Microcontroller-Based Numerical Quadrilateral Relay for the Transmission Line Protection

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Abstract
This article presents an Intel 8097 microcontroller-based numerical quadrilateral distance relay for transmission line protection. The numerical filtering algorithm used for the extraction of fundamental frequency components from the corrupted post fault relaying signals is based on Block pulse functions. The microcontroller computes the real and reactive components (R and X) of the apparent impedance of the line as seen by the relay by using the real and imaginary components of the fundamental frequency voltage and current phasors. Using the computed values of R and X, the microcontroller examines whether the fault point lies within the quadrilateral relay's protective zone or not. If the fault point lies in the protective zone of the relay, the microcontroller issues a trip signal to the circuit breaker. The relay is successfully tested for a number of different three step quadrilateral characteristics and the results are obtained. The proposed relay is reliable, flexible, accurate and fast.

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