According to the load graph of motor under variable load, this paper introduces some ways to select motor power through calculating the equivalent electric current when the calorific capacities of motor at each short-term interval are equal.

On the basis of equivalent current method, this paper deduces the fomulas for calculating starting torque and quality factor of capacitor start single phase motors in which the main winding and the auxiliary winding are displaced by any space angle.

According to a special cross-country fault occurs on certain 220 kV transmission lines,this paper calculates the fault components of current and voltage and analyzes the performance of line protection based on the method of equivalent current and sequence component.

Based on the equivalent current method,the operation performance of the motor is studied and the symmetrical operation condition is set up.

Under the condition of considering the influence of the fractures,the equivalent thermal conductivity coefficient matrix is derived according to the equivalence of heat flux in multi-fractured rock masses.