RU1827036C - Three-phase potential transformer - Google Patents

Abstract

The invention relates to grounded voltage transformers. The transformer contains three primary and three secondary windings, the connection schemes of which match. The first primary winding 1 is connected between the first two phase terminals and has a branch. A second primary winding 2 is connected between this branch and the third phase terminal. The second winding 2 has a branch between which a third primary winding 3 is connected and a grounded terminal. The transformer is resistant to ferroresonance with single-phase mains shorting to the ground through a moving arc. Its increased reliability is maintained even when expanding the field of application from 6-10 to 35 kV. Reliability is maintained by reducing the EMF of the equivalent source of the network capacitance acting in the discharge circuit through a voltage transformer. 1 C.p. f-ls, 1 ill. o / OS 00 hO VI О О О О)

Description

The invention relates to electrical engineering, in particular to grounded voltage transformers.

The purpose of the invention is to expand the scope of the transformer.

The drawing shows a connection diagram of transformer windings.

The transformer contains three primary windings 1, 2 and 3. The primary winding 1 has a branch and is connected to the first (for example, C) and second (for example, B) phase terminals of the transformer. The second primary winding 2 has a branch and is connected at one end to a third phase terminal (for example, A), and the second end is connected to a branch of the first primary winding 1. A third winding 3 is connected at one end to a grounded terminal (for example, X), and the second end connected to the branch of the winding 2. The secondary windings 4 are located on the same magnetic circuits 5 as the primary windings 1, 2 and 3. The connection diagrams of the primary 1, 2 and 3 and secondary 4 windings are the same. The branches from the primary and secondary windings divide these windings in the same proportion., The values of these proportions can vary depending on the requirements for the voltage values on the individual windings. If necessary, the transformer is equipped with a zero sequence filter.

The transformer operates as follows.

The primary voltage applied to the terminals of the transformer with a certain transformation coefficient is transmitted to the secondary windings 4. When the phase voltage of the network operating with an insulated neutral is symmetrical, between the zero-sequence capacitance of the network and the non-linear magnetization inductance of the grounded transformer, ferroresonance is no longer possible at the fundamental frequency. nor on a subharmonic. It is also impossible to damage the transformer during arc short circuits of the network to the ground, since the equivalent emf of the source acting in the circuit is sufficiently small.

The value of the equivalent EMF of the circuit is determined from the vector diagram of the mains voltage and the transformer windings. It is equal to the distance between the star center of the primary phase voltage of the network relative to the ground and the soldering potential from the second primary winding 2 of the transformer. In the symmetric mode of operation of the network, when the earth potential is in the center of gravity of the triangle of primary voltages, the value of the equivalent EMF depends

only on the branch potential of the winding 2, which in turn depends on the accepted proportions for dividing the turns of the windings by the branches. Using various proportions of dividing the turns of the windings by branches, even the complete absence of equivalent EMF can be achieved. This occurs if the branch of winding 1 is made in its middle, and the branch of winding 2 is two thirds of the phase output.

The small value of the equivalent EMF of the circuit, or even its complete absence, allows us not to take into account the addition of source energy to the circuit when the network capacitance is discharged through the voltage transformer. This makes stable ferroresonance impossible and reduces the requirements for the amount of loss necessary to ensure the transition of the vibrational discharge to aperiodic or close to it. Under these conditions, the probability of ignition of the grounding arc in one polarity, which can lead to damage to the transformer, drops sharply, and the reliability of the transformer increases. The proposed connection scheme wraps around the possibility of expanding the field of application of antiresonance voltage transformers of increased reliability, which are resistant both to arc short circuits to earth and to ferroresonance.

Claims (2)

1. A three-phase voltage transformer containing three primary windings, the ends of which are connected to three phase terminals intended for connection to three phases of the network and to one grounding terminal, the ends of the first primary winding are connected to the first and second phase terminals, one end of the second winding connected to the third phase terminal, one end of the third winding is connected to the grounded terminal, and secondary windings, the connection circuit of which repeats the connection circuit of the primary windings, wherein, for the purpose of lowering tim material-first and second primary windings have a branch, a second end of the second coil connected to the branch of the first coil, the second end of the third winding is connected to the branch of the second coil. 2. The transformer according to claim 1, characterized in that the branch of the first primary winding is made from the middle of its turns, and the branch of the second primary winding is made from two-thirds of its turns, counting from the phase output.