How do you perform a withstand voltage test using a test transformer?

发布时间：2022-05-11

The test transformer is constructed by stacking cold‑rolled grain‑oriented silicon steel laminations, with steel clamps used for secure fastening. The high‑voltage winding is a cylindrical, multi‑layer, tower‑type design, wound with polyester‑enameled wire and high‑voltage‑rated insulating materials. The low‑voltage winding is positioned on the outside, while the instrument winding is implemented as an independent winding. The enclosure is octagonal in shape, and test transformers rated at 10 kVA and above are equipped with movable iron wheels. These units feature light weight, compact dimensions, easy portability, and superior performance. For the withstand voltage test, the procedure involves connecting the test leads of the equipment to the designated test points—namely, the transformer windings, shielding, core, frame, and other components that are electrically isolated from one another.

Verify that the test equipment can be set to the required voltage range and that its configured leakage current threshold meets the specified requirements. Short‑circuit the high‑voltage output of the test equipment, energize it, and check whether the overcurrent relay operates or whether a breakdown signal is emitted. Inspect the test environment for any potential safety hazards. If none are present, power on the withstand voltage tester and allow it to warm up for 5 minutes. Then, proceed with the voltage‑ramping procedure: at the initial stage, increase the voltage gradually to half of the rated value to avoid overshoot, and subsequently raise it rapidly to the specified test voltage (the entire ramp-up should take approximately 10 seconds), maintaining this voltage for 1 minute. During this period, continuous arcing or flashover must not occur. Finally, slowly reduce the voltage back to zero, disconnect the power supply, and conclude the test.

If the insulation resistance does not change significantly, or if, after a secondary voltage boost, no breakdown occurs for a sustained 1 minute, the breakdown is considered to be an air‑gap discharge—commonly referred to as arcing. Once the applied voltage is removed, the breakdown gap immediately self‑heals, the transformer’s insulation resistance remains unchanged, and its insulation performance is unaffected; therefore, it cannot be classified as non‑conforming. When measuring insulation resistance with a megohmmeter, a reading of zero or near‑zero indicates breakdown. Alternatively, conduct a secondary voltage‑boost test, gradually increasing the voltage: if breakdown occurs, at a certain voltage level you may observe continuous spark discharges or heating and smoking near the breakdown point, which also confirms breakdown. If, during a second voltage application, the voltage rises and then drops while the ammeter needle swings violently, this is judged as arcing and results in non‑conformity.

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