Wiring principle of capacitive Voltage Transformer (II)

 Characteristics

     Compared with electromagnetic voltage transformer, capacitive voltage transformer has the advantages of high impact insulation strength, simple manufacture, light weight, small volume, low cost, reliable operation, convenient maintenance and can also be used as coupling capacitor for high frequency carrier communication. The main drawback is that its error characteristic is worse than that of electromagnetic voltage transformer, and the output capacity is smaller, and there are many factors influencing the error (such as temperature, frequency, etc.). At present, the accuracy of YDR capacitive voltage transformer made in China has been improved to 0.5, and has been widely used in 110 KV and above neutral direct grounding system.

 Capacitive voltage transformer connection

       Capacitive voltage transformer wiring diagram: in a neutral ungrounded or arc-suppression coil grounded system, in order to measure the relative voltage of PT primary winding must be connected to star grounding

     In the power network of 3C60KV, three single-phase and three-winding voltage transformers or a three-phase five-column voltage transformer are usually used. It must be pointed out that this measurement cannot be done with a three-phase three-column voltage transformer. When the single-phase earthing short circuit occurs in the system, there will be zero sequence current passing through the three-phase of the transformer, which will produce the zero-sequence flux of the same size and the same phase. In the three-phase three-column transformer, the zero-sequence flux can only form a closed magnetic circuit through the air gap with large magnetoresistance and the iron shell. The zero-sequence current is very large, which causes the transformer windings to overheat and even damage the equipment. In the three-phase five-column voltage transformer, the zero-sequence flux can pass through the two sides of the core to form a loop, the magnetoresistance is small, so the zero-sequence current value is small, and does not cause damage to the transformer.