Our modern life depends on electric power very much and, this electric power is to be sent by power cable. In order to send the power in stable condition, the reliability of the cable is extremely important. However, for the cables are being used at sea and underground, the degradation phenomena of the cable can be found. Water tree is one of the main degradation of the cables. There are several methods to investigate the degradation of cables. Among them we are using simulation method to detect water tree by using loss current method.

　ケーブルの劣化現象の一つである水トリーは，加える電圧値や周波数によりその形状や進展速度は異なります。私たちは水トリー劣化試料を回転対象等価回路モデルに置き換え，回路シミュレータ（LTspice）を用いることで，水トリー周辺の電界値を計算し，これから水トリーがどのような形状で進展していくのか予想しています。これにより，どのような電圧，周波数がより水トリー劣化の危険性があるのか，予測できます。

※三菱電線工業時報第105号より

 Since the AC voltage is applied to the cable, the electric field value in the vicinity of water tree will continue to change over time. It is difficult to measure the electric field experimentally which will change in a short period of time. In order to calculate the electric field values of the water trees and to visualize the electric field in the vicinity of the change to water trees, simulation works are carried out by using a circuit simulator (LTspice). Our works can be helpful to understand the phenomena of water tree in the cables.