Fault types and treatment methods of power transformer
Writer： Hengfeng you electric Time：2023-04-06 views：times
The common faults of transformer in operation include the faults of winding, bushing, tap changer, iron core, oil tank and other accessories.
1. Winding fault
It mainly includes inter turn short circuit, winding grounding, phase to phase short circuit, wire breakage and joint welding.
(1) Interturn short circuit: short circuit fault caused by insulation damage of winding wire itself. The phenomenon of interturn short circuit fault is that when interturn short circuit occurs, the overheated oil temperature of the transformer increases and the current at the power side increases slightly; Sometimes there is a "squeak" sound and a "gurgle" sound in the oil. When it is serious, the conservator injects oil; The cause of inter turn short circuit fault is that the inter turn insulation is damaged due to the long-term overload of transformer operation.
(2) Winding grounding: winding grounding refers to the partial short circuit between winding and grounding. When the winding of the oil immersed test transformer is grounded, the oil quality of the transformer becomes bad, and the grounding for a long time will aging and damage the insulation of the grounding phase winding. The causes of winding grounding, lightning atmospheric overvoltage and operating overvoltage make the winding deform under the impact of short-circuit current, and the main insulation is damaged and broken; The insulation strength of transformer oil decreases after being affected with moisture.
(3) Phase to phase short circuit: phase to phase short circuit refers to the short circuit caused by the breakdown of the insulation between windings. When the phase to phase short circuit occurs, the transformer oil temperature increases sharply, and the switch on the three sides of the oil conservator oil injection main transformer trips. The transformer phase to phase short circuit is caused by the aging of the main insulation of the transformer, the reduction of the insulation, the low breakdown voltage of the transformer oil, or the expansion of other faults, such as inter turn short circuit and grounding fault of the winding, Due to the scattering and splashing of arc and molten copper (aluminum) particles, the accident spread and expanded into phase to phase short circuit. In case of phase to phase short circuit, it should be reported to the dispatcher on duty and the superior leader immediately, and the maintenance department should find out the cause of the fault in time and deal with it, so that the transformer can resume operation as soon as possible.
(4) Winding and lead wire breaking: when the winding and lead wire are broken, the arc often occurs, which causes the decomposition and gasification of transformer oil, and sometimes causes phase to phase short circuit. The reasons are mostly due to poor welding in the wire, overheating and fusing, or inter turn short circuit and burnout, as well as winding breaking caused by short-circuit stress.
2. Casing failure
The fouling of transformer bushing causes pollution flashover in heavy fog or light rain. The oil immersed test transformer makes the single-phase grounding or phase to phase short circuit on the high-voltage side of the transformer.
3. Serious leakage
The oil leakage of the transformer during operation is serious or continuously overflows from the damaged place so that the oil level gauge cannot see the oil level. At this time, the transformer should be stopped immediately for leakage repair and refueling. The reasons for the oil leakage of the transformer are weld cracking or seal failure, and the oil tank is seriously rusted and damaged by external force of vibration during operation.
4. Tap changer failure
Common faults include poor contact or inaccurate position of tap changer, melting and burning of contact surface, discharge of interphase contacts or discharge of each tap.
(1) No load tap changer failure: the spring pressure of the no load tap changer is insufficient, the roller pressure is uneven, the contact is poor, and the effective contact area is reduced. In addition, there is oil stain at the contact of the switch, and the contact resistance increases, which will cause the contact surface of the tap changer to be burned during operation. If the outgoing line is poorly connected or welded, when it is impacted by short-circuit current, it will cause the tap changer to fail. The oil immersed test transformer has the wrong number of the tap changer, After voltage regulation, it cannot meet the predetermined requirements, resulting in three-phase voltage imbalance, circulating current, increased loss, and transformer failure. The phase to phase insulation distance of the tap board of the tap changer is not enough, and there is oil sludge accumulated on the insulation material to become damp. When overvoltage occurs, it will also cause the fault of phase to phase short circuit of the tap changer.
(2) Fault of on load tap changer: when the sealing of on load tap changer is not tight, the interphase short circuit of the tap changer will be caused by the intrusion of rainwater. The current limiting impedance of the tap changer may be broken down and burned out during the switching process. The arc between the contacts may be longer and longer, which will expand the fault and cause transformer fault. Because the roller of the tap changer is sometimes stuck, the tap changer stops at the transition position, resulting in interphase short circuit. Because the additional oil tank of the tap changer is not sealed tightly, the oil in the oil tank is connected with the oil in the transformer, so that the oil level indication of the tap changer has a false oil level, which cannot meet the standard requirements. When the tap changer is operated with power, it will endanger the safe operation of the tap changer.
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