Common Faults Of Outdoor Distribution Transformer

Outdoor distribution transformer will inevitably have some faults during use.

1. The common faults of outdoor distribution transformers are mainly the main insulation and inter-turn insulation faults of the 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 fluctuates, it is possible to break down the insulation; water in the transformer oil greatly reduces 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 insulation failure:

The lead wire of the transformer is drawn out through the inner cavity of the transformer bushing and connected to the external circuit, and the lead wire is supported and insulated by the bushing. Because the upper end cap (general cap) of the casing is not tightly sealed 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. Core insulation failure:

The toutdoor distribution 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. Outdoor distribution transformer bushing flashover and explosion:

The high-voltage side of the transformer (110kV and above) generally uses capacitor bushings, which have trachoma or cracks due to poor porcelain; the capacitor core is defective in manufacturing, and there is free discharge inside; the bushing is not well sealed, and there is oil leakage; the bushing Severe fouling, etc., may cause flashover and explosion.

5. Failure of the tap changer:

Transformer tap changer is one of the common fault parts of transformer. The tap changer is divided into two types: no-load voltage regulation and on-load voltage regulation. The common faults are as follows:

1) No-load tap-changer: due to long-term pressure contact, there will be insufficient spring pressure and uneven roller pressure, which reduces the effective contact area of the tap-changer connection part, and the silver-plated contact part at the connection wears off, causing The tap-changer is damaged by heat during operation; the tap-changer is in poor contact, the connection and welding of the lead wires are poor, and the tap-changer cannot withstand the impact of the short-circuit current, causing the tap-changer to be burned out by the short-circuit current and malfunction; due to poor management, the adjustment is chaotic The tap or work carelessness caused the 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 outdoor distribution 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. For this reason, the oil level of the two fuel tanks should be monitored separately during operation, and the faults of the tap changer mechanism include: due to the jam, the tap changer stops at the process position, causing the tap changer to burn out; the oil tank of the tap changer is not tightly sealed As for water seepage and oil leakage, oil inspection and testing have not been carried out for many years, resulting in oil contamination and a great decrease in insulation strength, resulting in failure; the branch switch switching mechanism is not adjusted properly, the contacts are singed, and in severe cases, they partially melt, resulting in arc failure.