Could someone tell me the difference between biased and unbiased differential protection? If there is link of unbiased differential protection question and solution, that would be helpful.

Unbiased differential protection set ups have a disadvantage of being too fast and sensitive. As a result, they may even operate on slight overloads or momentary faults.

To prevent such unwanted operation, biased differential is used. Another winding is provided in the relay which tries to hold back the relay.

This coil is called the Restraining Coil. It normally has 20-30% of the number of turns in the main Operating Coil.

There are advantanges and disadvantages in both biased and unbiased impedance protection, now a days mostly biased diffrential principle is used, for a substaion having multiple bus configuration biased is the best suited one, we can use different ratio CT and effection of CT saturation can be easily overcome