Analysis of induced voltage in metal shield of power cable and research on its restraining technology based on asymmetric state

Three segments transposition is often used to decrease the induced voltage in metal shield of high voltage power cable, But since the power cable is rebuilt more and more frequently caused by city construction, the length of the three segments will be unequal while the power cable rebuilt, which will make the induced voltage in metal shield unbalanced, and produce the circulating current in metal shield. On one hand, the induced current will lead to energy loss and the falling of transmission efficiency, on the other hand, it will cause the cable temperature to rise, influence the cable life, and decrease the transmission capacity. Based on the theoretical analysis, mathematic models of the induced voltage in metal shield under several main arrangement ways of power cable were deduced in this paper. The compensating method of induced voltage in metal shield of power cable was put forward. Based on these methods, the computing software package of compensating unit was developed, computing emulation was taken. Based on it, the compensating unit was developed. By changing air gap and turn number of the compensating unit, it can compensate the induced voltage effectively, and reduce the synthesis induced voltage in the metal shield greatly, reduce the circulating current in the metal shield efficiently, then decrease the loss of power cable and increase the transmission capacity greatly.