Inspection and identification methods for transformer on-load tap changer (OLTC) faults

According to statistics, the faults of the on-load voltage regulating switch of the transformer mainly include two aspects: First, the failure of the voltage regulating switch driving mechanism, mainly including the linkage of the electric mechanism, water intrusion into the box, oil leakage from the gear box, insufficient spring energy storage, etc. The second is the failure of the switch body, which mainly includes oil leakage from the oil chamber, loose fasteners, stuck contact motion, and poor contact caused by contact wear. The common fault types of on-load voltage regulating switches are listed and analyzed below.

1. Switch driving mechanism failure

① Motor failure. When the operating power supply loses power or there is a problem with the motor circuit, it will cause the switch motor mechanism to malfunction, causing the lifting contacts to be unable to move.

②The elasticity of the spring energy storage mechanism becomes weaker. The long-term deformation operation of the spring, coupled with the thermal effect of the current, weakens the elasticity of the spring, causing the transmission mechanism to fail to reach the desired position.

2. Switch body failure

①The contact is heated and worn. The on-load voltage regulating switch carries the load current to realize voltage regulation. During the voltage regulation process, the gear position is changed, causing problems such as mechanical wear and electrical corrosion of the contacts. The contact resistance of the contacts increases and the heat generation increases, which accelerates the corrosion and mechanical deformation of the contact surface, resulting in damage to the switch.

②The switch refuses to move or does not switch in place. The switch cannot switch in place due to insufficient power or obstruction, and stays in the middle position for a long time, which can cause the transition resistor to continue to heat up, causing the transformer to trip and interrupt the power supply.

③ Oil leaks from the oil chamber. The oil chamber of the on-load tap-changer is an independent oil tank. During operation, the oil in the oil chamber of the on-load tap changer is not allowed to enter the transformer body. An arc is generated when the transfer switch is operating, which deteriorates the quality of the oil in the oil chamber. This oil cannot enter the transformer body.

④Deterioration of oil quality. The arc generated during the operation of the on-load voltage regulating switch causes the oil quality to deteriorate and the insulation level of the switch to decrease. Transformer oil has the functions of insulation, arc extinguishing, cooling, lubrication, and anti-corrosion. The deterioration of oil quality will produce free carbon, hydrogen, acetylene and other gases and grease. Most of the gas will generally be discharged from the insulating oil, but some of the free carbon particles and grease will be mixed in the insulating oil, and the other part will accumulate on the surface of the insulating parts of the switch, reducing the insulation level of the switch. The voltage regulating switch of the transformer is a rotatable part of the transformer. It is easy for the machine to heat up due to poor contact and cause malfunctions. For this kind of switch failure that is easy to occur, we must be prepared to deal with it. This kind of failure can usually be solved from the following Several aspects to check and judge:

(1) Check whether there are burn marks (singing) and poor contact on the fixed and movable contact surfaces, and whether there is sludge accumulation at the contact areas.

(2) Whether the transmission mechanism of the voltage regulating switch is flexible; whether the transmission mechanism is too loose so that the pointer tip on the box cover is indicated on the position mark, and the contacts are not closed at this time; whether the three-phase contacts of the switch are closed at the same time. on the spring, whether the tightness of the spring is the same.

(3) Check whether the seam between the operating lever of the switch and the box cover is tightly joined, and whether the gasket is complete; whether there is any water stain under the hole in the box cover where the operating lever is aligned.

(4) If a wiring board-type tap is used, the tightness of the wiring bolt pile heads should be checked, and whether there is accumulation of sludge between the wiring pile heads. Make sure that the pile heads are clean and intact, otherwise short circuits or flashes will easily occur. network traces.

(5) When inspecting the transformer on-load switch, the core part of the switch should be taken out and rotated back and forth to observe whether its contact limit action is smooth and consistent. At the same time, check its transition resistance to determine whether its connection is stable and reliable.

Weshine Electric Manufacturing Co., Ltd.