UnderVoltage Relay (27) Shall be trip the CB or just alarm only?

[ciy]

Hi,

Please advise when undervoltage Relay (27) Shall be trip the CB or just alarm only?

What is need to concern?

Is there any criteria for following?

Thanks.

ciy

 

[ScottyUK]

Depends on the load.

 

[slavag]

Usually in case of motors or capacitor banks. Used for generators too.
Of course in ATS

 

[DTR2011]

Quite a few "ice cube" undervoltage relays used in SCADA/control applications.

 

[mastergate]

I think undervoltage is more a protection for the power source side (grid/generators).
For consumer side, essential protections are current based. Undervoltage is mainly used for load schedding issues.

 

[unclebob]

Useful to prevent motors running on a single phase. Utility here specifies that the voltage shall be between 540 - 636 V.
So, we set our UV's at 90% with a time delay of 10 sec. to avoid nuisance tripping.

 

[constantlylearning]

We use 27 relays for several applications. They are a permissive relay for certain breaker reclose conditions (Hot Bus / Dead Line). They are also a tripping relay in some instances. This is usually applied on a transmission bus that is connected to non-conventional generation. In these cases, generation is on the low side of a substation transformer, so their is no zero sequence path for ground faults. The only way to detect a transmission ground fault from the perspective of generation is to sense low/no voltage on an individual phase. USUALLY though, this would be accompanied by a zero-sequence over-voltage relay.

But I digress. This is probably not the application you are concerned with.

 

[ciy]

Dear all,

Thanks for your reply.

Is there any guideline for reference?

ciy

 

[davidbeach]

There are no universal answers, every application is different. If it makes sense to trip on undervoltage then trip on undervoltage but if it doesn't make sense to do so then don't. Sometimes "what makes sense" will be clearly spelled out, an interconnection agreement for instance, and sometimes it's up to the protection engineer to figure it out. Where you are plays into it too, what is commonly done in one part of the world makes no sense elsewhere.

 

[krisys]

I fully agree with davidbeach.

Application of under voltage relay shall be driven by the power system and the scope of work.

For the generic question, generic answer !!!

 

[ciy]

Dear davidbeach and krisys,

Thanks your reply.