The short-circuit method vacuum drying operation adopted by the miniature current transformer

After the vacuum drying operation of the short-circuit method of the miniature current transformer, it is necessary to use an insulation resistance meter to measure the insulation resistance of the primary and secondary windings to the ground, and then record the corresponding temperature. The vacuum drying operation of the short-circuit method of the miniature current transformer refers to the measurement of the volt-ampere characteristics in the state of the primary winding short-circuit. At this time, attention should also be paid to applying AC voltage to all protective windings in parallel to measuring the secondary winding, and the current is expressed to the rated current of the miniature current transformer, and the applied AC voltage value is recorded.

Miniature current transformers generally use oil-free drying on site, but some manufacturers believe that it is necessary to pay attention to electric heating when the product is full of oil, so that we can observe the temperature rise of the product. This is particularly important for miniature current transformers of 220kv and above. Because the insulation of these products is relatively thick, in the oil-free state, the conduction effect is poor, even if the temperature is low from the outside, the internal insulation may be aging due to overheating.

It is precisely because of this that when the miniature current transformer is in use, it should be noted that the product is energized and heated in the oily state, and the oil inside the product is drained for oil-free drying after the temperature rises and stabilizes. When it is in an oil-free vacuum state, the current through its primary winding shall not be higher than 70% of the rated current.

Pay attention to remove the metal expander, install a temporary cover plate with joints or valves for vacuuming, oiling and measurement; then also connect the primary winding in series, and use a copper wire of equal cross section to reliably short it; open it; For the secondary junction box, remove the external wiring. At this time, a double-arm bridge should also be used to measure the DC resistance of the secondary winding, 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.