Main protection of microprocessor based motor is differential protection and quick-break protection.

This paper calculates the result by the project example,expounds the importance of instantaneously over-current protection on the bus fed static excitation system,and analyzes the excellence and defect of several project of phase current instantaneous trip protection on exciting transformer by reliability,quick-action,selectivity and sensitivity of the protection.

Through analysis and calculation of setting principles and sensitivity for instantaneous trip protection of a low-voltage transformer, the differential protection can be cancelled and can use instantaneous trip protection as the main protection of a low-voltage transformer in order to simplify the protection configuration, and reduce the rate of mal-operation.

Analysis of maloperation of generator differential protection caused by transient unbalanced current;

Analysis of mal-operation of transformer differential protection;

Analysis and solution of misoperation of transformer differential protection when external ground fault occurs;

Communication clock setup in the current differential protection based on optic fiber;

Analysis on the transformer differential protection acting in error and the treatment;

Job elements in vertical differential protect of electric transformer and protect bound in course of electric transformer are introduced.

Compensating measure of transient capacitive current of UHV transmission line on differential current protection;

Abatract: Based on the study about the influence of the distributed capacitance current of UHV transmission line on differential current protection,a principle which is free from capacitance current impact is put forward in this paper.

Based on the study about the influence of the distributed capacitance current of UHV transmission line on differential current protection, a novel accurate compensation method of capacitance current is proposed.