Lock out Relays

[Electriman]

Dear Friends,

I have two questions about lock out relays.

Most of the digital relays i.e. SEL 751, Multilins and so on they already have the option to lock the faults (lock out relay feature). But I still have seen people consider a separate lock out relay on the switchgear feeders. So my questions are

1-What values does any separate lock out relay add to the design when we know SEL or Multilin have already the lock out feature?

2- My second question is if we decide to put a separate lock out for transformer trip (sudden pressure relay) do you put it on the transformer or down stream switchgear?

 

[iceworm]

... 1-What values does any separate lock out relay add to the design when we know SEL or Multilin have already the lock out feature?

Well, you need a way to reset. Operators like an Igor style switch - the same type that has been is use for the last 100 (maybe 150) years or so, works well.

... 2- My second question is if we decide to put a separate lock out for transformer trip (sudden pressure relay) do you put it on the transformer or down stream switchgear?

If the transformer protective relays indicate a sudden pressure trip, something really bad has happened inside the transformer. This is not about saving the transformer, it likely need rewinding or replacement - it's about getting the fire put out. One wants to remove the power source to the transformer really quickly. The CB to trip is the transformer primary feeder.

ice

 

[Electriman]

... 1-What values does any separate lock out relay add to the design when we know SEL or Multilin have already the lock out feature?

Well, you need a way to reset. Operators like an Igor style switch - the same type that has been is use for the last 100 (maybe 150) years or so, works well.



If the transformer protective relays indicate a sudden pressure trip, something really bad has happened inside the transformer. This is not about saving the transformer, it likely need rewinding or replacement - it's about getting the fire put out. One wants to remove the power source to the transformer really quickly. The CB to trip is the transformer primary feeder.

ice

Thanks. Supposedly, we trip the transformer incoming side, but my question is where do you put the lock out relay? Do you put it on the transformer control box or do you put in the switchgear where the incoming breaker is?

 

[iceworm]

..., but my question is where do you put the lock out relay? Do you put it on the transformer control box or do you put in the switchgear where the incoming breaker is?

I don't know what a transformer control box is.

If by "lockout relay"you mean something like an 86T, normally it is next to the rest of the transformer CB controls/protective relays.

ice

 

[Electriman]

I don't know what a transformer control box is.

If by "lockout relay"you mean something like an 86T, normally it is next to the rest of the transformer CB controls/protective relays.

ice

Yes. That is what I meant 86T. You would put it in switchgear next to rest of protection 87 and 50/51 and CB.

Thanks,

 

[SG-1]

Besides providing a trip signal that has to be manually reset, the lockout relay is usually wired to open the breaker closing circuit. This way the breaker cannot be reclosed into the fault by a remote signal.