A three-phase transformer is used to convert voltage. The device is used in the field of electrification of industrial facilities and domestic needs. In addition, such devices are indispensable on ships, since they are used to power devices of various ratings.
Three-phase transformer is calculated in accordance with special documentation. Based on the data received, the necessary equipment is selected. The device is used not only for industrial needs, but also in household appliances in the production of electronic control circuits.
A three-phase transformer can be step-down or step-up, the ratio 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 series of tests are carried out for compliance with the specified parameters. A set of measures to verify the characteristics of the device includes measuring the resistance of each winding, checking the insulation relative to the ground and between the phases. Using a special device, voltage is applied to the windings and the breakdown ability of the insulation is checked. Next, voltage is applied to the primary winding and the output value is measured. Using this experience, the transformation coefficient is calculated.
The measurement results must correspond to the values ​​reflected in the accompanying documentation, otherwise the three-phase transformer is rejected. It is very important to understand that the strapping and installation of equipment for switchgear 110 kV and above are not allowed without the supervision of a specialist from the factory where the manufacture was made. In this case, tests should be carried out in accordance with the rules in the presence of a competent person.
The three-phase transformer is connected according to the "Star" scheme or according to the "Triangle" scheme. The star connection is realized by a common node of the beginnings of all phases. The scheme in the
form of a triangle is carried out by a serial connection of phases into a ring: the end of the first phase is connected to 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 a three-phase transformer is connected in accordance with the “Star” scheme, then the elements can be made with a grounded or insulated neutral (this is the name of the unit connecting the ends of the phases). For high-voltage switchgear, a special umbrella is used that allows you to ground and ground the neutral. However, 0.4 kV safety switchgears use a grounded zero.
To protect power lines , voltage transformers are used to control power supply. They help to orient the protection in angles and sizes when adjusting the differential response of devices. Most often, three transformers are used for each phase.
Each of them has at least two cores: one connects into an open triangle, the other into a star. The star is used to measure voltage on the lines, and an open triangle is necessary as protection against short circuits.
Today, voltage transformers with a third core are produced. With its help, the meters are connected. As a rule, the third core is also connected according to the pattern of the star. This separation of control circuits from accounting circuits helps to obtain more accurate readings, since the core accuracy class for the counter is higher.