1. Transmission and Generation Misoperations During an Extreme Weather Event

2. Background Information on Hurricane Matthew Event No.1 Event No.2
Agenda
Background Information on Hurricane Matthew
Event No.1
Cause Analysis
Event No.2
Discussion
Conclusion

3. Category 5 hurricane during 2016-2017 hurricane season
Hurricane Matthew
Category 5 hurricane during hurricane season
Category 1 when it made landfall in the Carolinas
Tropical storm-force winds in most of Duke Energy’s eastern territory
Record-breaking rain and flooding (12-16 inches of rain in some areas)
Historic level of impact (58 transmission circuits lost)

4. Line of interest is Line #1-1 between Station 1A and Station 1B.
Event #1
Line of interest is Line #1-1 between Station 1A and Station 1B.
At Station 1A, there is an electromechanical line protection panel.
Station 1A
Line #2-1 G
Station 1B
Station 1C
Line #1-1
Line #3-1

5. LL fault occurred on Line #1-1, between Station 1A and Station 1B.
Event #1
t = 0 seconds
LL fault occurred on Line #1-1, between Station 1A and Station 1B.
Station 1A
Line #2-1 G
Station 1B
Station 1C
Line #1-1
Line #3-1

6. Event #1
t = 0.05 seconds
Breakers at Station 1B trip. They go through a normal reclose cycle and trip out again at t = seconds; fault propagates to 3PH fault.
Line #2-1
Station 1A
Station 1B
Line #1-1
Line #3-1
Station 1C G

7. Event #1
t = seconds
Generator breakers trip due to undervoltage condition on low side bus of the GSU.
Line #2-1
Station 1A
Station 1B
Line #1-1
Line #3-1
Station 1C G

8. Backup protection on Line #2-1 trips.
Event #1
t = seconds
Backup protection on Line #2-1 trips.
Line #2-1
Station 1A
Station 1B
Line #1-1
Line #3-1
Station 1C G

9. Backup protection on Line #3-1 trips.
Event #1
t = seconds
Backup protection on Line #3-1 trips.
Line #2-1
Station 1A
Station 1B
Line #1-1
Line #3-1
Station 1C G

10. Event #1
t = seconds
Fault changes and includes ground current. 67GC relay at Station 1A is able to issue trip and clear the fault.
Station 1A
Line #2-1 G
Station 1B
Station 1C
Line #1-1
Line #3-1

11. Once the fault developed ground current, the 67GC tripped as normal.
Event #1
When the relay panel was investigated at Station 1A, it was found that there was only one line fault detector relay (50L).
The 50L relay was required to assert for any of the phase distance elements to trip.
The relay coil tested as an open circuit and could not assert for a fault. As such, the line effectively had no phase fault protection.
Once the fault developed ground current, the 67GC tripped as normal.

12. Line of interest is Line #1-2 between Station 2A and Station 2B
Event #2
Line of interest is Line #1-2 between Station 2A and Station 2B
At Station 2A, Feeder #1-2 and Line #1-2 can be tied together, and both have electromechanical relay protection.
Station 2A
Line #2-2 G
Station 2B
Station 2C
Line #1-2
Line #3-2
Feeder #1-2
N.O.

13. This was not the intended purpose of the switch.
Event #2
During the event, the switch was mistakenly left closed with the breaker disconnect open, and the feeder breaker was being used to back up the line.
This was not the intended purpose of the switch.
Station 2A
Line #2-2 G
Station 2B
Station 2C
Line #1-2
Line #3-2
Feeder #1-2
N.O.

14. LL fault on Line #1-2 between Station 2A and Station 2B.
Event #2
t = 0 seconds
LL fault on Line #1-2 between Station 2A and Station 2B.
Relays at Station 2B detect fault, trip, reclose, and trip out again as designed.
Station 2A
Line #2-2
Station 2B
Line #1-2
Line #3-2
N.O. G
Feeder #1-2
Station 2C

15. Undervoltage condition causes generation facility to trip.
Event #2
t = 1.2 seconds
Undervoltage condition causes generation facility to trip.
Station 2A
Line #2-2
Station 2B
Line #1-2
Line #3-2
N.O. G
Feeder #1-2
Station 2C

16. Reverse-looking backup protection successfully clears fault.
Event #2
t = 1.5 seconds
Reverse-looking backup protection successfully clears fault.
Station 2A
Line #2-2
Station 2B
Line #1-2
Line #3-2
N.O. G
Feeder #1-2
Station 2C

17. The Zone 1 phase relay for the feeder could not see the fault.
Event #2
Since the station was left in an abnormal configuration, the feeder relays were responsible for protection.
The Zone 1 phase relay for the feeder could not see the fault.
The Zone 2 phase relay output contacts had developed resistance between them.
Even though the Zone 2 relay detected the fault and successfully closed the contacts, the contacts couldn’t transmit the signal successfully.

18. The history behind each event
Discussion
The history behind each event
Event No.1: Original station design only had one set of CTs on the breaker available for the line protection panel.
Event No.2: The intent was for the line to back up the feeder, not to have the feeder back up the line.
How are these events different?
Event No.1 is a true single point of vulnerability.
Event No.2 is murkier. There was a single point of vulnerability, but only in the abnormal arrangement.
Different types of relays (50L vs. 21P).
How are these events similar?
Electromechanical panels.
Caused by a single relay failure.
Trip failure exacerbated by the weakened system (why we lost generation).

19. Event No.2 would not have occurred if:
Discussion
Neither of these events would have occurred with DEP’s standard microprocessor panel.
Event No.1 would not have occurred if single point of vulnerability had been addressed when the breakers were replaced.
Event No.2 would not have occurred if:
The station had been in its normal arrangement.
The station had been set up with the line protecting the feeder.
The panel had been designed with the intent of protecting the line.
The idea that an electromechanical panel inherently has more redundancy than a microprocessor panel is not true.

20. Number of relay failures to lose protection for: Forward Phase Faults
Discussion
Number of relay failures
to lose protection for:
Forward Phase Faults
MP: 2
EM: 2
Forward Ground Faults
EM: 1 or 2
Reverse Phase Faults
EM: 1 or 0
Reverse Ground Faults
EM: 0
Number of relay failures
to lose protection for:
Forward Phase Faults
MP: 2
EM: 1
Forward Ground Faults
EM: 1 or 2
Reverse Phase Faults
EM: 1 or 0
Reverse Ground Faults
EM: 0
Line Prot 1
Line Prot 2
BF / CTRL
DEP Microprocessor Panel
21-1
21-2
21-3R
21-3F
21-C
67G
67GC
50L
21-X
DEP Electromechanical Panel
50L-2

21. Conclusion
When upgrading station equipment, it is important to see if the previous design left single points of vulnerability and address them if you can.
Electromechanical relay panels do not inherently provide more redundancy.
Single points of vulnerability are not just limited to the relays on the panel; abnormal system arrangements can create them.

22. Special Thanks To
Al Ward
Mark Matthews
Rod Smith
John O Connor