Relay Protection 5

[KnicksJets]

Recently we had a lightning event in our plant and although we didn't see any visual signs of damage, we had the unit trip due to operation of a lockout relay. This relay is an elecromechanical relay, not susceptible to seismic events or vibrations. This relay gets input from various other relays such as differentials, overcurrent, pilot wire (PMG-13) etc. None of those relays had flags up suggesting they didn't actuate.
Any theories on why we had the lockout relay actuated? Could inadequate grounding affect the operation of relays such as pilot wire relays (HCB, PMG-13, TR-1 etc) such that they would actuate but the flag not come up?

 

[rbulsara]

I would look harder for the evidence of a relay operation, may be there is a relay with a function that has no flag and self resetting.

I do not see a need to set off on a wild goose chase based on some fancy theories. Rather concentrate energy in reviewing the schematics of the relaying and check everything out.

Rafiq Bulsara

http://www.srengineersct.com

 

[KnicksJets]

One thing we can't afford to do at our site is conduct a wild goose chase with "fancy" theories.
We already looked at all the relay schematic, we even analyzed relay race issues. Unless a flag just didn't drop due to mechanical issues, there is no way the relay actually actuated and the flag didn't come up. These relays were not "Keyed in" they were the initiating cause.

If I have to narrow down the list of my questions, I would ask:
1. Any known report of PMG-13, HV, SAT-1 or CV-8 relay operating but not bringing up flags?
2. How can a poor station grounding cause relay malfunction, specifically relay actuating but flags not dropping?

 

[cranky108]

Some high speed lockouts will operate to fast to allow a flag to fall. So looking harder at the relays is the best avenue to find this.

Pilot wire relay? Like a differential but each half is located in a different location. A spike on an under protected wire is possible. And if I recall some of these have a transfer-trip built in with-out a target.

 

[dpc]

1. The mechanical targets are not 100% reliable. Sometimes they hang up and do not drop.

2. Even electromechanical relays are subject to false operation from vibration. Many a unit has been tripped when someone closes a relay panel door just a little too hard.

3. Radio frequency interference (RFI) can cause false operations of relays, including electromechanical relays. The instantaneous units are fairly susceptible to this. Poor grounding could increase the chances of this occurring, I suppose.

What type of lockout relay?

 

[oldfieldguy]

Make sure your flag units on electromechanical relays are set for the proper current. Many electromechanical relays have flag units with two taps, a higher one, used when tripping circuit breakers, and a lower one, used when tripping auxiliary devices such as the lockout relay. It is not unheard of for the flag unit to fail to drop a flag if it is set on the higher current tap and a low-current device is operated.

old field guy

 

[rbulsara]

Asking if relays had mal-operated, is a very broad question and may not have anything to do with your situation. We do not know the make and model of your lockout relay.

May be a few clarifications would help.

Firstly, why are you saying poor grounding may have something to do with the flag not dropping?

Also what are PMG-13 pilot wires? Why are the related to the lockout relay? What are SAT-1, HV or even CV-8?

What was observed? Which breaker in your system tripped? what was operating? There is no information to go by to offer much here. In the end you will need someone at site to investigate.




Rafiq Bulsara

http://www.srengineersct.com

 

[KnicksJets]

Thanks to most of the folsk who have chipped in with their answers.
For those who are just trying to invalidate my questions than actually help, here are the answers:

Firstly, why are you saying poor grounding may have something to do with the flag not dropping?
Let's take up a case. Station A has one grounding mat and Station B has another. During lightning event, there could be a potential difference causing fault to navigate through a pilot wire scheme due to the difference in grounding. A relay could see it as a fault and flag it; or it could simply misoperate/energize the trip coil but the flag might not come up. Just a hypothesis I was fishing incase some might have seen this. Apparently one plant has seen this kind of event during lightning. Who knew.

Also what are PMG-13 pilot wires? Why are the related to the lockout relay? What are SAT-1, HV or even CV-8?
Assuming that this is NOT a sarcastic question, here goes my response. These are different types of relays, a relay protection engineer will quickly tell you all about them. For example PMG-13 is mainly used for monitoring and transfer tripping. I was wondering if anybody had seen known issues with them energizing but not tripping the flag (or energizing the ICS coil). More on these can be found on ABB.

 

[rbulsara]

Pdshah:
I am not sure why you are taking offense to simple questions. I do not take offense to not knowing your relay models, otherwise I would not have asked! Not everyone knows what you have at your site and not every one works in the exact same industry sector as you are.

I never profess to know everything. But I do know a thing or two about protective relays and lockout relays. You are the one who came here to ask questions. I would not comment further, if you do not want them or share details.

I also tend to agree the folks whose answer you like and those folks indeed are more experienced than I am and asset to this forum.




Rafiq Bulsara

http://www.srengineersct.com

 

[xxjohnh]

Time to update your system and put in fault recording relays. All the devices mentioned are obsolete.You could start by testing all your relays, wonder when they were tested last.

 

[subtech]

oldfieldguy is on the right track. I have dealt with this problem many times. While it is true that many e/m relays have two taps on the target/S.I. unit,(.2 & 2A ?) lockout relays by design are very fast and they require little current to operate. Hence, the current that operates the target on the tripping relay is small, and very short lived. More than once I have seen various e/m relays issue a trip (with the S.I. tap set @ .2 amp) and the target would not drop. We have verified this with detailed testing. It is now policy where I work to shunt all lockout trip coils with a large, relatively low value resistance to ensure that targets operate decisively. Currently, on 125VDC systems, we use 50ohm, 200 watt composition resistors to shunt the lockout coil. We've not had a failure to indicate since we have adopted this policy.

 

[KnicksJets]

Folks thanks for the valuable answers. I liked oldfieldguy and subtech response but thanks to all those who participated.

 

[marks1080]

It doesn't matter if you like an answer or not. The electrons do not care. Find the root cause. If you feel that cannot be done than you need to impliment a way of doing it. Flags are old school and will not give you the entire story. If you are satasfied in accepting an explaination just because it sounds nice or you like it than you are not doing anyone any favours. If no explaination can be given than that should be your answer, along with "update your fault recording..."

Rgds,
Mark