DC offset currents are a transient phenomenon that occurs when a transformer is energized. These currents are a result of the core saturation during the initial energization. The magnitude and duration of the DC offset depend on the voltage at the instant of switching and the residual flux in the core. These DC offset currents significantly impact protective relay performance. Differential relays, which protect transformers by comparing the currents entering and leaving the transformer, can be particularly affected. The DC offset can cause the CTs (current transformers) to saturate, producing distorted secondary currents that the differentia....
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