Precautions in Short-Circuit Fault Handling of Partial Discharge Test Transformer



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The partial discharge test transformer is a device that changes AC voltage based on the principle of electromagnetic induction, with main components being the primary coil, secondary coil, and iron core (magnetic core). Its main functions include voltage transformation, current transformation, impedance transformation, isolation, and voltage stabilization (magnetic saturation transformer), etc.

　　(1) When replacing insulating parts, ensure their performance.

　　During handling, test the performance of the replaced insulating parts and only use them if they meet requirements. Special attention should be paid to the insulation of the lead support wooden blocks. Before installation, the wooden blocks should be immersed in hot transformer oil at about 80°C for a period to ensure their insulation.

　　(2) Pay attention to sharp corners when reinstalling the iron core.

　　When reinstalling the upper yoke, pay attention to the sharp corners of the core laminations and promptly measure the insulation between oil ducts, especially at the sharp corners of the laminations near the oil ducts, to prevent multi-point grounding of the core due to lamination overlap. For example, in a 120MVA 220kV transformer, when replacing the winding on the low-voltage side and reinstalling the upper yoke, failure to pay attention to the sharp corners of the laminations and failure to promptly measure the insulation between oil ducts resulted in zero insulation resistance after installation. It took a long time to find that the sharp corners of the core laminations had short-circuited the oil duct.

　　(3) Replace winding materials with stronger short-circuit resistance and improve the structure.

　　The mechanical strength of the partial discharge test transformer winding is mainly determined by two aspects: first, the mechanical strength determined by the winding's own structural factors; second, the mechanical strength determined by the support on the inner diameter side of the winding, the axial compression structure of the winding, and the manufacturing processes of the pull plates and clamps.

　　(4) Drying of the partial discharge test transformer.

　　Since the transformer usually requires a long time for repair after a short-circuit impact, to prevent the transformer from getting damp, two measures can be taken:

　　First, before finishing work each day, cover the transformer and use a vacuum pump to evacuate it, removing free water on the transformer body surface. When starting work the next day, use dry nitrogen or dry air to break the vacuum. Generally, after repair, the transformer can be put into operation directly after hot oil circulation for 24 hours;

　　Second, after finishing work each day, take rain protection measures for the transformer. After all work is completed, use the hot oil spray method to dry the transformer, which generally takes 7-10 days.

　 Note: The above information and technical parameters are compiled and released by Yangzhou Dare Electric Co., Ltd.