Important Considerations in Testing and Commissioning Digital Relays

Transcription

1 Important Considerations in Testing and Commissioning Digital Relays Drew Welton, Beckwith Electric Co. Inc. Will Knapek, OMICRON electronics Corp. USA

2 Justification Digital technology in protection relays offer many advantages to power systems Extended functionality and options lead to complexity Creates difficulties for relay engineers and technicians to properly test and commission Observations within the industry indicate shortcuts are becoming commonplace Can lead to a false sense of security and ultimately relay misoperation Proper testing is paramount to assure stability and reliability in the protection system Presentation will focus on key elements of proper testing

3 Agenda Pre-Qualification for Proper Testing: 1. Adequate test equipment 2. Understanding the different types of testing First Consideration: Why do we test? 1. Differences in digital vs. EM relays 2. NERC study on relay misoperations Second Consideration: What do we test? 1. Protective elements 2. Logic 3. Communications Third Consideration: How do we test? 1. What to avoid 2. List of do s 3. Proper test sequence examples Fourth Consideration: When do we test? NERC and NETA recommendations 1. Other considerations for test intervals 2. Time vs. maintenance based testing Final Word on Documentation

4 Adequate Test Equipment

5 Adequate Test Equipment Should: Account for all utilized CT and PT inputs simultaneously Have equal or better rated signal accuracy than the protective relay (V, I, F, Phase Angle) Be able to accommodate all utilized binary I/O s simultaneously GPS time synchronization capabilities if required Advanced protocol testing (IEC 61850, 8.1, 9.2) Enough I and V magnitude to reach highest setting for protective elements (50P) Tool up!

6 Evaluation Testing for First-time Installation / Application 6

7 Commission Testing 7

8 Periodic / Maintenance Testing 8

9 First Consideration: Why do we test? EM vs. Digital Relays Calibration: Springs Actuators Contacts Capacitors Resistors Single Element Setting Validation Setting Validation: Configuration Settings Element Settings I/O Mapping Supervision Logic HMI Interface Communications Multiple Elements 9

10 Digital Relay Self-Diagnostics What it covers: Microprocessor hand-shaking ADC Power supply Communication failures Watchdogs Firmware flash failures What it does not cover: Relay contacts Internal CT PT circuits Improper wiring Misapplied logic Incorrect settings In all cases, relay failures covered by self-diagnostics can alert operators through an alarm contact. The relay can then take itself out of service to avoid misoperations. 10

11 First Consideration: Why do we test? Because NERC says so! 11

12 What the NERC Study Tells Us! Communication failure 22% Relay failure / malfunction AC System 14% 14% 10% Other/Explainable 38% Incorrect setting / logic / design errors 2% Unknown NERC 2012 Misoperations Graph 12

13 Second Consideration: What do we test? Secondary CT and PT Wiring 13

14 Protective Elements: 21 Distance Protection 87 Differential 50/51 Overcurrent Fault Types: A-N B-C A-B-C 14

15 Logic Settings Associated with Protective Elements All relevant I/O s associated with each protective element need to be accounted for during the testing process. Both sides of the logic equation should also be tested. 15

16 Additional Relay Logic Examples: Used in both feeder and transmission line protection, disables protective element time delays under certain conditions, such as closing a breaker with a faulted condition. Rather than disable SOTF (Switch-Onto-Fault) during the testing process, proper fault sequences should be applied. Must also create fault conditions that would activate SOTF. 16

17 Programmable HMI s Also Need Testing HMI s can be user defined and must be tested for proper configuration and operation. 17

18 Relay Communications: End to End Testing on a Transmission Line Time Synchronized with GPS Clock 18

19 Third Consideration: How do we test? Thinking logically as to how a relay responds in a faulted condition helps to visualize a proper test sequence. - Drew Welton 19

20 Utilize proper test sequences to avoid associated logic settings: 1. Apply proper pre-fault conditions Nominal V, I 52/a=closed, 52/b=open, contacts in non-faulted state Apply long enough for reset from lockouts if needed 2. Faulted values applied 3. Post-fault State Proper Fault Sequences V, I faulted value removed (I=0), (V=0 or Nominal, location of the PT) Breaker contact status changes (52/a=open, 52/b=closed) Proper fault sequence avoids interference from associated logic SOTF, Breaker Failure, etc. 20

21 Utilize system parameters to simulate true faulted conditions - Real Time Digital Simulations create true fault values and evaluates relay performance - Ignores actual relay settings - Validates that settings have been calculated properly for the application - Can create multiple test scenarios (fault type, location, magnitude) 21

22 Utilize tested object parameters to simulate true faulted conditions - Relay test software allows modeling of a protected object (transformer) - Calculates what the relay settings should be - Validates proper settings and relay operation - Can create multiple test scenarios (fault type, magnitude) 22

23 Modeling parameters for a 2-winding power transformer 23

24 Actual Case Study in Support of Modeling Commissioning Transformer Protection System on a GSU at a Nuclear Facility Method 1: Automated test software reads settings file from the relay Test software applies an automated test for various fault types, magnitudes Test results are all verified, all pass. Method 2: Automated test software requires operator to enter transformer nameplate data Test software uses data to formulate test values, applies automated test for various fault types, magnitudes Test results are all verified, all fail! Cause of the failed test: Improper relay setting in tap calculation! 24

25 Fourth Consideration: When do we test? Time Based Testing What NETA Recommends 25

26 What Determines the Reliability Factor? 1. Criticalness of the protected asset 2. Environmental conditions 3. Redundancy of protection 4. History of failures specific to relay type 5. Robustness of relay design, conformal coating 26

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28 What other conditions would cause us to test an in-service relay? Condition Based Testing 1. Any relay changes to configuration, settings, or logic 2. Firmware updates or changes 3. Questionable or normal operations, critical assets 4. High faulted conditions 5. Change-out of instrument transformers 6. Changes to DC trip circuit 7. Extreme exposure to harsh environmental conditions 28

29 A Final Word for Consideration, Documentation! 29

30 A Final Word for Consideration, Documentation! Modern test sets offer testing software All testing software generates test report documents All relay technicians should have a common system of documentation handling Relay test reports should be systematically archived after review Test reports should be easily retrievable when needed NERC may be here soon, audits are inevitable! 30

31 Questions?