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Distance Element Response to Distorted Waveforms

Distance elements are widely used on transmission, sub-transmission, and even many distribution systems. Distance-based schemes are a very economical and simple approach to protecting lines. The performance of distance elements is based on reliable currents and voltages measured at the relay terminals, typically from current transformers (CTs) and voltage transformers (VTs). Sometimes, the power system or the instrument transformers produce a distorted waveform. These distorted waveforms can be due to CT saturation, capacitor voltage transformer (CVT) transients, or power system events such as faults on series-compensated lines, line switching, or transformer energization.

This article studies the impact of distorted waveforms on distance-based elements, such as mho or quadrilateral elements. The impact to the reach (underreach or overreach) and operating time are evaluated, and possible solutions are discussed. More

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