Bucholz Relay

This sounds like a test question....Do your homework kid...

Dear Solar Eagle

Its not a homework, my experience with other project that most transformers we install with rating 3MVA,2MVA,1.5MVA etc. is that we dont use this bucholz relay may be my exposure is mostly ansi standards, now the current project uses IEC standards where 2MVA,1.5MVA has oil conservator and bucholz relay, I think that is the difference with the 2 standards.

A Buchholz relay can be used on any oil-filled transformer with a conservator. When the design was created 90 years ago, your 1.6 MVA unit was a significant size for a transformer. Manufacturing techniques and factory testing were not yet standardized, and the cost of a replacement transformer was a large percentage of a capital budget.

The question to answer is whether the cost of the relay (including maintenance and testing) is worth the cost of not having it. We typically don't use a conservator on any transformers, opting instead for a larger tank with nitrogen-filled gas head space above the windings. Without the conservator, Buchholz is not an option. Instead, we use differential protection on substation and generating station transformers, which is faster and more reliable than a Buchholz relay.

But according to ansi standards differential protection is applicable for xformers 5MVA and above how about for padmounted xformers mostly located indoors ranging size is from 1,1.5,2 and 3MVA does the need for conservator and bucholz relay is necessary?

The buchholz relay is very simple and cheap which operates when there is an internal fault in the transformer leading to sudden in-rush of oil to the conservator.

It is always advisable to go for this relay for such oil filled transformers in order to minimize the damage.

Even if differential protection is provided for the transformer,this will act as a back up protection for the internal faults.

Vide Indian Electricity Rule 64A (2) (c):

"Gas pressure type and winding and oil temperature protection to give alarm and tripping

shall be provided on all transformers of ratings 1000 KVA and above".

But, as a general practice, any transformer of rating 500kVA and above is provided with a Buch-holz relay.