[manishsarkar]

I want a little help in selecting a VCB for a 33 KV line, with three 1.5MVA transformers and the total load distributed in the LT side is about 4 kilo-watt?
I want to design a panel in the HT side with appropriate VCB ratings feeding 33kv line to the three 1.5MVA Transformer.

[manishsarkar]

Sorry, the distributed load is 4mega watt not 4 kilo-watt.

[Newton1Law]

You total Load is 4 Megawatts and you have a total trnsformation of 4.5 MVA. Based on the transformer capacity of 1.5 MVA at 150% or 2.25 MVA, the priamry current to each transformer is only about 40 amps. Any three phase VCB that you might buy that is rated at 33 kV will most certainly be large enough for the current load. They will most likely be 600, 1200, 2000 amp rated vacuum breakers. The next item you need to address it the fault duty they will be required to interrupt. If the fault duty on the load side of the VCB is say 10,000 amps, the VCBs will have to be rated to withstand 10kA, taking in to account the asymmetrical fault you may want to increase the rating to 20kA. VCBs are readly available for this application.

Last, the type of relaying required would need to be reviewed. Will yo be using transformer differential realying to protect the transformers? What about harmonic restraint relays for when you energize the transformers under no-load conditions? Also, how are you protecting the transformers for an internal high impedance fault? Pressure differential or sudden pressure relays?

A place to start might be:

http://www.abb.com/product/db0003db002618/b648efb374db3fa0c125754e0046c50b.aspx?productLangu age=us&country=US

Hope this helps,

Newton1Law