How to dry transformer?

Transformer is the principle of electromagnetic induction to change the AC voltage of the device. The main components are the primary coil, secondary coil and iron core (magnetic core).

The purpose of drying transformer is to remove water from the transformer insulation material and increase the insulation resistance to improve its flashover voltage. Transformers above 3kV must be dried. The transformer body is mainly composed of an iron core , a coil and an insulating material. After assembled, transformer must through the drying process to remove the water and gas of insulating materials before joining the transformer oil. It is to ensure the transformer insulation strength and service life enough. For high voltage transformer, the insulation material should be less than 0.5%. 

1. Induction heating method

The instrument itself is placed in the tank, the use of fuel tank wall eddy current loss of heat to dry. At this time the wall temperature should not exceed 115-120 degrees, the body temperature should not exceed 90-95. In order to winding the coil of convenience, as far as possible the number of turns of the coil less or less current, the wire can be  35-50mm2 wire, the general current is 150A. The oil tank wall can be filled with a plurality of asbestos bars, and the wire is wound on the asbestos strip.

2. Hot-air drying

The transformer itself is placed in a dry room through the hot air drying. The inlet hot air temperature should be increased gradually, and the filter should be installed at the inlet of hot air to prevent the entry of Mars and dust. The maximum temperature should not exceed 95. Hot air blowing device not directly, as uniform as possible from the body of the wind in all directions, so that the moisture released by the box cover hole.

Problems should be paid attention to in transformer drying:

(1) If the drying chamber is not vacuum, the vent should be opened on the lid of the box or the throttle hole can be used to make the moisture release.

(2) When the oil is heated, the insulation layer should be installed outside the tank. The insulating layer can be made of insulating material such as asbestos cloth, glass cloth and so on.

(3) In order to improve the drying quality of windings, there are two major factors to be considered: the first is to control the drying temperature; the other is to improve the vacuum of the equipment. On the first point, the general drying equipment can meet the technical requirements, to second points, subject to a number of factors, must be taken into account, reasonable arrangements in order to achieve good drying effect.

(4) The process of vacuum drying, drying in low temperature stage, not in the vacuum or low vacuum drying conditions, otherwise it is not conducive to the elimination of core temperature and moisture. When the temperature rose to 70 to 80 to improve the vacuum degree. When drying is carried out from 1 to 2h, the water vapor in the oil tank is more, the heat radiation ability is improved, the internal temperature tends to be uniform, the water is gradually reduced, and the heat radiation ability is reduced.

      (5)A method of identification of insulation after drying and transformer technical specifications for the test.

 After the transformer is dry, it is necessary to use insulation resistance tester to make a comprehensive identification of its insulation performance to check its drying effect. Identification of the project, in addition to casing, the rest are the same as the hoisting of the heart of the test items.