Dual trip coils
Dual trip coils
(OP)
I have a bit of experience in the southern US with industrial and utility power systems, but of late I have had a recurring conversation concerning the employment of dual trip coils on 5-15 kV circuit breakers in industrial environments.
My experience is that they are relatively rare in heavy industry, quite common in utility transmission, relatively rare in utility distribution.
Some of those in my company seem to think they are a good idea. I tend to look at them as an unnecessary complication. I back my position up with the experience of working in dozens of petrochemical and utility facilities. I don't know where they got their position except that they live in fear because of a couple of bad experiences where breakers failed to trip for undisclosed reasons.
I would appreciate comments.
My experience is that they are relatively rare in heavy industry, quite common in utility transmission, relatively rare in utility distribution.
Some of those in my company seem to think they are a good idea. I tend to look at them as an unnecessary complication. I back my position up with the experience of working in dozens of petrochemical and utility facilities. I don't know where they got their position except that they live in fear because of a couple of bad experiences where breakers failed to trip for undisclosed reasons.
I would appreciate comments.
old field guy






RE: Dual trip coils
I guess if they are specified and installed for the right reasons, like in critical utility systems, then they make sense. I have also had a few times when a breaker didn't trip when it was supposed too, in none of those cases a redundant trip coil would have helped. One was a 125 DC supply issue, the others were no maintenance, bad environments and piss poor planning.
My two cents, Mike L.
RE: Dual trip coils
Unless the protection system includes redundant or backup relaying and battery systems, the dual trip coils are probably not adding all that much to the overall reliability. A lot of the new relays can provide monitoring of trip coil continuity,
David Castor
www.cvoes.com
RE: Dual trip coils
RE: Dual trip coils
I don't think I'd be so concerned working in an industrial site or utility distribution, where there isn't the same level of redundancy designed into the rest of the protection system.
RE: Dual trip coils
With the present bunch, it's the same thing. A couple of bad incidents, and even though I can just listen to a cursory retelling of the sad stories and trace the cause to a) poor design and b) poor maintenance, they still go with dual trip coils.
In my former employment with a large electric utility, I was accustomed to dual trip coils on transmission breakers because we also had primary and backup relaying schemes.
I appreciate the input. It assuages my feelings, but I don't think my arguments are going to sway my (non-electrical) project management to change their minds.
old field guy
RE: Dual trip coils
And in the 15kV switchgear feeder breakers for mining application, we specified an undervoltage release device in the CB in addition to the the trip coil. This was mainly for compliance with the mining code as shunt trip is not classified as failsafe.
Not the same as dual trip coils I know. But that's pretty much the most we did to ensure redudant protection against trip coil failure, and this is in addition to trip coil monitoring by the relay.
RE: Dual trip coils
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
RE: Dual trip coils
RE: Dual trip coils
RE: Dual trip coils
(Just my $0.02)
RE: Dual trip coils
Do you know which standards or which voltage levels they are looking at to require redundancy?
We have only been using dual trip coils for about 10 years and there is still internal debate whether the extra complexity is worth it when only one station battery is providing the DC. PRC-005-2 is just one more thing in the minus category.
RE: Dual trip coils
Set one relay 5 cycles slower on phase and the other 5 cycles slower on ground with each relay only tripping one trip coil. Then some times you get a TC1 trip and other times you get a TC2 trip. Or use a latch to alternate which TC gets the trip and which one gets a automatic retrip 3-5 cycles later. One trip, reclose, trip cycle would have both trip coils tripping.
RE: Dual trip coils
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RE: Dual trip coils
I have never encountered an industrial grade 5-15kV circuit breaker with dual shunt trip devices. We even have a customer who has industrial grade, metal enclosed, 38kV vacuum circuit breakers and switchgear. Only single shunt trip devices are used. This experience includes large coal fired power plants, steel mills, paper mills, etc.