SU851608A1 - Device for protecting three-phase electric installation from incomplete-phase modes - Google Patents

Description

(54) DEVICE FOR PROTECTION OF THREE-PHASE

ELECTRICAL INSTALLATIONS FROM FULL-PHASE MODES

one

This invention relates to electrical engineering, in particular, to relay protection devices.

It is known a device for three-phase electrical installations from non-full-phase modes, comprising a three-phase half-wave rectifier connected to controlled phases. The rectifier output is connected to the thyristor anode and power button, with the last second end connected to the thyristor control electrode. Regulator ij is connected between the cathode and the network zero point.

The disadvantage of this device is limited functional capabilities, i.e. the device does not respond to incomplete-phase modes of the three-phase network with the motor nature of the load. In this case, if one of the line wires of the power supply network is broken (or accidentally disconnected), the voltage in this phase of the motor does not disappear, but only decreases - a considerable voltage develops on the motor winding in this mode. This voltage increases even more with the rotation of the rotor motor in a single phase mode.

due to geyeration of this phase by an additional electromotive force. Consequently, at the input terminals of the device, the voltage does not completely disappear, and the device does not functionally provide detection of a non-polyphase mode. In addition, the need to use a thyristor with a higher value of the maximum permissible direct voltage due to its connection through a rectifying bridge to the full phase voltage of the network and a possible fast failure of the thyristor, as well as

15 and the device as a whole, due to the absence of a limiting resistor in its control circuit.

Closest to the offer20. A device for monitoring the presence of voltage in the phases, containing a three-phase half-wave rectifier connected to the monitored phases. The output of the rectifier 25 mitel is connected to the thyristor anode and, through series-connected resistor and start button, to the control electrode of the thyristor. Between the zero point of the network and the cathode of the thyristor is included executive body.

thirty

If a three-phase system is present at input zykims, it is energized by its voltage at the thyristor anode during the whole period that a positive voltage, rectified by a three-phase half-wave rectification, is applied. If at the same time a short contact of the start button is closed, then the thyristor will open, the executive authority will give a signal corresponding to the presence of voltage on the nuts (or a signal to switch on the loading). The circuit goes into a steady state, maintained when the start button is opened (the thyristor is held in the open state by the current flowing through it).

With the complete disappearance of one of the phases of the voltage being monitored, the output of the rectifier-bridge does not have a positive waveguide of this phase. For 60 the voltage at the anode of the thyristor is zero, the current through it decreases to zero. The thyristor is locked and, due to the absence of control voltage, it remains in this state and in the positive half-periods of the intact phases of the mains supply. The thyristor rupture of the power supply circuit of the executive body provides the last signaling of the disappearance of the phase of the supply voltage (or disconnection of the load) 2.

The disadvantage of this device is its limited functionality - the device does not respond to the disappearance of the voltage of one of the mains phases during the motor nature of the load (due to the presence of voltage on the line wire damaged by the mains supply). Consequently, the known device is not able to control the shortness {apr of the phases of the motor load. In addition, it is necessary to use a thyristor with a higher value of the maximum permissible direct voltage due to its inclusion through a rectifying bridge to the full phase voltage of the network.

The purpose of the invention is to control the presence of voltage phases of a motor load.

The goal is achieved by the fact that the device for protection of a three-phase electrical installation from non-full-phase modes, containing a thyristor, whose control network includes serially connected start buttons and a limiting resistor, and an actuator connected between the thyristor cathode and the zero point of the network, are additionally introduced resistor dividers voltage by the number of phases, connected via diodes to the phases of the network, and dynistors, connected by anodes to the outputs of the mentioned

dividers, and cathodes - to the thyristor anode and the limiting resistor of the thyristor control circuit.

Figure 1 shows the electrical circuit of the device proposed; figure 2 - diagram of instantaneous values on the anodes of dynistor.

A device for three-phase electrical installation from non-full-phase modes contains semiconductor diodes 1-3, resistor voltage parts formed by pairs of resistors 4 and 5, 6 and 7, 8 and 9 connected via diodes 1-3 to the controlled phases of network A, B and C (Fig.). Dynistors 10–12 are connected to the output divider of the anode divider. The cathodes of the latter are connected to the anode of the thyristor 13 and the limiting resistor 14 connected in series with the start button 15 to the circuit of the control electrode of the thyristor 13 Between the neutral wire of the network and the cathode of the thyristor, the actuator 16 of the device is connected.

