Abstract. Voltage transformer may appear disconnection fault at operation time. This will greatly affect the protection devices work properly. Thus the impact of this failure, as well as an accurate method of determining the fault is worth studied. In this paper, based on the actual grid model, the specific effects caused by the fault were analyzed principally. And whether the general methods could identify the fault in several conditions is simulated.

Abstract. In this paper, based on finite element method, Ansoft was adopted to study the static and dynamic characteristics of electromagnetic release. Firstly, electromagnetic release was split and made models. According to the actual material properties, the corresponding parameters were set. And after creating the mesh, calculation was processed. The results show how the electromagnetic force changes with the current and the performance of electromagnetic release in different short circuit current. OverviewElectromagnetic release of miniature circuit breaker is the core component of over current protection. It must meet the requirements of the tripping characteristic curve when the current is less than the specified value must not trip when the current value exceeds several times the rated current is required in accordance with the inverse-time tripping characteristic curve [1] . Due to the shorter trip time, the faster the circuit breaker cut short circuit. Therefore, the performance of electromagnetic release a greater impact on limiting miniature circuit breakers and breaking properties, Electromagnetic release of dynamic and static characteristics are very necessary [2] . This paper used Ansoft to calculate the electromagnetic force solenoid type electromagnetic release, and static and dynamic properties of electromagnetic release were analyzed.