SU904074A1 - Device for determining damaged network phase - Google Patents

Description

(5M DEVICE TO DETERMINE DAMAGED NETWORK PHASE

I

The invention relates to electrical engineering, in particular, devices for controlling insulation during single-phase earth faults in networks with insulated neutral for use, for example, in conjunction with high-speed protection equipment against electric shock when a person accidentally touches any of the network phases. , voltage 1,1 - 10 kV.

Devices for determining the damaged phase are known, used in relay protection of electrical networks with insulated neutral, operating on the basis of a comparison of two voltages (currents) in phase or absolute value.

A device for determining (detector) of a faulty phase is known, which contains rectifiers and a DC amplifier, in the output circuit of which an actuating relay is connected.

The operation of this device is based on a comparison of the absolute value of two rectified currents caused by two phase voltages - reference and measuring. Diode on -. In accordance with the rectifier and opposite to the power source, it is an element comparing the reference current with the measuring current.

In the normal mode (in the absence of a single-phase ground fault), the condition

Uuim

Uo, or 1shchn 1o „D1)

ts

When one of the network phases (for example, phase A) closes to earth, the voltage between the phase and the earth at the damaged phase decreases (Fig. 2), and the meter decreases proportionally:

Claims (2)

20 current; upon reaching the value of; the measuring current is less than the reference current, the comparison diode is closed and the difference between the reference and measuring currents flows through the emitter-base transition of the amplifier, causing it to trigger 12. The disadvantage of this device is its low sensitivity due to the limitations on maintaining the (1) lagging (healthy) phase. From the vector diagram in FIG. 2 (point 0 ;,) it can be seen that at a certain ratio of the network phase capacitances relative to the earth and the earth fault resistance, condition (1) for the subsequent phase 8 is violated, i.e. UU, M CB) Uo (B) and their difference can lead to false positives at the subsequent phase 6. In order to avoid this, the sensitivity of the detector reacting to the specified difference of currents, which ultimately significantly limits the sensitivity of the device ea ki on earth. So, for example, when the capacitance of the phases of the network relative to the earth is 1 μF / phase, the sensitivity of this device will be no more than 1.5 kΩ / f ZU. Consequently, the sensitivity in the known device is limited by the condition that the actuator does not operate at a subsequent (healthy phase. The purpose of the invention is to increase the sensitivity and speed of the device for determining the damaged network phase. current by the number of phases in the output circuit, each of which includes an executive relay, the input of one rectifier is connected to the mains phase through The three-voltage splitting circuit, the other rectifier input is similar to the leading phase of the mentioned phase, and the outputs of the rectifiers are connected to the corresponding DC amplifier according to the comparison circuit of the two voltages in absolute value. by three voltages in front of each rectifier, it makes it possible to almost smoothly smooth the rectified input signal to the amplifier, which distinguishes it from the capacitive smoothing scheme with a significant delay triggered in a known device. FIG. 1 is a schematic diagram of a device for determining a faulty phase; in fig. 2 is a vector diagram explaining the principle of operation of the device (for the case of a single-phase closure in phase A). A device for determining the faulty phase (Fig. 1) includes rectifiers 1 and 2 (for example, three-phase Larionov), a DC amplifier 3 with an executive relay (for example, a reed switch or optocoupler) in the output circuit and D and 5 splittings into three phase-shifted voltages and functionally combined into block 6. Blocks 7 and 8 are similarly executed. Blocks 6.7 and 8 Are connected properly to the phases and 11 of the network. The device works as follows. In normal mode, the inputs of the rectifiers 1 and 2 of block 6 (for one of the phases 9 of the network) receive symmetrical voltages from the respective phases of the monitored network through the splitting circuits, which are rectified and compared with each other. When the phases of the network are symmetrical, the difference in the voltages of phases 9 and 11 is fed to the input of the amplifier 3 DC, i.e. Ug (.i 0, hf «) (i For blocks 7 and 8, respectively, of the two other phases 10 and 11, analogous differences equal to zero also come to the inputs of their amplifiers, since UBX (B) O and UBKCO O, - and 8 ( 10, in (c) (40) - c (11) With a single-phase earth fault (for example, phase A 9), the symmetry of the phase network voltages is violated and the input phase of the rectifier 2 receives the leading phase voltage LI (; (i) greater than the voltage of the damaged phase of the IAC that comes to the input of the rectifier 1. Then the positive difference of the voltages arrives at the input of the amplifier 3, the level is sufficient to open DC amplifier, in the output circuit of which the actuating relay operates. At the inputs of the respective amplifiers of the other two phases (in blocks 7 and 8 of figure 1), according to the expressions Ci) and (5), there are negative differences, because (the vector diagram of FIG. 2) while the triodes of the amplifiers are locked and the relays do not work on these phases.As can be seen from Fig. 2 (point 0), the sensitivity of the device according to the failure condition on the subsequent (healthy) phase is higher than in the known device. Thus, it becomes possible to determine the damaged phase by grounding through significantly but large resistances (with a network phase capacitance of 1 MFC / phase) up to 6 kΩ / phase. In addition, in the proposed device, in comparison with the known, the phase selection speed increases significantly. Since sensitivity and speed are the main safety parameters, the use of the proposed device for determining the damaged network phase as the main relay element in high-speed equipment for protecting people from electric shock significantly increases the level of electrical service safety. Apparatus of the Invention A device for determining a damaged phase of a network, comprising rectifiers, each of which is connected to a phase voltage, and DC amplifiers according to the number of phases, in the output circuit each of which an actuating relay is connected. increase sensitivity and fast action, the input of one rectifier is connected to the network phase through a three-voltage splitting scheme, the input of the other rectifier is similarly advanced to the network phase, and the outputs of these rectifiers are They are provided with an appropriate DC amplifier according to the scheme comparing two voltages with a magnitude absolute value. Sources of information taken into account during the examination 1. USSR author's certificate number 335763, cl. H 02 H 3/16, 1970. 2. USSR Author's Certificate If 531228, cl. H 02 H 5/12, 1973. ) VAX OhM-c-V tx (crV, -Uc 9 {fHfl) Vet