejor

Transformer Fault Categories

Transformer Fault Categories 1. Winding and terminal faults 2. Sustained or uncleared external faults 3. Abnormal operating conditions such as overload, overvoltage and overfluxing 4. Core faults 1 (1)