All about a three-phase transformer

A three-phase transformer is used to convert the voltage. A device is used in the field of electrification of industrial facilities and household needs. In addition, such devices are indispensable on ships, since they are used to power devices of different denominations.

The three-phase transformer is calculated in accordance with the special documentation. On the basis of the data obtained, the required equipment is selected. The device is used not only for industrial needs, but also in household appliances in the production of electronic control circuits.

The three-phase transformer can be decreasing or increasing, the coefficient of the converted values depends on the number of turns of both windings. The device can be assembled from three single-phase analogs or performed on a common core, the sum of the magnetic fluxes of each phase in such a device will be zero.

For industrial transformers, a number of tests are carried out for compliance with specified parameters. A set of measures to verify the characteristics of the device includes measuring the resistance of each winding, checking insulation against the ground and between phases. A special device supplies voltage to the windings and verifies the breakdown capacity of the insulation. The voltage is then applied to the primary winding and the output value is measured. Using this experience, the transformation ratio is calculated.

The results of measurements should correspond to the values reflected in the accompanying documentation, otherwise the three-phase transformer is rejected. It is very important to understand that the binding and installation of equipment for 110 kV and higher switchgears are not allowed without the supervision of a specialist from the factory where the manufacture was made. In this case, the tests should be carried out in accordance with the adopted rules in the presence of a competent person.

The three-phase transformer is connected according to the "Star" scheme or "Triangle" scheme. The star connection is realized by the common node of the beginnings of all phases. The scheme in the form of a triangle is carried out by a series connection of phases in a ring: the end of the first phase is connected with the beginning of the second, the end of the second with the beginning of the third and the end of the third with the beginning of the first.

If the three-phase transformer is connected according to the "Star" scheme, then the elements can be executed with a dull-earthed or isolated neutral (the so-called node connecting the ends of the phases). For high-voltage switchgears a special umbrella is used, which allows grounding and neutralizing the neutral. However, 0.4 kV earthing switches use grounded zero.

To protect power lines , voltage transformers are used to control the power supply. They help to orient the protection in corners and sizes when adjusting the differential of devices. Most often, three transformers are used per phase.

Each of them has at least two cores: one is connected to an open triangle, the other to a star. The star serves to measure the voltage on the lines, and an open triangle is necessary as a protection against short-circuiting.

Today, voltage transformers with a third core are produced under the account. It connects the counters. As a rule, the third core is also connected according to the star scheme. This separation of the control circuits from the counting circuits helps to obtain more accurate readings, since the accuracy class of the core for the counter is higher.