The partial discharge-free test transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are the primary coil, secondary coil, and iron core (magnetic core). Its main functions include voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc.
(1) When replacing insulation parts, ensure the performance of the insulation parts.
During handling, the performance of the replaced insulation parts should be tested and meet the requirements before use. 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 of time to ensure the insulation of the wooden blocks.
(2) Pay attention to the sharp corners when reinstalling the iron core.
When reinstalling the upper yoke, attention should be paid to the sharp corners of the core laminations, and the inter-duct insulation should be measured promptly. Special attention should be paid to the sharp corners of the laminations at the oil duct to prevent lamination bridging causing multiple grounding points of the core. For example, in a 120MVA 220kV transformer, when replacing the low-voltage side winding and reinstalling the upper yoke, due to not paying attention to the sharp corners of the laminations and not measuring the inter-duct insulation in time, the inter-duct insulation was measured as 0 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 winding of the partial discharge-free test transformer is mainly determined by the following two aspects: first, the mechanical strength of the winding itself determined by its structural factors; second, the mechanical strength determined by the support of the inner diameter side of the winding, the axial compression structure of the winding, and the manufacturing process of pull plates and clamps.
(4) Drying of the partial discharge-free test transformer.
Since the transformer generally requires a long time for maintenance after being impacted by a short circuit, two measures can be taken to prevent the transformer from getting damp:
First, before finishing work each day, cover the transformer and use a vacuum pump to evacuate it to remove free water on the surface of the transformer body. When starting work the next day, use dry nitrogen or dry air to break the vacuum. Generally, after maintenance, the transformer can be put into operation directly after hot oil circulation for 24 hours;
Second, after finishing work each day, take rainproof measures for the transformer. After all work is completed, use the hot oil spray method to dry the transformer. This method generally takes 7-10 days.
Note: The above information and technical parameters are compiled and published by Yangzhou Darui Electric Co., Ltd.
