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What are the working principles and characteristics of voltage transformers?

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Working principle:

Its working principle is the same as that of the transformer, and the basic structure is also the core and the primary and secondary windings. The characteristic is that the capacity is very small and relatively constant, and it is close to the no-load state during normal operation.

The impedance of the voltage transformer itself is very small. Once a short circuit occurs on the secondary side, the current will increase sharply and burn the coil. For this reason, the primary side of the voltage transformer is connected with a fuse, and the secondary side is reliably grounded, so as to avoid personal and equipment accidents caused by high potential to the ground on the secondary side when the insulation of the primary and secondary sides is damaged.

measuring voltage transformer is generally made into single-phase double coil structure, its primary voltage is the measured voltage (such as the line voltage of power system), can be used in single phase, can also be used in two V-V form for three-phase use. Voltage transformers used in laboratories are often multi-tapped on the primary side to meet the needs of measuring different voltages. The voltage transformer for protective grounding also has a third coil, called a three-coil voltage transformer. The third coil of the three phases is connected into an open triangle, and the two leads of the open triangle are connected with the voltage coil of the grounding protection relay.

During normal operation, the three-phase voltage of the power system is symmetrical, and the sum of the three-phase induced electromotive force on the third coil is zero. Once the single-phase grounding occurs, the neutral point appears displacement, the zero sequence voltage will appear between the terminals of the open triangle to make the relay act, thus protecting the power system. If zero sequence voltage appears in

coil, zero sequence magnetic flux will appear in the corresponding core. For this reason, this three-phase voltage transformer adopts the side yoke type iron core (10KV and below) or adopts three single-phase voltage transformers. For this transformer, the accuracy of the third coil is not high, but requires a certain over-excitation characteristics (that is, when the primary voltage increases, the magnetic flux density in the core also increases by a corresponding multiple without damage). [1]

Voltage transformer is an indispensable electrical appliance for power transmission and power supply systems such as power plants and substations.

precision voltage transformer is an instrument used to expand the volume limit and measure voltage, power and electric energy in the electric measuring laboratory.

voltage transformer and transformer are very similar, are used to transform the voltage on the line.


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