SU920576A1 - Device for non-damaged phase selection - Google Patents

Description

I

This invention relates to electrical fission measurement technology and may be. Used in determining the location of Ofi-phase earth faults in overhead power lines with MSOJttipO bath neutral. . .

- A device for multiphase short circuits containing resistance relays, a logic element (mini selector or max selector) for comparing absolute values, for example, voltages in two or more phases 1}, is known.

The disadvantage of the device is its complexity in the case of single-phase earth faults. :

Closest to the proposed by. a technical entity is a device that implements a method of forcing a ground fault to one of the intact phases and fixing the parameters of an artificial two-phase short circuit. Device for automatic election

The voltage to be connected to earth contains a voltage transformer, to the secondary winding of which three threshold elements are connected, each of which is connected between one of the phases and the zero output and controls the voltage between the phase and the ground 2.

A disadvantage of this device is its low sensitivity at

10 is the closure of the power line to earth through a large transition resistance when the voltage of the closed phase is not zero.

The aim of the invention is to increase the sensitivity when a transmission line is shorted to ground through a large contact resistance.

This goal is achieved by the fact that a logic switch (mini-selector) and a comparison block are connected to a device for electing a disconnected phase containing a voltage transformer connected to a monitored line, a two-position switch whose input is connected to the output of the control unit with two phases and a zero output of the secondary winding of a voltage transformer, the third phase and the zero output of which are connected to the first input of the comparison unit, the second input of which is connected to Exit logic element, and an output unit connected to the comparison input of the switch-off control unit.

Fig. 1 shows the protection scheme for determining single-phase closures, land-to-earth in air lines with an insulated neutral and with a device for electing an intact phase; FIG. 2 is an example of implementation of a logic element and a comparison unit;

The device contains a monitored line 1, a transformer 2 voltage, two connectors 3 and a control unit 5 and 6, a two-position switch 7 with a control unit 8, an operating current source 9, a logic element 10, a comparison unit P, a matching transformer 12 rectifiers 13. diodes I, resistors t5, transistor 16.

The device works as follows.

If any phase 1 line to ground is generated, the device must select one of the intact phases and connect it to ground via short circuit 3 or C. If, for example, phase C is shorted to earth, short-circuit A should be turned on. If phase A or B is shorted to ground, short-circuit 3 must turn on. This creates an artificial short circuit, the parameters of which, and hence the distance to the damage, are fixed by a special a device (not shown),

The logic element 10 (mini-selector) connected to the voltages of the two phases selects and passes the smallest of them to the output. This voltage is applied to one of the inputs of comparison unit 11, which is connected to the third phase by another input. Tat CTM, block 11, responds to the difference between the smallest voltage of phases A and C and the voltage of phase B,

If a phase A or C is shorted to earth, then a damaged phase voltage is supplied to comparison unit 11 and an intact phase B voltage is applied. If the fault occurs at phase 6, then the damaged phase voltage B and voltage arrive to comparison unit 11 Any of the intact phases A or C. Therefore, in any case, the inputs of the comparison unit 11 receive two signals, one of which is equal to the voltage of the damaged phase, and the other to the voltage of the intact phase. Comparison unit 11 responds to the difference in the applied voltages. Depending on the sign of the difference in the compared voltages, the comparator unit 11 either switches or not. If the difference difference between the compared voltages is positive, the comparison unit 11 is activated and sends a signal to the control unit 8, which switches the two-way switch 7- The latter prepares the short circuit switch Q via the control 6, when the negative difference difference sign is compared, the comparison block 11 does not work, therefore switch 7 through the control unit 5 prepares the inclusion of a short-circuit switch 3- After this, the source 9 of the operational one is switched on, which includes the prepared short-circuit ykatel 3 or y phase on intact.

Comparison unit 11 (Fig. 2) is made of a transistor 16, the base circuit of which includes two parallel diode-resistor circuits 1415, which are part of the logic element 10. The voltage from the secondary winding of the transformer 2 is supplied to the diode-resistor circuits and transistor 16 through matching transformers 12 and rectifiers 13. In the collector circuit of transistor 16, the input of control unit 8 is controlled by a two-way switch 7. If both UQO and Ufo signals are larger than Ujo, then transistor 1b is closed. If at least one of the UQO signals or less of the Ufte transistor; 16 opens, the control unit 8 is energized, which switches the switch 7, the proposed device allows you to automate the process of electing the phase that you want to close

ground and, thereby, accelerate the detection of damage to the line.

Claims (2)

1. Fedoseev A.M. Relena protection of electrical systems. M., Energie, 1976, p. . 2. Pekler V.N. Determination of short-circuit locations in air networks with insulated neutral. Industrial energy, 1973f № 5 (according to the type). / I B c