SU811391A1 - Device for protecting three-phase electric motor from incomplete phase mode - Google Patents

Description

The invention relates to electrical engineering, in particular, to devices for the relay protection of electric motors from an incomplete phase mode.

A device for protection of a three-phase electric motor is known, which contains a thyristor, the electrodes of which are connected to the phases of a three-phase network, and at the anode value a direct current relay shunted by a capacitor is turned on. However, the shutdown of an electric motor in the incomplete phase mode by a known device is possible only in the intermittent mode of operation of the protected motor.

It is also known a device (2) containing a three-phase rectifier, to the output of which the thyristor anode is connected, and through the resistor and self-return button connected in series to the control electrode of the thyristor, the cathode of which is connected to one of the conclusions of the executive body.

However, when the voltage is generated in the incomplete-phase mode, the "lost phase" of the electric motor will flow a current through the thyristor, keeping it open. The operation of the device in this case is impossible.

The loss of one of the phases of the supply voltage often occurs due to contact failure at the point where the line is connected to the switching device, contact of the switching device itself, as well as the fuse insert fuse in one of the phases.

The known device does not respond to the listed types of damage associated with switching and protective devices of the electric receiver, since its sensor, three-phase rectifier are connected to the specified devices.

The aim of the invention is to increase the sensitivity of protection against incomplete-phase modes and enhancement of functionality.

Claims (1)

To do this, a device for protection of a three-phase electric motor against an incomplete-phase mode, comprising a motor start button, a resistor and a three-phase half-wave rectifier, the output of which is connected in series with a thyristor, a limiting resistor and an actuator coil, additionally equipped with an artificial switching circuit of the thyristor, a diode and a second three-phase actuator element, a diode and a second three-phase control element, with a headset, a three-phase, three-phase, one phase, three-phase, one phase, and one actuator coaxial, and a second three-phase control element, a diode and a second three-phase actuator, an arrays, a diode and a second three-phase actuator the rectifier, at the output of which the start button of the electric motor is turned on, is connected to the second end the diode anode and resistor, the other ends of which are connected respectively to the anode and the adjusting electrode of the thyristor, the first of the mentioned three-phase single-wave rectifiers connected directly to the terminals of the electric motor, the second to the three-phase supply voltage system, and the circuit of the artificial switching of the thyristor, the of a series-connected capacitor and resistor, connected in parallel with the said limiting resistor and the actuator coil, the other end of which connected to the neutral point of the network. FIG. 1 shows a functional diagram of the device. The device contains a normally open contact I relay, coil 2 contactor, three-phase half-wave rectifier 3, normally open contact 4 of the motor starting button, diode 5, semiconductor, resistor 6, contacts 7 of contactor 2, resistor 8, relay coil 9, normally closed contact 10 motor stop buttons, thyristor 11, three-phase half-wave rectifier 12, resistor 13, capacitor 14, electric motor 15, terminals A, B, C of a three-phase sinusoidal alternating voltage. FIG. Figure 2 shows the diagram of the rectified voltage supplied to the thyristor anode 11, corresponds (Fig. 2, a) to the normal mode of operation of a three-phase electric motor, when a three-phase symmetric voltage is applied to its terminals, corresponds (Fig. 2, b) to the case of disappearance of one from the phases (e.g., phase A) of the supply voltage. The device works as follows. If there is a symmetric star for the supply voltage, the waveform at the output of the rectifier 3 has the form shown in FIG. 2, a. When the motor start button 4 is closed, the voltage taken from the rectifier 3 is supplied through diode 5 to the anode and through the resistor 6 (limiting thyristor control current to an acceptable value) - to the control electrode of the thyristor 11. The thyristor opens, the capacitor is charged 14 of the artificial switching circuit, and along the chain: a resistor 8, a normally closed contact 10, the winding of the relay 9 flows a rectified current. Relay 9 is activated and closes with its contact 1 the supply circuit of the coil 2 of the contactor. The contactor, in turn, switches the power supply circuit of the electric motor 15 by terminals 7. The electric motor starts. Simultaneously with the start of the electric motor, the voltage is applied to rectifier 12. Obviously, the shape of the voltage produced by rectifier 12 will have the same appearance as the output voltage of rectifier 3 (Fig. 2, a). The rectified voltage is applied to the anode of the thyristor 11. When selecting the response current setting of relay 9, the higher thyristor holding current, the positive potential is removed from the control electrode by releasing the motor start button 4 does not lock the thyristor and the winding of the relay 9 flows around the current. Diode 5 prevents the supply of positive voltage, rectified by rectifier 12, to the control electrode of thyristor 11. When one of the phases of the supply voltage disappears, the rectified voltage decreases to zero in the time interval 60 el. hail. (Fig. 2.6). The thyristor 11 is closed, the relay 9 releases its contact 1 and the coil 2 of the contactor, opens its contacts 7, disconnects the electric motor from the network. With the passage of time interval of 60 e. hail, in case of a delay in opening the contacts 7, the voltage rectified from phases B and C is applied (when phase A disappears) to the thyristor anode I, but the latter remains in the closed state, since there is no current in its control electrode circuit. An artificial switching circuit of a thyristor consisting of a series-connected resistor 13 and a capacitor 14 is provided in a circuit for increasing the sensitivity of the protection. The motor is stopped for a short time by a button 10 on the current in the circuit of thyristor 11. At the same time, the thyristor is closed, the relay 9 by its contact 1 de-energizes the coil of contactor 2, which by contacts 7 turns off the motor. The positive effect is to increase the sensitivity and reliability of the protection of electric motors from non-phase modes, as well as the versatility, which consists in the fact that the proposed device is suitable for protecting electric motors of any power. Apparatus of the Invention A device for protection of a three-phase electric motor against an incomplete-phase mode, comprising an electric key start button, a resistor and a three-phase single-cycle rectifier, at the output of which a series-connected thyristor is connected, the limiting resistor of the actuator element, which, in order to increase sensitivity and expand, is necessary to increase the resistance of the actuator element, so that, in order to increase sensitivity and expand, the coils of the actuating element, which, in order to increase sensitivity and expand, are required to increase the level of the actuator element, in order to increase sensitivity and expand, , additionally equipped with a thyristor ommutation circuit, a diode and a second