The long-term unbalance of the three-phase direct-current electric resistance of the coal mine substation host transformer,has led to grave product of tap changer charcoal,insulation oil flash point reduces,threatens the safe operation.

For instance,the effectiveness of fire-extinguishing device,whether or not necessary to install the tap changer and how to determine the economic ratio of losses between no load and on load.

The paper presents configuration and operating principle for noncontact tapping switch that can on-load regulate voltage automatically.

The main idea of measuring the capacitance between line and earth using the tapping switch, which can be used to help to find the grounding failure line, is also di.

The paper discussed the reason of tap changing switch fault,introduced the structural characteristics of this kind of rectification transformer.

The paper analyzes main problems of the mechanical tap changing switch of a transformer in practical use,presents the mechanical tap changing switch how to reform improvement and design of electrical control and relevant electrical circuit diagram.

IEC Standard Evolution and Tap-Changer Technology Development;

To guarantee parallel distribution transformers working safely and prevent tap-changers from different grades,theoretical calculation of the circulation current and the abnormal current due to different grades of tap-changers is conducted,and fault analysis is performed.