The operating principle of the voltage transformer is the same as that of the transformer. Characteristic is small capacity and relatively constant, positive
Normal operation is close to no-load status.
The impedance of the voltage transformer itself is very small. Once a short circuit occurs on the side, the current will increase sharply and the coil will burn down. Therefore, the original side of the voltage transformer
It is connected with a fuse, and the auxiliary side is reliably grounded, so as to avoid the damage of the insulation of the original side and the auxiliary side.
Voltage transformers used for measurement are generally made into single-phase double-coil structure, and their original side voltage is measured voltage (such as line voltage of power system), which can be single-phase
Use, also can use two to join into v-v shape for three phase use. The voltage transformers used in the laboratory are usually multi-tap on the original side to adapt to the measurement
Same voltage requirement. The voltage transformer for protection ground also has a third coil, which is called the three-coil voltage transformer.
The third coil of the three-phase is connected to an open triangle, and the two leading ends of the open triangle are connected to the voltage coil of the ground protection relay.
In normal operation, the three-phase voltage of the power system is symmetric, and the sum of the three-phase induction electromotive force on the third coil is zero. Once single-phase grounding occurs,
When the neutral point is displaced, the zero sequence voltage between the terminals of the open triangle will cause the relay to act, thus protecting the power system.
If the coil has zero sequence voltage, the corresponding zero sequence flux will appear in the corresponding core. For this reason, the three-phase voltage transformer USES a side yoke core (10KV)
And below) or three single-phase voltage transformers. For this kind of mutual inductor, the accuracy of the third coil is not high, but there are certain requirements
Overexcitation characteristic (that is, when the original side voltage increases, the flux density in the core increases by a corresponding multiple without damage).
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