Circuit Breaker

In our plant we use OCB for 5MVA 11KV/250V TFR.

i would suggest that have you oil CB to be tested first before making decision on buying new one..

if the CB test fails according to your standards used, then you could a new one.

in choosing what to buy, i would against suggest to make what you need, i mean, what CB do you what.. then make a technical data sheet and have it filed by the manufacturer that you prospected to buy.

if you are talking about the interrupting medium as your best criteria in choosing a CB, i would suggest that would follow according to your environmental standards.. for this voltage level, 11kV, i would suggest a vacuum circuit breaker with solid dielectric for it has no environmental issues regarding in interrupting medium..

hope that it helps.. and also consider the first cost in buying and the operating cost of the CB..

i think Vacuum CB is now very much used at this voltage, if you mean the 11kV side.

MCB is the best for you. you can continue with oil circuit breaker. change the oil to sunflower oil or olive oil.

Any High Voltage Circuit Breaker (viz.) a Bulk Oil CB or a Minimum Oil CB or a Vacuum CB or an SF6 CB would serve the purpose. You have to analyse the pros and cons of each CB in your application with respect to Capital Cost, Running Cost, Maintenance Needs, etc.

However, the present norm is to go for VCBs for such applications.