Transformer Protection

NOPE. All Transformer have their standard type of protection provided by the transformer manufacture.

For 600 volt and below the primary over current device is 125% of the FLA. This can be changed under certain provisions. Your local code made dictate your choices.

Dear,

Please Go through IS 2026 if you are working for indian project otherwise go IEC60076 section 1 to 11 .

Regards,

Vikas

What I mean is the relay protection. For example, it's not common to provide differential protection for 1250 kVA transformer.

Every country has it own electrical standard code to follows. Down here, small transformer like 11KV/433V from the lowest KVA till 8500KVA, we does not need to install the differential protection for transformer. We just install SPAJ and Earth Faults relay and these both relay is sufficient to protect your transformer.

Only our 35MVA transformer and the 120 MVA transformer, we do install the differential protection including the Overcurrent Protection and Earth faults Relay.

Protection is always require for any equipment. But what all protections to be provided for specific equipments depends on many things like criticality of equipment, application of equipment, probability of re-occurring faults & of course cost involved in the protection.

There is a thumb rule for any protection system. Cost of protection the system should be less then 10% of the equipment to be protected. But normally as you go on bigger equipments this % ratio will come down & for smaller equipments % ratio will be more. Now because of numerical relays this ratio is again going on higher side but it has its own advantages so this is techo - commercial matter.

I have put numerical relays like &SJ61 for motors rating up to 55 kW, due to the criticality of the equipment. In this case %ratio is too high. But over all cost of electrical system & protection cost is again within 10%.

It is preferred that above 5000KVA you should have complete protection of transformer i.e Differential protection,Bucholze Protection.Pressure relaease device & High Winding temperature protection If your transformer is equipped with on load tap changer then its protection. Below this rating you can run transformer with basic protection i.e Over current protection either through switchgear or by providing blow out fuses this is a basic criteria looking to the cost of transformer its protection cost increses.

Anurag

Thank you. That's exactly what I need to know.