The voltage transformer is also called the instrument transformer (PT). It is an instrument that changes the high voltage to a low voltage and maintains a certain relationship with the original phase. The working principle, construction and wiring method are the same as the transformer, but the capacity is small, usually only a few tens or hundreds of volts. Its purpose is to reduce the high voltage by a certain ratio, so that the low voltage coil can accurately reflect the change of the high voltage value to solve the difficulty of high voltage measurement. At the same time, because it reliably isolates high voltages, it ensures the safety of the surveyors and instruments and protection devices. In addition, the secondary voltage of the voltage transformer is 100V, which can standardize the instrument and relay.
The secondary short circuit of the voltage transformer will cause a large short-circuit current to the secondary coil, which will burn the voltage transformer coil, which will cause one or two breakdowns, so that the relevant protection will malfunction and the meter has no indication. Because the impedance of the voltage transformer itself is very small, the primary side is a constant voltage power supply. If the secondary short circuit occurs, a large short-circuit current will be generated in the secondary coil under the action of the constant voltage power supply, and the transformer is burned to damage the insulation. Second breakdown.
Loss of voltage transformer will cause the distance protection and voltage-related protection to malfunction. The meter has no indication and affects the safety of the system. Therefore, the voltage transformer cannot be short-circuited twice.
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