ahmed soliman


{ City } cairo
< Country > egypt
* Profession * electrical
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Question { Qatar Gas, 3545 }

Why Diffrential and Ref relays are used together although
Diffrential relay can protect Pri and Sec of Transformer


Answer

The normal bias setting in a differential relay is 20%.
So, complete earth fault protection is not possible with
differential relay. That is why you need a seperate earth
fault relay with sensitive settings like 5%.

Is This Answer Correct ?    1 Yes 0 No