protection drawings standards
protection drawings standards
(OP)
hi
i want to find out if there is a specific standard when it comes to duplicate protection. when wiring two differnet protection relays for a transmission bay, should the tripping circuit for the trip coils be seperated. i know that in my experience when we have 2 distance relays they are powered up by individaul dc supplies and their tripping contacts are used to trip both trip coils. now here where i am working it is a standard to keep thier protection completly seperate ie one relay only trips one trip coil. i need to find out whether this is a standard or a preference. it will come down to relaibilty versus standards.
thanks people.
i want to find out if there is a specific standard when it comes to duplicate protection. when wiring two differnet protection relays for a transmission bay, should the tripping circuit for the trip coils be seperated. i know that in my experience when we have 2 distance relays they are powered up by individaul dc supplies and their tripping contacts are used to trip both trip coils. now here where i am working it is a standard to keep thier protection completly seperate ie one relay only trips one trip coil. i need to find out whether this is a standard or a preference. it will come down to relaibilty versus standards.
thanks people.






RE: protection drawings standards
I know on transmission-systems they use duplicate protection due to the high cost of the equipment. I think it was in the beginning just for reliablity, but I'm almost sure it would be incorporated now into a standard. Sorry I have no references.
Regards
Ralph
RE: protection drawings standards
Might be something in the IEEE paper on trip circuit design:
http://www.pes-psrc.org/k/rlytrckt.zip
RE: protection drawings standards
RE: protection drawings standards
this is for 400kv ac transmission so reliabilty is very imp. just for clarity:--
i have 2 different dc supplies,which powers up two different relays and the relays each have tripping contacts (one from each relay) tripping the CB. the CB has 2 trip coils and each coil gets energised by the tripping contact of the relays(positive gets switched via the contact) is this ok to keep the tripping seperate. wouldnt it be more reliable if i had two different tripping contacts(1 from each relay) tripping both trip coils? in other words i will have
a trip contact from relay 1
a trip contact from relay 2 both tripping one CB coil Y1
and then the same for coil Y2.
rather than having only relay contact 1 tripping Y1.
thanks for the input so far.really appreciate everyones ideas.
RE: protection drawings standards
He does have a separate coil, he's just not using it in manner that provides much redundancy.
Powercam,
Separate them for the reasons given above. The key to effective redundancy is to eliminate the common failure points. Many modern relays provide multiple programmable outputs, just a matter of programming a second output to trip.
RE: protection drawings standards
One relay tripping both trip coils
Second relay tripping both trip coils
However, if one coil burns out (shorts) then this will render both trip coils useless unless the fusing for the coils is placed in the proper position so that both DC breakers powering these seperate relays do not trip if one coil shorts. Then you have to ask, what if the wire shorts for some reason before the fusing, well then both DC breakers trip rendering it useless.
I could see arguments for seperate trip coils and relays: one relay only operating one trip coil
second relay only operating a second trip coil
Redundancy has opportunities for one to be 'anal' (I am not saying your being anal) if this is a good word, what if your single set of CTs feeding these two relays fail? Your redundancy is rendered useless. Chances are, as well, that both DC supplies originate from the same source sooner or later (IE the plant goes dark and now your operating on one UPS system (or battery bank) so both supplies are from the same source).
Anyway, enough from me, I think your on the right track.
RE: protection drawings standards
You can hit both tripcoils from one relay by wiring a N.O. tripcontact from the one relay into the other scheme(schemes electrically seperated from each other) and vice versa.
Ralph
RE: protection drawings standards
I know some use relays from different manufacturers. Some will use the same manufacturer as long as different models or algorithms are used. Dual DC systems, instrument transformers, and trip coils still makes little sense to me if you're still relying on the same breaker mechanics. I've seen more problems with the breakers than any other single item.
RE: protection drawings standards
It is definetely the best book written on switchgear, however none of the standards match the ones in North America.
RE: protection drawings standards
An important consideration in the use of dual trip coils is the possibility of a magnetic flux path common to the two coils. Some designs are such that if the two coils are energized simultaneously, but with voltages of opposite polarity, the action of the trip mechanism is defeated. Appendix A www.pjm.com/services/trans/downloads/RS_stn.doc