Differential Transformer Protection

As I recall, some power transformers have very high values of magnetizing inrush current when the breaker is closed. Those currents can be high enough in magnitude and duration to cause relay operation. To prevent that, some form of auxiliary magnetizing inrush tripping suppression is necessary. However, in many cases, induction type differential relays are used on transformer banks having high magnetizing inrush current (by increasing the contact travel, increasing the relay damping, or both) to eliminate the need for auxiliary devices to block nuisance tripping.

Bank transformers, say, a set of three single phase transformers adequately connected, may be easely protected with several multi functions protective relays.

The functions you will need will depend on system requirements, as well as the connection of the bank.

These protections are all included in a single relay and includes, at least the following functions:

-differential protection

-restricted earth fault protection

-high voltage phase and neutral overcurrent protection

In some cases, you may have negative sequence protection as well

For further information, please refer to specialized manufacturers.

I suggest SCHWEITZER, which has a very rich technical site: www.selinc.com

This is only one of the manufacturers, but the advantage is that they will provide you full assistance, as welll as, if you purchase the equipment, you own a 10 years warranty period, free of charge.

Further to SCHWEITZER, you may contact GE or ABB.