Do we still need tripping relays 2

[SMB1]

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,,

 

[slavag]

Hi.
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

 

[cranky108]

NO.

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?

 

[dpc]

External lockout relays are still widely used for a variety of reasons including contact rating, quantity of contacts, visible indication, physical presence required for reset, etc.

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.

 

[oldfieldguy]

I use numerical relays exclusively for protection, but I route some functions through a separate electromechanical 86 lockout relay because nothing says serious electrical fault to my people like the orange flag and turned handle of that old-fashioned relay, as "dpc" says.

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

 

[lz5pl]

Almost every relay protection manufacturer declares at least several "trip" contacts of it's relay protection with big current capacity (physically smaller than those old relays, but...) and theoretically external auxiliary trip relays are not necessary.
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.

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[slavag]

Hi.
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

 

[cranky108]

It not just digital relays with the problem of welding, it is also possible on lockouts, as they are also not rated to break tripping current.
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.?).

 

[slavag]

Hi Cranky.
Please see attached thread on the issue of "non-electrical" protection.
thread248-209857
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

 

[jghrist]

Why the concern with breaking tripping current. There is always a 52a contact in series with the breaker trip coil that breaks the tripping current.

 

[slavag]

Yes, Jghrist, exectly!!!
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

 

[DiscoP]

We only use tripping relays for locking out on Busbar or Transformer protection.

On a feeder, we no longer use them.

 

[cranky108]

I perfer a lockout to a tripping relay for differential protection.
And Jghrist you are right the 52A breaks the trip coil current most of the time. The problem is when it dosen't.

 

[jghrist]

What if tripping is with a capacitive trip device (no dc available for tripping)? I have been told by one manufacturer that their microprocessor relay contacts can be damaged by the surge that is put on the system by the capacitive trip device. In this instance, I used tripping relays to isolate the microprocessor contacts from the capacitive trip device. I have been told by other manufacturer that this is not a problem with their relays.

 

[cranky108]

If you are using a capacitive trip device, what are you using for tripping and control power?

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.

 

[521AB]

To my opinion and experience, the trip umit is not needed. There are anyway a lot of specifications where it is requested direct connection between relays and Circuit Breaker coils, no aux. relay in between.
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.

 

[cranky108]

As I said above "most companys I asked a few years ago said welded contacts and burned up trip coil is part of a failed breaker."

I just think I may have a solution that solves this.

 

[slavag]

again yes and no situation.
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

 

[jghrist]

If you are using a capacitive trip device, what are you using for tripping and control power?

If you don't have DC power available then a microprocessor relay probally isen't a good idea.

AC tripping and small UPS for relay power (not big enough for tripping with dc).

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.

 

[cranky108]

Have you consitered using two relay contacts in series. You would have to remove the MOV's on the contacts, and there is an article on one of the relay manufactures web site.

I'm a little leary of small UPS's because they tend to be forgotten about.