Studies of distance protection with a microprocessor for short transmission lines

A type of zero-sequence reactance relay suited to short transmission lines with a microprocessor is introduced. It has a greater fault tolerance and is less sensitive to load current. A new derivative-Fourier filter has been developed that can eliminate the influence of higher harmonics and restrain the damped DC component in the power system. Based on analysis and calculation, a fault detection scheme that operates correctly when a power swing follows a fault is presented. Power-swing blocking and fault-phase selection are discussed, and a complete, microprocessor-based protection system is discussed