Safe operation of power frequency withstand voltage test transformer
Date: 2025-09-08Read: 1
The safe operation of power frequency withstand voltage test transformers should follow the following key steps and precautions： -
Preparation and inspection before the experiment
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Personnel division and trainingTest personnel need to have clear division of labor, set safe distances, and receive professional training to obtain operation certificates. Operators and verifiers should stand on insulated mats to ensure safe operation.
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Equipment and grounding inspectionCheck whether the test transformer and supporting equipment (such as operation box and voltage regulator) are intact, and the grounding system must be correct and reliable. The outer shell of the test transformer, the high-voltage tail X end, and the measuring winding F end all need to be grounded to prevent potential differences from causing danger.
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Subject handlingThe main parts of the test sample should be cleaned and kept dry to avoid experimental numerical errors or insulation breakdown caused by surface dirt or moisture.
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Air lift testBefore testing large equipment, it is necessary to conduct an air lift test (to increase the voltage to the test voltage without connecting the test sample) to calibrate the instrument accuracy, adjust the discharge ball gap spacing, and ensure the accuracy of the protective device.
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Environment and tool inspectionThe test site should have good ventilation, dry ground, and no gas or chemical dust that affects insulation. The tools used must be safe and reliable, and tools with poor insulation performance must be replaced immediately.
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Operation specifications during the experiment
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Boost and buck control：
- Boosting must start from zero (or close to zero), and it is forbidden to impact the closing (such as sudden closing of the regulator when it is not at zero). The boosting speed should be uniform, starting from 75% of the test voltage and boosting at a rate of 2% of the test voltage per second.
- During the boosting process, closely monitor the readings of the voltmeter and ammeter, as well as the status of the test sample, for any abnormal noises. If the pointer of the voltage/current meter swings greatly, the insulation burns and smokes, or the test sample makes abnormal sounds, the voltage should be immediately reduced, the power should be cut off, and the cause should be identified.
- After the withstand voltage time is up, quickly and uniformly reduce the voltage to zero, and then cut off the power supply. It is forbidden to directly cut off the power under high voltage.
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exception handling：
- In case of personal danger or equipment abnormalities (such as discharge or breakdown) during the experiment, the power should be immediately cut off by pressing the stop button, and necessary measures should be taken (such as fully discharging the test sample).
- If the test is interrupted (such as a power outage), a full time withstand voltage test must be conducted again after restoring the power supply, and the remaining time cannot be supplemented alone.
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Post test maintenance and recording
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Equipment discharge and disconnectionAfter the experiment is completed, all switches should be turned off first, and the operator should leave the control room. After confirming that there is no power, the high-voltage part of the equipment should be grounded, and then the test sample should be removed. The test sample should be fully discharged before contact to prevent residual voltage from injuring people.
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Data organization and analysisOrganize test data (such as voltage, current, withstand time), analyze test results, and provide a basis for evaluating the insulation condition of equipment. If the test fails, it is necessary to report to the relevant department and take corrective measures.
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Equipment maintenance and recordingCheck the testing equipment (such as the wear of the regulator carbon brush) and replace damaged parts in a timely manner. Clean up equipment and site hygiene, fill in equipment operation records and test record forms.
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Safety protection and emergency measures
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Personal protective equipmentTest personnel are required to wear insulated gloves, insulated shoes, protective goggles and other personal protective equipment to prevent electric shock or arc burns.
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Safety Warning and IsolationSet up fences and warning signs in the experimental area, and unrelated personnel are not allowed to enter. During the experiment, walking or making loud noises is strictly prohibited to avoid interfering with the operation.
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emergency preparednessEquip emergency equipment such as fire extinguishers and first aid kits, and ensure that the testing personnel are familiar with the usage methods. When a fire occurs, immediately cut off the power and use a dry powder fire extinguisher to extinguish the fire. It is forbidden to use water to extinguish the fire.
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Special scenario precautions
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Large capacity sample testFor large capacity test samples such as capacitors and ultra long cables, it is necessary to slowly increase the voltage to prevent excessive charging current from burning out the microampere meter. If necessary, gradually increase the voltage and read the stable readings of the microampere meter at each voltage.
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Outdoor experimentOutdoor testing is prohibited during thunderstorms to avoid damage to equipment caused by lightning strikes. Before the experiment, check the weather forecast and select a period of no wind or rain.
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Oil filling equipment testOil filled equipment (such as transformers) should be left to stand for sufficient time after oil injection (24 hours for 110kV and below, 48 hours for 220kV, 72 hours for 500kV) before being pressurized to avoid insulation breakdown during withstand voltage.