In Fig. 2, the following designations are used: 17, 18, 19 — voltage variation curves at the dynistor anodes (10, 11, and 12, respectively) in normal operation, 20 curves of the voltage variation at the distor 10 anode in the incomplete phase mode (with a motor load ), 21 — curve of voltage variation at the anode of the dynistor 10 in an incomplete phase mode (with a motor load, to a greater extent, its load); U is the voltage including my t,

not dynistor; t, t.

dynistor turn-ons (10, 11, and 12, respectively) in normal operation; - the moment when the dynistor 10 is turned on in an incomplete phase operation mode; t, is the time instant of the end of the positive half period of the voltage of phase C.

In normal operation, terminals A, B, and C of the monitored network operate a three-phase symmetrical voltage system. The positive half-waves of this system | through the diodes 1-3 are applied to resistor voltage dividers 4 and 5, 6 and 7, 8 and 9. The diagram of the instantaneous values at the outputs of the dividers is shown in Fig. 2. At time t, the voltage of phase A reaches the switching voltage of the dynistor 10 - Up. However, the start button 15 is open, the thyristor 13 is closed and, consequently, the current through the dinistor 10 does not flow. The dynistors 11 and 12 are in a similar state. The executive body 16 of the device is thus de-energized, which corresponds to the disconnected state of the aluminum receiver.

Claims (2)

When the circuit is started (short-circuiting the button 15), the dynistor 10 is turned on at time t, a positive voltage is given to the control electrode of the thyristor, it is unlocked, providing power to the actuator 16 and turning on the protected electrical receiver. Button 15 can now be open. The dynistor 10 and the thyristor 13, by the action of the current flowing through them, remain open. The variable resistors 4,8 and 6 of the voltage at the outputs of the dividers are chosen so that the inclusion of each subsequent dynistor (for example, dynistor 11 at time t2) occurs in the positive half-wave of the pre-dynistor voltage. By fulfilling the latter condition, continuous flow of current through the thyristor, t; e, is achieved. its open state is in normal operation, the requirement to provide the described operation mode of the dynors (whose switching voltage UB does not exceed 150 V) on the device as a whole. Conditiones the use of resistor voltage dividers connected at the outputs of single-phase half-wave rectifiers in the circuit. With the disappearance of one of the phases of the nutritional voltage (for example, phase A) and the motor nature of the load, the voltage of this phase decreases slightly. When the phase voltage decreases to the value shown by curve 20 (Fig. 2), the switch on of the 10 occurs at the time t after the voltage of the previous phase (C) decreases to zero (tp). In the time interval to the voltage on the anode of the thyristor is absent, and consequently, the current does not flow through it. The thyristor is closed with and remains in this state (due to the absence of control voltage) and when voltage appears on its anode at time t . The thyristor breaks the power circuit of the executive organ ensures the disconnection of the protected electrical receiver, in particular, the electric motor. With a deeper decrease in the voltage of phase A of the electric motor in the non-phase mode (curve 21 of Fig. 2), the switching of the dynistor 10 does not occur. The absence of voltage at the anode of the dynistor in the Internet causes it to lock. The actuator 16 is de-energized by disconnecting the protected motor. Under static load, the voltage of the damaged phase decreases to zero. Similar to the case discussed above, in the interval, there is no voltage at the anode of the thyristor, and the device operates as described above. The positive effect provided by the new set of features is the expansion of functionality. device capabilities. By introducing threshold elements (dynors 10–12), the device is sensitive to incomplete-phase modes, not only static loads, but also motor ones. In addition, the use of resistor voltage dividers reduces the limit value of the voltage on the thyristor and, therefore, reduces the increased requirements for its maximum allowable forward voltage. Claims of the Invention A device for three-phase electrical installations from non-full-phase modes, comprising a thyristor, in the control circuit of which there are serially connected start buttons and a limiting resistor, and an actuator connected between the thyristor cathode and the zero point of the network, characterized in that the presence of voltage phases of the motor load; resistor voltage dividers by the number of phases, connected via diodes to the phases of the network, and dynistors connected nodes to the outputs of said dividers, and the cathode - to the anode of the thyristor and a current limiting resistor circuit controlled; laziness thyristor. Sources of information taken into account in the examination 1. The author's certificate of the USSR 639077, chl. H 02 H 7/08, 1979. 2. Authors certificate of the USSR 597973, cl. G 01 R 19/00, 1978. 20 13 nineteen