Do we still need tripping relays
Do we still need tripping relays
(OP)
hi every one,
my question is as in the subject, do we still need to add stand-alone tripping relays?
what is your practice?
thank you,,
my question is as in the subject, do we still need to add stand-alone tripping relays?
what is your practice?
thank you,,






RE: Do we still need tripping relays
From my point of view: NO.
And stand alone LOR also don't need.
BUT, you must check CB trip current and make/break current of your relay ( numerical)
Regards.
Slava
RE: Do we still need tripping relays
slavag, interesting point about break current ratings, most companys I asked a few years ago said welded contacts and burned up trip coil is part of a failed breaker.
Have you looked at solving the breaker failure welded contacted issue?
RE: Do we still need tripping relays
If by tripping relay you mean an interposing aux relay between the protective relay and the breaker trip coil, then those may not be needed if the protective relay has good output contacts and if you can get the quantity you need. But keep in mind that the most common failure in digital relays is the output contact. You should use surge suppression on the relay output contacts, especially when going directly to a breaker trip coil.
RE: Do we still need tripping relays
My favorite GE "UR" series relays have provision for output contacts to "seal in" until the current through them is interrupted by auxiliary contacts as the breaker opens.
I would be more nervous about the ratings of these output contacts if I was interfacing them with older breakers that had higher trip current requirements, but I am fortunately dealing with more modern vacuum circuit breakers with much lower current requirements.
Still, though, today's "30 amp rated" contact is a lot smaller than the 30 amp contact of years gone by, and that's a niggling concern in my mind.
old field guy
RE: Do we still need tripping relays
But please see below what my army sergeant said ! Let's not to forget about possible circuit breaker failure or short circuit in trip circuit cable (I had such case).
When the price is not the main concern it is better (acc. to me) to use external relay to be on safe side. It is easier to replace electromechanical relay or even just to change wiring to spare healthy contact instead of sending expensive relay protection for repair.
If the high price of fast tripping relay is a problem, I have seen alternative solution: Relay protection trips directly circuit breaker and via second contact energizes coil of cheap auxiliary contactor. Heavy duty contact of the contactor closes in parallel of relay protection trip contact. It is clear that in case of CB failure current through tripping coil will be broken by the contactor, not by relay protection. Not bad solution, I would say.
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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: Do we still need tripping relays
Situation YES and NO.
Yes, Dave and Plamen are right: digital relay's contacts
are common failure point ( after power supply
Cranky108 , problem is breaking current, in few case possibe connect two contacts in series, but it always good solution.
Yes, from time to time contacts are burned.
But from time to time aux. relay dosen't work or burned, trip coils too. But we don't add second trip coils in the MV.
LOR also burned.
Possible build some module with capacitor and resistor and add it to parallel with trip contact.
I think two ways are solution:
1. if digital relay are "simple" and contact burn, replace relay.
2. If relay are excpensive, always in design leave one or two contacts as spare.
Regards.
Slava
RE: Do we still need tripping relays
I have been looking at two possible solutions.
1. high interrupting contacts on digital relays.
2. have 86BF contact open trip current, with a fuse or other desposible device in parallel.
Tripping relays can still have a few functions, but not with digital relays (Sudden pressure aux.?).
RE: Do we still need tripping relays
Please see attached thread on the issue of "non-electrical" protection.
thread248-209857: Transformer Relay Tripping Question
And again.
i think, today, with newer reley are included communication, BI/O cards, remote modules, we need try use minimum aux. relays.
But, if we use only one digital relay for the trafo/generator/motor protection -- for the "non electrical" protection, we MUST use aux./trip relay.
BTW, LOR today is also standard protection function of newer relay ( also with memory).
Regards.
Slava
RE: Do we still need tripping relays
RE: Do we still need tripping relays
Problem is:
1. this contact is damage.
2. CB not opened.
3. Relay work with some pulse and open faster then 52a contact.
OK, it happend, once in few years. I preffered replace relay and not add aux. relays.
Just my opinion.
Best Regards.
Slava
RE: Do we still need tripping relays
On a feeder, we no longer use them.
RE: Do we still need tripping relays
And Jghrist you are right the 52A breaks the trip coil current most of the time. The problem is when it dosen't.
RE: Do we still need tripping relays
RE: Do we still need tripping relays
If you don't have DC power available then a microprocessor relay probally isen't a good idea.
I would think that a tripping relay would not be advisable, except if this is a transition device where you have both DC and a capacitive triped breaker. In that case a tripping relay is a solution.
RE: Do we still need tripping relays
Lock-out relay is another issue.
I also do not agree with the fact that you need to consider the breaking capacity of output contacts of the relay. Why?
That contact is not breaking anything. It is the normally open contact in series with the trip circuit, inside the circuit breaker, that opens the inductive circuit. The relay resets (in the worst case) when the primary current has been removed, so after that the CB has physically opened.
Eventually you should consider the making capacity of the contact, but the todays contacts are more than enough.
The only case where you "burn" the binary output is in case of breaker failure. In this case, by default, the output card of the relay is replaced, without any check.
RE: Do we still need tripping relays
I just think I may have a solution that solves this.
RE: Do we still need tripping relays
Yes, trip contact not disconnect anything, in case of CB trip coil.
But in newer relay same contacts ( I mean, power type contacts) used for the control too. Close coils of CB, contactors of disconnectors,block magnets, etc. In this case we have check breaking current ( I think so).
BTW, once we worked with VMxx MV CB, nice work, no problem with contacts, no close and trip coils, all CB control is electronic card.
Best Regards.
Slava
RE: Do we still need tripping relays
A tripping relay is one more thing that can fail. The same applies to lockout relays, but at least they serve a different purpose. I have used relay contacts to trip breakers directly in addition to tripping a lockout relay. This increases speed and provides a backup in case the lockout relay fails.
RE: Do we still need tripping relays
I'm a little leary of small UPS's because they tend to be forgotten about.