SU792353A1 - Device for shaping current at testing relay protection system - Google Patents

Description

The invention relates to the field of relay protection, namely to relay protection of power transformers and can be used for research and overlay differential protection with second harmonic current braking.

At present, various schemes for simulating inrush current fg magnetization are known, which are used to study the operation of the protection of the power transformer tU and Г2.

A common disadvantage of these circuits is the use of special transformers and the inability to control the shape of the simulated current within the required limits.

Closest to the proposed invention is a device for 20 forming a secondary current of a current transformer in a partial absorption mode of aperiodic component 3.

In such a device, it is variable and 25 the constant component in the generated secondary current regulates9 separately, but there is no possibility of controlling the percentage of the second harmonic and of the jQ

change the form of this current in a wide range.

The aim of the invention is to improve the shape of the current curve by adjusting the percentage of the second harmonic therein.

This goal is achieved by the fact that a device for forming a current when checking a relay protection, containing potentiometers, a transformer, a current, the primary winding of which is connected to two phases via a potentiometer and a rectifier to the linear voltage of the AC network, and the secondary is connected to a measuring device and the relay under test is equipped with a rectifying bridge and an autotransformer, and the current transformer is equipped with two additional windings, one of which is connected to the third through a potentiometer and rectifier bridge the phase and neutral of the network for phase voltage, and the other through the potentiometer, the measuring device and the autotransformer, to the three phases of the network.

Claims (3)

Fig. 1 shows a diagram of a device for forming a current when checking a relay protection in Fig. 2 a, b, c shows waveforms of currents in the device. The device {figure 1) contains a current transformer with windings 1,2,3 and 4. Winding 1 and 2 are connected respectively through rheostats 5 and 6, rectifiers 7 and 8, ammeters 9 and 10 to a three-phase network so that the rectifiers 7 and two voltages were applied with a mutual phase shift of 90 °. For example, if rectifier 7 is connected to phases C and C, rectifier 8 is connected to phase A and the neutral wire O. Winding 3 is connected in series with resistor 11 and ammeter 12 between the phase of the three-phase network and the moving contact of the autotransformer 13, which is connected to two other phases. When connecting 7 and 8 k straighteners. In these phases, the autotransformer 13 must be connected to phases A and B, and ammeter 12 to the phase;. Ammeter 14 and test relay 15 are sequentially connected to winding 4. The rectified currents shown in Fig. 2a come from rectifiers 7 and 8 through resistors 5 and 6 to windings 1 and 2, which create oppositely directed flows in the magnetic circuit. Therefore, in the winding 4 tra only the difference of the currents in the windings 2 and 1 is formed, which is a current ig (Fig. 2 a). This current has a frequency twice as large as the frequency of the network. The closest pole harmonic is only 8.6% relative to the second harmonic; therefore, the resulting current can be considered with sufficient accuracy as the second harmonic current. In the winding 3 a sinusoidal current flows with the frequency of the network, that is, the current of the first harmonic. The resultant current in winding 4 is determined by the sum of the currents of the first and second harmonics. The form of this current depends on the mutual shift in time of the first and second harmonics. For this purpose, the adjustment of the first harmonic phase is provided by means of an autotransformer. For example, at the top position I of the rheostat slider (Fig. 1), a current is formed in the winding 4, shown in Fig. 2b and corresponding to the periodic inrush of the magnetizing current. When the position is low And the rheostat slider in the winding 4, the current is generated, shown in Fig. 2c and corresponding to the transformed aperiodic inrush of the magnetizing current. The present invention is used in the research, development, and commissioning of relays of a power transformer, especially if they have a second-harmonic current braking. Claims An apparatus for generating a current when testing a relay protection, containing potentiometers, a current transformer whose primary winding is connected to two phases through a potentiometer and rectifier to an alternating current line voltage and which is secondary connected to the measuring device and the relay under test. so that, in order to improve the shape of the current curve by adjusting the percentage of the second harmonic in the current being formed, it is equipped with a rectifying bridge and an autotransformer, and The current regulator is equipped with two additional windings, one of which is connected to the third phase and neutral of the network for phase voltage through a potentiometer and a rectifying bridge, and the other through a potentiometer, measuring device and autotransformer to the three phases of the network. Sources of information taken into account in the examination 1. Drozdov A. D .. Electrical circuits with ferromagnetic cores in relay protection. M., Energie, 1974, p. 140. 2. Podgoniy S. D., Khlebnikov V. S. Modeling and calculations of transient regimes in chains of rulyuyenoy protection. M., Energie, 1974, p. 140. 3. Authors certificate of the USSR 493825, cl. H 01 And 47/00, 1968.