Abstract:This paper introduces the effects of current transformer in power system, analyze the causes why current transformer secondary circuit can’t open and the possible consequences when it opens. Several cases of incorrect wiring of the secondary circuit of a current transformer are enumerated, and the harm of different error connection modes are analyzed, It is further proved that the correctness of the two circuit of current transformer plays an important role in ensuring normal operation and power grid safety of relay protection, safety automatic devices and measuring devices. And it leads to the two methods of the secondary circuit check of current transformer: the disconnect checking method and short circuit checking method. The implementation process and principles of the two checking methods are mainly analyzed, From the two aspects of work efficiency and operational risk, two checking methods are compared and analyzed, It is concluded that the disconnect checking method has the shortcomings of low work efficiency and high operational risk, while the shortcut checking method has the advantages of high work efficiency and low operational risk. Obviously, compared with the two, the short circuit checking method is better than the disconnect checking method, and it is worth popularizing and applying in all power system.