RU21700U1 - DEVICE FOR PROTECTING A THREE-PHASE ELECTRIC MOTOR AGAINST PHASE - Google Patents

Description

DEVICE FOR PROTECTING A THREE-PHASE ELECTRIC MOTOR AGAINST PHASE

The utility model relates to electric motor protection devices and can be used for signaling about non-phase modes of operation of three-phase electric motors caused by blown fuses or phase conductors, or for automatic switching of electric motors from the mains supply in the event of such modes.

Known devices for protection of three-phase electric motors from phase reversal. An example of such devices can be a device that responds to fuse blowout i, s316, Fig. 14.3, a device that responds to the disappearance of current in one of phases 1, p. 316, Fig. 14.3.6, a device that responds to the neutral displacement of the stator winding of the electric motor when the phase t is timbered, p.316, Fig. 143 c, a device that responds to a symmetry breaking 1 | of the phase voltage system at the motor terminals and uses the principle of creating an artificial zero point 2 , p., fig. 3.

These devices have the following disadvantages: the first of them does not provide protection if the asymmetric mode is caused not by a blown fuse, but by another reason, the second requires the installation of high-current relays and a large number of relay equipment, for

MPK4N02N7 / 09

of the third, it is necessary to have a neutral neutral point of the stator winding of the electric motor, and to perform the fourth device, capacitors of significant capacity are required, which affects the dimensions and cost of the protection device. In addition, having high sensitivity, such a device can sometimes turn off the electric motor as a result of breaking electrical symmetry caused by asymmetric short circuits in the supply network.

Closest to the claimed device is a circuit device for protecting a three-phase electric motor from operating in two phases according to the certificate for useful model N 15620, containing three identical capacitors, the first and second current-isolating resistors, the first and second rectifier bridges, an RC circuit including a resistor and a capacitor , thyristor oshron and electromechanical relay 3.

This ushroyshvo devoid of the above disadvantages. However, it is not applicable; three-phase electric motors, the switching of the power circuits of which is carried out in two phases. These include electric motors of mechanisms of various cranes 4, p. 153, fig. 81, elevators and lifts 5, p. 122, fig. 94, for which reverse work patterns are characteristic. When the switched-off state of their switching devices (contactors, controllers, command devices) is saved

.

power supply of electric motors in one phase, which causes a false action of the protection device.

The utility model 5 seeks to expand the scope of the device by eliminating its false operation when the three-phase electric motor is disconnected from the mains by switching devices in two-phase phases while maintaining power in one phase. As a result of this, the device can be used to protect electric motors, in which the switching of power circuits is carried out both in three and in two phases.

The usefulness of the utility model is as follows. The drawing shows a diagram of a device for Zh1shchita three-phase electric motor from phase reversal. The diagram shows the closing contacts of switching devices of direct 1 and reverse 2 directions of rotation of the electric motor, included in the extreme and middle phases. The protection device contains three identical capacitors 3, the first 4i and the second 42 current-limiting resistors, the first 5i and the second 52 rectifier bridges, an RC circuit 6 containing a resistor 7 and a capacitor 8 connected in series, the first thyristor switch 9, an electromechanical relay 10, the first series a chain 11 of a rectifier diode 12, a current-limiting resistor 13 and a radiating part of a second thyristor optocoupler 14i, a second series circuit of a rectifier diode 16, a current-limiting resistor 17 and an emitting h parts of the third thyristor optocoupler 18i and the shunting chain 19 formed by successively connected receiving parts of the second 142 and third ISi thyristor ochrons. The first plates of the capacitors 3 are connected to the phase terminals of the motor windings, and the second plates are interconnected. The connection point of the second casing of the capacitors 3 through the first current-limiting resistor 4i and the inputs of the first rectifier bridge 5i is connected to the zero point of the motor power source. The diagonal of the first rectifier bridge 5i includes a series-connected resistor 7 and a capacitor 8 of the RC circuit 6, parallel to the capacitor 8 of which a shunt circuit 19 is connected and, through the second current-limiting resistor 42, the radiating part of the first 111 optocoupler 9. The receiving part of the first transistor optocoupler 9 is included in the diagonal of the second rectifier bridge 52, the inputs of which are connected to the poles of the AC source through the winding of the electromechanical relay 10. The input of the first series circuit 11, formed a the node of its rectifier diode 12 is connected to the connection point of the make contacts of switching devices of direct 1 and reverse 2 directions of rotation of the electric motor in the extreme phase from the side of the power source. The input of the second series circuit 15, formed by the anode of its rectifier diode 16, is connected to the connection point of the closing contacts of the switching devices of direct 1 and reverse 2 directions ///

singing rotation of the electric motor in the middle phase from the side of the power source. The outputs of the first 11 and second 15 consecutive circuits, interconnected, are connected to the connection point of the closing contacts of switching devices of direct 1 and reverse 2 directions of rotation in the middle phase from the side of the motor windings, and the closing contact of the electromechanical relay 10 is included in the signaling circuit about the phase failure.

