Electronic Trip Unit or Relay

[undervoltage]

I have carried out the Relay Coordination for 13.8kV and 380V Electrical System. The Study has been submitted to the consultant. The Low Voltage Circuit Breaker are equipped with Electronic Trip Units. I did the Overcurrent coordination using my protective relays as we are not considering to use LV Circuit Breakers for Overcurrent coordination. The consultant is insisting to use Breaker for Overcurrent coordination.
Is there any standard, which let us know, which device to be used for Overcurrent coordination, in case where we have both ETU (Electronic Trip Unit) equipped LV Circuit Breaker and a Protective Relay.

 

[ScottyUK]

Use the fastest upsteam and slowest downstream realys. I really question the use of two separate relays providing the same function. This isn't normally done except in a duplicate A/B system, and cost normally confines them to protection of transmission and generation plant, not distribution level. Work out what you are going to use, and then calculate appropriately.

Check whether the ACB manufacturer has any qualification on the protective device used with the breaker to achieve nameplate rating. I think ABB have something in the small print for the E-Max range, and if they do then the chances are Siemens and Schneider will for their products too.


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If we learn from our mistakes I'm getting a great education!

 

[undervoltage]

Scotty I dont have duplicate relays on any feeder, I have a Multifunction Digital relay and an Electric Trip Unit on my ACB. Which one I shall use for Overccurrent Coordination, Electronic Trip Unit or Multifunction relay? Any reference to the standards?

 

[rbulsara]

It is more a question of choosing a better design, than any standard. Standards or codes may specify minimum requirement but not quality of equipment.

The LV trip unit in this case would be redundant. Since relays are more accurate and flexible (adjustable) than the breaker trip unit, I would make the relay primary protection and the breaker trip unit a back up (set it as high as possible).

If the relay was not to be used as primary protection, why even have such an expensive device on it? Even if it were for other functions, I would use( and I have used ) relay as the primary protection.



Rafiq Bulsara

http://www.srengineersct.com