Based on the present domestic electric power market two quite mature algorithms(accountant cost law and marginal cost law),the transmission and distribution electricity price does not involve the problem of unbalanced power supply compensation and make the quantification analysis.

The paper introduces the principle of cells transverse differential protection,and makes analysis on the reason of large unbalance current of Longyangxia hydropower plant cells transverse protection,as well as proposes solving methods and its importance.

According to the test results the HV capacitor banks which the unbalance current is larger have been adjusted.

Analysis of the voltage unbalance in the small current grounding system;

When a submarine cable of 35kV is energized, the voltage unbalance between lines and grounding alarm are arisen.

Furthermore, a novel control strategy was proposed to mitigate voltage unbalance and at the same time extend the functions of SVG.

New energy-saving equipments for adjusting unbalanced currents and compensating power factor;

Based on the loop equations of transformer model, utilizing the unbalanced current in the delta windings to establish the relations among the three-phase loop equations, a winding unbalanced parameter loop equation under the normal operation is obtained.

When there is no fault within protection range,unbalanced current inside differential relay is near to zero;but on some cases,there does still big unbalanced current exist.