1. Main insulation and turn-to-turn insulation faults of windings
The main insulation and turn-to-turn insulation of transformer windings are the parts that are prone to failure. The main reasons are: due to long-term overload operation, poor heat dissipation conditions, or long service life, the insulation of the transformer windings is aging and brittle, and the electrical strength is greatly reduced; Insulation defects, once the voltage fluctuations are encountered, the insulation may be broken down; water in the transformer oil will greatly reduce the insulation strength and cannot withstand the allowable voltage, resulting in insulation breakdown; at the reinforced section of the high-voltage winding or the low-voltage winding part, Due to the expansion of the total package insulation, the oil passage is blocked, which affects the heat dissipation, and the winding insulation is aged due to overheating, resulting in a breakdown and short circuit; due to the imperfect lightning protection facilities, insulation breakdown occurs under the action of atmospheric overvoltage.
2. Lead wire insulation fault The transformer lead wire is drawn out through the inner cavity of the transformer casing and connected to the external circuit, and the lead wire is supported and insulated by the casing. Because the upper end cap of the casing (general cap) is not tightly closed and water enters, the main insulation of the lead is damaged by moisture, or the lead wire in the tank is exposed to the air due to the severe lack of oil in the transformer, causing internal flashover, which will cause failure at the lead wire. .
3. Iron core insulation failure The transformer core is made of stacked silicon steel sheets, and there is an insulating paint film between the silicon steel sheets. Due to the poor tightening of the silicon steel sheet, the paint film is destroyed and eddy current occurs, resulting in local overheating. In the same way, if the insulation of the core screws, weights and other components that clamp the iron core is damaged, overheating will also occur. In addition, if there are iron filings or welding slag remaining in the transformer, the iron core will be grounded at two or more points, which will cause the iron core to fail.
4. Transformer bushing flashover and explosion transformer high-voltage side (110kV and above) generally use capacitor bushing. Due to poor porcelain, there are trachoma or cracks; the capacitor core is defective in manufacturing, and there is free discharge inside; the bushing is not sealed. Good, there is oil leakage; serious casing fouling, etc., flashover and explosion may occur.
5. Tap changer fault Transformer tap changer is one of the common fault parts of transformers. The tap changer is divided into two types: no-load pressure regulation and on-load pressure regulation. The reasons for common failures are: 1) No-load tap changer: due to long-term contact by pressure, there will be insufficient spring pressure and uneven pressure on the rollers, which makes the tap changer. The effective contact area of the connection part of the tap changer is reduced, and the silver plating of the contact part of the connection part wears off, causing the tap changer to heat up and damage during operation; the tap changer has poor contact, poor connection and welding of the lead wires, and cannot withstand the short-circuit current. The impact causes the tap changer to be burned out by the short-circuit current and fails; due to poor management, the tap changer is disturbed or the work is careless, resulting in a tap changer accident. 2) On-load tap-changer: For transformers with on-load tap-changers, the oil tank of the tap-changer and the oil tank of the transformer are generally not connected to each other. If the oil tank of the tap changer is seriously short of oil, the short circuit fault of the tap changer will occur during switching, which will cause the tap changer to burn out. During the overhaul of the casing, the vacuuming is not complete, so that the air remains between the screens. After the operation, under the action of the high electric field, partial discharge occurs, and even the insulation layer is broken down, causing an accident.