| Summary: | The paper explained that traditional leakage protection principles such as zero-sequence direction relay principle and zero-sequence current's maximum principle are unable to implement selective leakage protection in situation of great disparity between long and short lines and big unbalanced current through analyzing an actual example, and proposed a scheme of selective leakage protection in the situation by use of zero-sequence current's break variable principle. The scheme judges leakage by comparing zero-sequence current with inherent capacitive current of each power line as follows: if zero-sequence current of one power line changes suddenly compared to inherent capacitive current, then the power line would be leakage line; if zero-sequence current of non power line changes suddenly compared to inherent capacitive currents, then main line leakage happens. The application showed the validity of the zero-sequence current's break variable principle.
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