The test transformer is the basic test equipment used for AC withstand voltage test by a large number of users such as power plants, power supply bureaus and scientific research institutions. It is used to conduct dielectric strength tests under specified voltages for various electrical products, electrical components, and insulating materials. The insulation level of the product, the insulation defect of the tested product is found, and the ability to measure the overvoltage.

The voltage regulating switch of the test transformer is a rotatable part of the transformer, and it is easy to cause the machine to heat up due to poor contact and cause failure. For this kind of switch failure that is easy to occur, we must be prepared to deal with this kind of failure. To check and judge the following aspects:

1. Whether there are burn marks (singeing) and poor contact on the fixed and movable contact surface, and whether there is sludge deposit on the contact surface.

2. Whether the transmission mechanism of the pressure regulating switch is flexible. Test whether the pointer on the cover of the transformer is indicated on the position mark due to excessive looseness of the transmission mechanism of the transformer, and the contact is not yet closed at this time. Whether the three-phase contacts of the switch are closed at the same time, and whether the tightness of the spring is the same.

3. Whether the joint between the switch's operating lever and the box cover is tightly connected, and whether the gasket is complete. Check whether there is water stains under the cover hole of the operating lever.

4. If a wiring board type tap is used, check the tightness of the pile heads of the wiring bolts, whether there is sludge accumulation between the wiring pile heads, and ensure that the pile heads are clean and intact, otherwise short circuit or flashover is easy to occur trace.

5. When inspecting the on-load switch of the test transformer, take out the core part of the switch and rotate it back and forth to observe whether its contact limit action is smooth and continuous. At the same time check its transition resistance to determine whether its connection is stable and reliable.