Voltage transformer - an indispensable device

Companies that deal with the purchase and sale of electricity, often keep a record of consumption of this resource, the magnitude of losses, as well as useful capacity. For such operations, current and voltage transformers are traditionally used. Such devices are able to work in high voltage networks without additional devices. Such equipment is intended for isolation of secondary circuits and connected to them measuring electrical appliances from high-voltage equipment. Small values of current and voltage make it possible to make such devices more compact and simple.

Current transformers (CTs) are used to convert large currents to small ones. They are suitable for measurements by various standardized instruments. In addition, it helps to protect the measuring circuit from the negative effect of short circuit.

According to the design, the following TTs are distinguished:

1. Supporting.

2. The bus.

3. Built-in.

4. Walkthrough.

5. Detachable.

6. Electrical clamps.

The current transformer is characterized by the following characteristics:

1. Frequency range suitable for operation.

2. Coefficient of transformation.

3. Accuracy class.

4. Accuracy.

5. Rated current.

6. The maximum current.

In turn, the voltage transformer (VT) is used to reduce the value to values suitable for measurements. Due to the electromagnetic connection of the primary and secondary windings of this equipment, the measuring circuits are isolated, as well as the separation of the relay protection equipment from the high-voltage network. To ensure the safety of electrical personnel operating these devices, one of the terminals of the secondary winding is grounded. A distinctive feature of the voltage transformer is that its normal operating mode is close to idle. In this case, the resistance value is large enough, and the current value, on the contrary, is small. Consequently, the short-circuit voltage of the transformer has the same deleterious effect.

Each TN has its own characteristics, which are expressed in terms of:

1. The error, which depends on the magnitude of the magnetic permeability and the design of the magnetic circuit. Reduce this figure can be, by reducing the number of turns in the primary winding, and also using compensating devices.

2. Accuracy class.

3. Coefficient of transformation.

4. The maximum voltage.

5. Rated voltage.

By design distinguish single-phase and three-phase TH. The first are applied at any voltage, the second - at a voltage of not more than 18000 V.
Isolated dry, oil and cast are used for the insulation used.
Unlike the current transformer, which is connected to the network in series, the measuring voltage transformer is connected by a primary winding parallel to the measured circuit.

The parameters of the measured circuit are determined as follows: the value displayed by the voltage and current transformer is multiplied by the transformation coefficient of the corresponding device.

The peculiarity of measuring transformers is that the possibility of the appearance of an open secondary winding is strictly excluded by the safety rules.