Reducing Fault Through Level on Transformer primary

[tctctraining]

Beside using a current limiting fuse in series with standard E type fuse( K type can't be used) on primary side of a transformer ( 10MVA, 28KV), is there any other solution to limit the fault through current?

Thanks

 

[rbulsara]

Series reactors.

Although I am curious as to why do you need to limit the fault current on the primary side? It will have very little effect, if any on the secondary side.

Rafiq Bulsara

http://www.srengineersct.com

 

[tctctraining]

To minimize transformer damage incase of any fault on the secondary side. I've attached the curve with a CL fuse that clears the inrush current too.

 

[dpc]

So which side of the transformer is the primary?





David Castor

http://www.cvoes.com

 

[rbulsara]

tctc:
I think you need to work closely with your senior engineers and use their guidance.

Rafiq Bulsara

http://www.srengineersct.com

 

[tctctraining]

The 27.6 kV side is the primary and 13.8 kV is the secondary. Both fuses the 250E and Cl fuse are installed on the primary side. My understanding is that since 250E fuse protects the transformer damage curve , so there isn't a need to limit the through fault current incase of any fault on the secondary side,since it will be cleared fast enough. in other words , transformer is protected by the fuse and there is no concern about through fault currents.

 

[VTer]

At that transformer size, you should probably look at using CBs and relays for transformer protection in the first place.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[tctctraining]

Primary voltage is 27.6 and there are breakers on the secondary side. Is there a reference to when ( from what MVA rating ) and what type of protection must be used on transformers?

 

[jghrist]

Your diagram shows fuses on the wye side of the transformer. Normally, the 27.6 kV primary would be delta and the 13.8 kV secondary would be grounded wye. That's probably causing some confusion in the posts.

As you can see from the diagram and as you have noted, a through fault is cleared by the 250E fuse and the CL fuse doesn't get into the current limiting range anyway, so there is no limiting of the through fault.

That doesn't mean that you never need a CL fuse on the primary of a transformer. Often CL fuses are used on distribution transformers to limit the energy in a high side transformer fault to prevent catastrophic failure.

This isn't normally done on power transformers. As noted by VTer, this size transformer usually has a primary breaker and differential protection because it acts faster than fuses and can limit damage from a fault. Smaller transformers are cheaper and often do not justify the cost of a breaker.