Three-phase transformer is used to convert voltage. The device is used in the field of electrification of industrial economy and domestic needs. In addition, such devices are indispensable on ships, as they are used to power devices of various denominations.
Calculation of a three-phase transformer is made in accordance with special documentation. Based on the received data, 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.
A three-phase transformer can be step-down or step-up, the conversion factor depends on the number of turns of both windings. The device can be assembled from three single-phase analogues or run on a common core, the sum of the magnetic fluxes of each phase in such a device will be equal to zero.
For industrial transformers, a series of tests are carried out for compliance with the specified parameters. A set of measures for checking the characteristics of the device includes measuring the resistance of each winding, checkinginsulation against earth and between phases. A special device energizes the windings and checks the penetration ability of the insulation. Next, voltage is applied to the primary winding and the output value is measured. With the help of this experience, the transformation ratio 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 piping and installation of equipment for switchgears of 110 kV and above is not allowed without the supervision of a specialist from the factory where the manufacture was made. In this case, the tests must be carried out according to accepted rules in the presence of a competent person.
Three-phase transformer is connected according to the "Star" scheme or according to the "Triangle" scheme. The star connection is implemented by a common node of the beginnings of all phases. The scheme in the form of a triangle is carried out by connecting the phases in series into a ring: the end of the first phase is connected to the beginning of the second, the end of the second to the beginning of the third and the end of the third to the beginning of the first.
If a three-phase transformer is connected according to the "Star" scheme, then the elements can be made with a dead-earthed or isolated neutral (this is the name of the node connecting the ends of the phases). For high-voltage switchgear, a special umbrella is used, which allows you to ground and unground the neutral. However, in switchgears for safety at 0.4 kV, a grounded zero is used.
Transformers are used to protect power linesvoltages that control the power supply. They help to orient the protection in terms of angles and values when adjusting the differential operation of devices. Three transformers per phase are most commonly used.
Each of them has at least two cores: one is connected into an open triangle, the other into a star. The star is used to measure the voltage on the lines, and the open triangle is needed as short circuit protection.
Today, voltage transformers are produced with the third core under the account. It is used to connect counters. As a rule, the third core is also connected in a star pattern. This separation of control circuits from accounting circuits helps to obtain more accurate readings, since the core accuracy class for the counter is higher.
