Relay Trip Contact Rating

[WiringBoy]

Hi
I have a ABB R-Mag 27 kV Outdoor breaker. Relay is SEL 451. I have been told by ABB that tripping current for the breaker ED2 motherboard is 20 mili Amps.

Relay is 120 ft away from the breaker wired through a 125 VDC 10C #10 AWG conductor.

I am using standard output contacts, which the SEL manual qualifies as the following:

"The Standard control outputs are “dry” Form A contacts rated for tripping duty. Ratings for Standard outputs are 30 A make, 6 A continuous, and 0.5 A or less break (depending on circuit voltage). Standard contact outputs have a maximum voltage rating of 250 Vac/330 Vdc. Maximum break time is 6 ms (milliseconds) with a resistive load. The maximum pickup time for the Standard control outputs is 6 ms. "

I am just curious rather I would say in a dlimena, Should I just use these Standard contacts described above with breaking capacity of .5 Amps or I should use High Interupting contacts which has a breaking current capacity of 10 Amps.

I was just shying away from using High interupting contacts due to electronics associated with this contact which has a leakage current of approx. 10 micro amps.

Now Standards contacts have been wired, Do you think that I need to go back and rewire with High interupting contacts or standard contacts is ok.

Just a quick note, In this schematics, because of low trip amperage, 52A is not wired in series with virtual trip coil.
I would appreciate your input.

 

[WiringBoy]

An Addition to my post, Breaking current for Standard Relay Contacts for 125 V DC is .3 Amps. .5 Amps is for 48 V DC.

 

[DTR2011]

I've seen many R-Mag Breakers Wired to SEL Relays with the standard contacts. You are below the 0.5 amp limit.

If you are considering re wiring, use a 52A if a cause for concern. This is a very standard practice.

Is your concern that you are 0.2 amps higher than the breaking current? Consider the margin on a percentage basis.

 

[WiringBoy]

Appreciate your input.
I think I am just being paranoid.

ABB has told me tripping current is 20 milliAmps. SEL standard output contact for 125 VDC is rated for breaking current of .3 Amps. There is not 52A in series.

Where I can go wrong that is what I am trying to find out.

 

[dpc]

I would not be concerned. You could add TDDO timer on the trip output contacts with a short time delay to reduce the risk of the SEL-451 contact opening prior to breaker operation being completed. Unless you are doing high-speed reclosing.

On the other hand, I have use the high output trip contacts on an SEL-351 relay on a R-MAG breaker with no issues (at least that I've heard about!).

 

[WiringBoy]

Thanks DPC. I made my decision.
I spoke to guys in the station they are working after hours and asked them to wire High Interuting contact in series with 52A and the KM1004(virtual trip coil).

Just curious, I have 120 ft of conrol wire 10C,#10AWG at 125 V DC between relay and breaker. Cable capactiance should not be a problem, because there is an IGBT in parallel with the High Interupting contact ?

Any suggestion ?

 

[RRaghunath]

120ft distance I think should not be an issue. 120ft and even more is very commonly encountered in HV Substations.