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Use and maintenance of dry-type transformers
Use and maintenance of dry-type transformers
Classification:News Time: 2020-11-11 11:47
【Summary】With the exception of individual product series, dry-type transformers with air as the insulating medium are less able to withstand impulse voltage than oil-immersed transformers. Therefore, their use conditions are generally limited to indoors that are not directly connected to overhead lines, so they will not be exposed to the atmosphere. Otherwise, special lightning protection should be added to ensure that the amplitude of atmospheric overvoltage does not exceed the amplitude of the power frequency test voltage.

With the exception of individual product series, dry-type transformers with air as the insulating medium are less able to withstand impulse voltage than oil-immersed transformers. Therefore, their use conditions are generally limited to indoors that are not directly connected to overhead lines, so they will not be exposed to the atmosphere. Otherwise, special lightning protection should be added to ensure that the amplitude of atmospheric overvoltage does not exceed the amplitude of the power frequency test voltage.

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Dry-type transformers should not be too long apart from manufacturing to putting them into operation to prevent the insulation from being damp, let alone being exposed to rain, otherwise it needs to be dried again.

The maintenance of the dry-type transformer body and the switching of the winding taps can be easily carried out by opening the outer casing of the transformer. It is also very convenient to observe and monitor the operating status of the transformer. During installation, a rubber pad is set between the transformer and the installation foundation to reduce the vibration and noise of the transformer.

Cast dry-type transformer

Use and maintenance

Features of cast dry transformer

(1) The winding is made of copper wire, and glass fiber is used to strengthen the thin insulating structure of epoxy resin pouring under vacuum.

(2) Class F insulation, with automatic temperature control system, and forced air cooling, which can increase the rated capacity by 50%.

Inspection after the cast dry-type transformer is put into operation

(1) Whether there is abnormal sound or vibration.

(2) Whether there is any discoloration caused by local overheating, harmful gas corrosion, etc., causing creepage traces and carbonization on the insulating surface.

(3) Whether the temperature in the house or cabinet where the transformer is located is particularly high, whether its ventilation and ventilation are normal, and whether the air-cooling device of the transformer is operating normally.

Regular inspection of cast dry transformer

(1) One inspection will be carried out 2 to 3 months after the operation, and once a year thereafter.

(2) Check whether there is dust accumulation, cracks, discoloration, discharge, etc. on the cast-in windings and interphase connecting wires, and whether the insulation resistance is normal.

(3) Check whether the iron core air duct is blocked by dust, foreign matter, rust or corrosion.

(4) Check whether the contacts of the tap changer are overheated, discolored, poorly contacted, or corroded.

(5) Check whether the winding compression device is loose.

(6) Check whether the pointer thermometer and other instruments and protection devices operate normally.

(7) Check whether the cooling device including the motor and fan bearings are in good condition.

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Types of dry-type transformers

According to different structures, dry-type transformers can be divided into open type, closed type and cast type.

(1) Open type. The open type is a commonly used type. Its body is in direct contact with the air. It is suitable for a relatively dry and clean indoor environment (when the ambient temperature is 20 degrees Celsius, the relative humidity does not exceed 80%), generally air-cooled and air-cooled 2 Kind of cooling method.

(2) Closed type. The body of the device is in a closed shell, not in direct contact with the outside air, and can be used in harsh environments. Due to poor sealing and heat dissipation conditions, it is mainly used in mines and other places. The closed type can also be filled with sulfur hexafluoride gas of 0.2-0.3 MPa, and forced to circulate, the insulation and heat dissipation capacity of the transformer is the same as the oil-immersed type, which is suitable for users with high voltage levels.

(3) Pouring type. Pouring epoxy resin or other resin as the main insulation, simple structure, small volume, suitable for users with smaller capacity.

Features of dry-type transformers

Since the insulation degree and heat dissipation performance of air are worse than that of oil, the effective material consumption of air-insulated dry-type transformers is higher than that of oil-immersed transformers. Therefore, the fire protection requirements are only higher in underground railways, high-rise buildings, workshops or power stations. Only use dry-type transformers in places where

Dry-type transformers with air insulation are less capable of withstanding impulse voltage than oil-immersed transformers. Dry-type transformer winding insulation adopts A, E, B, F, H, C heat resistance grades, and its temperature limits are respectively 60, 75, 80, 100, 125, and 150 degrees Celsius (all measured by resistance method). The surface of the iron core and the surface of the structural parts shall not exceed the allowable temperature rise of the insulating material (measured by the thermometer method). Because the body is exposed to the air, the winding immersion treatment is very important. In addition to the insulating paint, the winding must be coated with a moisture-proof covering paint.

 

Related Information

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Use and maintenance of dry-type transformers

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