Primary Protection for Transformer by Fuses

Then look here: International Program IEC - The IEEE Standards Association

If you are working to a standard you should have a copy, and use it.

Someone's life may depend on what you are doing!

Get the standard, or hire a PAID consultant.

Selection of HRC fuse (providing short circuit protection only) or Circuit Breaker (facility to provide various protection and control functions) as primary side protection of Transformers depends mainly on economics and criticality of application. For lower rated transformers, the cost of circuit breaker will be equal or more than the cost of transformer which it protects and hence does make economic sense. Typically transformers rated 1000 KVa and above will be provided with circuit breakers as primary protection as cost of breaker will be some percentage of cost of the transformer it is protecting. Also from 1000 KVA rating, provision of WTI, OTI, Bucholz, surge protection devices etc (mechanical protection devices) becomes mandatory. With these protections in place, you will need tripping mechanisms for isolation of transformer from source, which HRC fuses cannot provide. Breakers for smaller rated transformers are employed in case the transformer is used for some critical application (where transformer cannot be allowed to be shut down and all necessary protection to safe guard the transformer are incorporated in the breaker) and/or based on requirement of operation through remote switching. However these are exceptions rather than normal.

Present day breakers (both primary & secondary side) are provided with solid state (electronic) or numerical based (software driven) protections which are field proven and widely used.

Please note that if you are using breakers, you can build in all kinds of required protection schemes, like overcurrent, short circuit, over/under voltage, earth fault etc, which is not possible with HRC fuses which offer only current based short circuit protection. Also the breakers can be "built intelligent" for remote control, metering etc and this is simply not possible if HRC fuses are provided as incomer control.

Slowly as the cost of breakers are coming down, the requirement of both operation and control of primary and secondary equipment's are going up, the usage of breakers as both primary and secondary protection and control equipments is gaining popularity, irrespective of the capacity of the transformer.