Minimum Rating of Transformer for Which VCB is Required

Requirement of VCB for transformer not only depends upon its KVA rating but also on the financial investment of your company,importance of the transformer,reliability of the system etc.

So it depends on you

IE Rule 50. Supply and use of energy-

(1)The energy shall not be supplied, transformed, converted or used or continued to be supplied, transformed, converted or used unless provisions as set out below are observed:

(a)The following controls of requisite capacity to carry and break the current are placed after the point of commencement of supply as defined in rule 58 so as to be readily accessible and capable of being easily operated to completely isolate the supply to the installation, such equipment being in addition to any equipment installed for controlling individual circuits or

apparatus:-

(i) a linked switch with fuse(s) or a circuit breaker by low and medium voltage consumers.

(ii) a linked switch with fuse(s) or a circuit breaker by HV consumers having aggregate installed transformer/apparatus capacity up to 1000 KVA to be supplied at voltage up to 11KV and 2500 KVA at higher voltages(above 11 KV and not exceeding 33KV).

iii) a circuit breaker by HV consumers having an aggregate installed transformer/apparatus capacity above 1000 KVA and supplied at 11 KV and above 2500 KVA supplied at higher voltages (above 11 KV and not exceeding 33KV)

(iv) a circuit breaker by EHV consumer: Provided that where the point of commencement of supply and

the consumer apparatus are near each other, one linked switch with fuse(s) or circuit breaker near

the point of commencement of supply as required by this clause shall be considered sufficient for the

purpose of this Rule.

(b) In case of every transformer the following shall be provided:-

(i) On primary side for transformers a linked switch with fuse(s) or circuit breaker of adequate capacity.

Provided that the linked switch on the primary side of the transformer may be of such capacity as to carry the full load current and to break only the magnetising current of the transformer.

Provided further that for all transformers:-

(A) having a capacity 5000 KVA and above and installed before the commencement of the Indian Electricity (Amendment – 1) Rules, 2000 and

(B) having a capacity of 1000 KVA and above and installed before the commencement of the Indian Electricity (Amendment – 1) Rules, 2000; a circuit breaker shall be provided.

Provided further that the provision of linked switch on the primary side of the transformer shall not apply to the unit auxiliary transformer of the generator.

(ii) In respect of all transformers installed on or after the commencement of the Indian Electricity (Amendment-1) Rules, 2000, on the secondary side of all transformers transforming HV to EHV, MV or LV;

a circuit breaker of adequate rating shall be installed:

Provided that for suppliers' transformers of capacity up to 630 KVA, a linked switch with fuse or circuit breaker of adequate rating shall be installed on secondary side.

Circuit breaker required is compulsary a VCB or it may be ACB or OCB of adequate capacity.