The power frequency withstand voltage test may appear to involve only three actions: "voltage rise, wait, and voltage drop," but the execution quality of each step significantly impacts safety and the reliability of the results. Taking the HZG series dry-type test transformer as an example, let's outline the complete operation process.

Step 1: Ensure reliable grounding of the high-voltage tail

This is the primary task before the test. The manual clearly states: Before the test, the high-voltage tail of the test transformer (marked with the symbol "┻") must be reliably grounded; otherwise, it will endanger personal and equipment safety. After grounding the high-voltage tail, a grounding circuit is formed on the high-voltage side, ensuring the safety of the test personnel and serving as the reference potential for the high-voltage measurement circuit.

Step 2: Conduct an empty test of the equipment

After connecting all the lines, do not connect the test specimen yet. Conduct a no-load test on the control box and test transformer—confirm that the voltage regulator can smoothly raise the voltage from zero, the protection circuit functions properly, the voltmeter and ammeter operate normally, and there are no abnormal sounds or odors. Once the no-load test is confirmed correct, then connect the test specimen.

Step 3: Apply uniform pressure and monitor continuously

Turn off the power, press the closing button, and rotate the voltage regulator knob clockwise evenly to slowly increase the voltage to the specified stage value. Monitor the voltmeter reading and the condition of the test specimen closely. Avoid rapid or stepwise voltage increases.

Step 4: Maintain pressure and monitor

After reaching the test voltage, maintain the specified withstand time (typically 1 minute), continuously monitor the ammeter and the test specimen, and immediately cut off the power supply if there is a sudden current surge, smoke, odor, flashover, or similar conditions.

Step 5: Rapidly return to zero and discharge

The withstand voltage time has expired. Observe the voltmeter and quickly return the voltage regulator to zero, then cut off the high voltage. Next, discharge the test specimen using a discharge rod through a current-limiting resistor, followed by direct grounding discharge. Only after confirming no residual charge remains can the wiring be disconnected.