Common problems and solutions in the operation of on-load tap changers of transformers:

 Common problem 1: Oil leakage in the oil chamber of the diverter switch

The diverter switch oil compartment is an independent oil tank. During operation, the oil in the oil chamber of the diverter switch is absolutely not allowed to enter the transformer body. This is because a certain arc is generated during the operation of the diverter switch, which causes the oil in the oil chamber to deteriorate. This kind of oil can only be stored in the oil chamber of the diverter switch. It can not be used in the transformer body. Once entered, it will seriously affect the chromatographic analysis of the internal oil of the transformer, that is, the judgment of the internal fault of the transformer. The reasons that cause oil leakage in the oil chamber of the diverter switch are:

⑴The oil drain valve at the bottom of the oil tank of the on-load tap-changer is not tightened, causing the oil in the oil tank of the transformer body to mix with the oil tank of the on-load tap-changer.

⑵The sealing rubber gasket material between the two fuel tanks is not good or the assembly process is not good. During the on-site treatment, it was found that most of the rubber pads were not properly selected due to the size of the rubber pads, and there was no margin after compression, and the rubber pads did not work. In addition, the upper edge of the oil tank of the on-load tap changer is misaligned with the reserved hole of the main oil tank, making it more difficult to seal. In some cases, the upper edge of the insulating cylinder of the oil tank of the on-load tap-changer was fractured, causing a gap to cause oil leakage.

⑶The oil seal of the center drive shaft is not tight.

Solution: Pay close attention to the oil level of the tap changer oil conservator during operation. When the oil level of the oil conservator of the transformer rises or falls abnormally, check whether the oil chamber of the diverter switch leaks. Regularly take oil samples for the transformer. If the chromatographic analysis of the main transformer hydrogen, acetylene and total hydrogen content is found to be abnormally high, check whether the oil chamber of the diverter switch leaks, so as to deal with it in time.

Frequently Asked Question 2: The contact hair inside the switch is hot

Frequent voltage adjustment will cause serious mechanical wear, electrical corrosion and contact pollution between the contacts, especially for transformers with large load currents. The thermal effect of the current will weaken the elasticity of the spring, and the contact between the moving and static contacts will become weaker. The contact pressure decreases, the contact resistance increases, and the heat generation between the contacts increases. The heat accelerates the oxidation corrosion and mechanical deformation of the contact surface, and forms a vicious circle, resulting in damage to the diverter switch.

Treatment method: Test the DC resistance of each tap position of the switch separately before the maintenance and operation, and measure the contact resistance of the contacts during the maintenance of the hanging cover, and check whether the coating and contact of the contacts are good. Rotate each gear position of the tap changer several times a year in conjunction with maintenance or testing to remove the influence of oxide film or oil stains and make good contact.

Common problem 3: Transition resistance disconnection and looseness

The disconnection and looseness of the transition resistance will cause the entire transformer to burn out. If the transition resistance is switched with load when it is blown, not only will the load current be interrupted, but also all phase voltages will appear on the fracture of the transition resistance and between the openings of the moving and static contacts. This voltage will not only break down the fracture of the resistor, but also generate a strong arc when the moving and static contacts are disconnected, which will cause a short circuit between the two taps of the transformation, and cause a short circuit and burn out of the high-voltage winding sub-connection section. At the same time, the arc quickly decomposes the oil in the switch oil chamber, producing a large amount of gas. If the safety protection device cannot discharge these gases immediately, the switch will be damaged. The energy of the arc can also burn the switch insulation cylinder, making the switch irreparable.

Treatment method: strengthen the inspection of transition resistance

⑴Before the transformer leaves the factory, before operation, and after overhaul, it is necessary to check whether the transition resistance is loosened, and whether the resistance wire is mechanically damaged, so as to avoid local overheating and burning during switching.

⑵For the on-load switch with switching times of more than 20,000 times or operating for more than 2 years, it is necessary to check whether the material of the transition resistor becomes brittle, whether the resistance has changed value, and whether the fastening is loose.

(3) When the transformer is switched at a high current of more than 2 times the rated current during operation, it is necessary to check whether the transition resistance is burned out.

⑷The situation that the overload and load switch does not switch occurs, that is, the main spring of the fast mechanism is fatigued or fractured and does not work, the transmission system is damaged, the fastener is loose, the mechanical jam, the limit failure, etc. When the time is extended beyond the specified value, it is necessary to check whether the transition resistance is burned out.