Differential Pilot Wire Protection is simply a differential protection scheme applied to feeders. Several differential schemes are applied for protection of line but Mess Price Voltage balance system and Translay Scheme are most popularly used.
Bus Type - Known Parameter - Unknown Parameter Load Bus -P, Q - V, phase angle Generator Bus - P, V (magnitude) - Q, Voltage phase angle Slack Bus Voltage - magnitude and phase angle - P, Q
Buchholz relay is used for protecting transformer against incipient or internal faults. Buchholz relay is a gas-actuated relay installed in oil immersed transformers for protection against all kinds of faults.