Oil free drying is generally used in the field of current transformer, but some manufacturers believe that the product should be heated by electricity in order to observe the temperature rise of the product. This is particularly important for 220kV and above current transformers, because these products have a thick insulation and poor conduction in an oil free state, even if the temperature is low from the outside, and the internal insulation may be ageing and even disturbed by overheating. Therefore, it is best to heat the product with oil in the condition of oil. After the temperature rises and tends to be stable, the oil inside the product is released to carry out oil-free drying.  In an oil-free vacuum state, the current of the primary winding shall not exceed 70% of the rated current.

The main points of operation are as follows:

(1) dismantle metal expander and install temporary cover plate with joints or valves for vacuuming, oil filling and measuring.

(2) connect the primary winding in series and connect it reliably with the copper conductor of equal cross section.

(3) I open two junction boxes, dismantle the external connection, use the double arm bridge to measure the secondary winding DC resistance and record the corresponding temperature, which is used as the datum for calculating the average temperature of the two winding during the drying process.

(4>) insulation resistance meter is used to measure the insulation resistance of the one or two winding to the ground, and record the corresponding temperature.

(5) measuring the volt ampere characteristic under the condition of primary winding short circuit. At this time, all the parallel windings of the protection winding are applied to AC voltage to measure the two winding < or primary winding. The ammeter reaches the rated current of the transformer. And record the applied voltage of the AC voltage.

(6) a thermometer is set up at the bare part of the winding lead, and the thermocouple at the short circuit line and so on. The thermometer is set up on the outer surface of the porcelain sleeve, in the middle, the lower and the top cover to measure and control the drying temperature.

(7) a good heating circuit and a vacuum pipeline are connected.

Add: No.38 South Taoyuan Road, Yaozhuang Town,Jiashan County, Jiaxing City, Zhejiang Province, China
Contact person: Elva Zhuang&Sunny Ni
Tel:+86-573-84775555
Fax:+86-573-84776699
Phone:+86-13732570078
E-mail:sales9@great-relay.com
       sunny.ni@great-relay.com