Current transformer short circuit vacuum drying

- Oct 14, 2019-

Current transformers are generally oil-free and dry at the site, but some manufacturers believe that the product should be energized with oil in order to observe the temperature rise of the product. This is especially important for current transformers of 220kv and above, because these products are relatively thick, and in the oil-free state, the conduction is poor, even if the temperature is low from the outside, and the internal insulation may be deteriorated due to overheating or even being smashed. focal. Therefore, it is preferable to energize and heat the product in an oiled state, and after the temperature rises and stabilizes, the oil inside the product is discharged to perform oil-free drying. In the case of oil-free vacuum, the current through the primary winding must not exceed 70% of the rated current.

The operational points are as follows:

(1) Remove the metal expander and install a temporary cover with a joint or valve for vacuuming, oiling and measuring

(2) Connect the primary windings in series and reliably short them with equal-section copper wires.

(3) i Open the secondary junction box, remove the external wiring, measure the secondary winding DC resistance with the double-arm bridge, record the corresponding temperature, and use this data as the reference value for calculating the average temperature of the secondary winding during the drying process.

(4) Measure the insulation resistance of the primary and secondary windings to the ground with an insulation resistance meter, and record the corresponding temperature

(5) Measure the volt-ampere characteristics in the case of a short-circuit of the primary winding. At this time, all the parallel windings of the protection windings are applied with an alternating voltage to measure the secondary winding <or primary winding). The current is expressed to the rated current of the transformer. And record the applied AC voltage value.

(6) A thermocouple is arranged at the exposed portion of the primary winding lead, at the short-circuit connection, and a thermometer is placed on the outer surface of the porcelain sleeve, the middle, the lower, and the top cover to measure and control the drying temperature.

(7) Connect the heating circuit and the vacuum line.