Abstract
This paper presents an Intel 8086 microprocessor-based quadrilateral distance relay suitable for the protection of EHV UHV transmission lines. The digital filtering algorithm used for extracting the fundamental frequency components from the complex post-fault relaying signals is based on rationalized Haar transform (RHT). The real and reactive components (R and X) of the apparent impedance of the line as seen by the relay are computed by using the real and imaginary components of the fundamental frequency voltage and current phasors. Using the computed values of R and X, the microprocessor 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 microprocessor issues a trip signal to the circuit breaker. The proposed distance relay is reliable, flexible, accurate and fast.
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