The device operates as follows. In full-phase mode, the power supply to the motor windings does not have a potential difference between the connection point of the second capacitor plates 3 and the zero point of the motor power source. No current flows through the first current-limiting resistor 4i, the PFV rectifier 5i, the RC circuit 6 and the radiating part of the first thyristor optocoupler 9. The thyristor optocoupler 9 is closed, as a result of which current does not flow through the second rectifier bridge Za and the winding of the electromechanical relay 10. The closing contact of the electromechanical relay 10 in the signal circuit for phase failure is open.

When the power supply windings of the electric motor windings are out of phase and the contacts of the switching apparatus of the forward 1 or reverse 2 directions of rotation are closed, a potential difference appears between the connection point of the second capacitor plates 3 and the zero point of the motor power source. Current flows through the first current-limiting resistor 4t, the first rectifier bridge Si, the resistor 7, and the capacitor 8 of the RC circuit 6. After charging capacitor 8 to the output voltage of the first rectifier bridge 5i, it is discharged along the circuit formed by the second current-limiting resistor 42 and the radiating part of the first thyristor osron 9. The thyristor optocoupler 9 is unlocked, a second rectifier bridge Za is connected through its receiving part, and the winding of the electromechanical relay 10 from an alternating current source. The electromechanical relay 10 is activated, its contact is closed in the alarm circuit and a signal is given about the phase failure. With the current asymmetry of the voltage supplying electric motors, the device does not have time to operate due to the introduction of an RC circuit 6. The time required to charge the capacitor 8 introduces a delay into the slave of the protection device as a whole, providing the necessary detuning from short-term asymmetry caused by any reason.

The states of the first 11 and second 15 consecutive chains and the shunt chain 19 in these modes do not affect the behavior of the entire protection device. When the contacts of the switching apparatus of the direct 1 or reverse 2 directions of rotation of the electric motor are closed, the current flows continuously either only through the first 11, or only through the second 15 sequential chain, since the other of them turns out to be closed: 1911

switching device or connected to a de-energized phase. In this case, the receiving part of the corresponding thyristor oshron in the shunt chain 19 is closed, and the chain 19 is open.

With the open position of the contacts of switching devices of direct 1 and reverse 2 directions of rotation corresponding to the stopped state of the electric motor, its power is stored in one phase. A potential difference appears between the connection point of the second capacitor plates 3 and the zero point of the power source. Through the first current limiting resistor 4i, a first rectifier bridge 5i starts to flow. However, the capacitor 8 of the RC chain 6 and the radiating part of the first thyristor ochron 9 turn out to be shunted by the chain 19, since in this mode currents flow simultaneously along the first 11 and second 15 consecutive chains. The flow of currents along the radiating parts of the second 14i and third 18i thyristor oshrons causes the opening of their receiving parts, forming a shunt chain 19, and, therefore, leads to its closed state. Pfv thyristor oshron 9 is closed, as a result of which current does not flow through the second rectifier bridge 52 and the winding of the electromechanical relay 10. Its closing contact in the signal circuit for phase failure is open.

by using devices in dazh phases while maintaining its power in one of the phases, and the device is ensured operation during prolonged out-of-phase modes that occur when the switching devices are on.

If it is necessary to turn off the device, it is possible to use the opening contacts of the electromechanical relay 10 in the self-holding circuits of the windings of switching devices that supply power to the electrical installation of the mechanism in all three phases.

Laboratory tests of a prototype device for protecting three single electric motors from phase failure in the alumina workshop of the BAZ-SUAL branch made sure that the above properties of the utility model were present.

LITERATURE

1. Andreev V. A. Relay protection, automation and telemechanics in power supply systems. M .: Higher. school., 1985.

2. Protection of three-phase motors. , 1972, No. 8, p. 38-39.

3. Certificate for utility model of the Russian Federation No. 15620. Device for protecting a three-phase electric motor from working in two phases. Bull. Number 30.

4.Fotiev M.M. Electric drive and electric equipment of metallurgical shops. M .: Metallurgy, 1990.

Claims (1)

A device for protecting a three-phase motor from phase failure, containing three identical capacitors, the first plates of which are connected to the phase terminals of the motor windings, and the second plates are connected to each other and connected through the first current-limiting resistor and the inputs of the first rectifier bridge to the zero point of the motor power source, and in the diagonal of the first rectifier bridge includes a series-connected resistor and a capacitor of an RC circuit, parallel to the capacitor of which through the second an inducing resistor is included in the radiating part of the first thyristor optocoupler, and the receiving part of the first thyristor optocoupler is included in the diagonal of the second rectifier bridge, the inputs of which are connected to an alternating current source through the winding of the electromechanical relay, characterized in that the first series circuit of the rectifier diode is current-limiting resistor and radiating part of the second thyristor optocoupler, the second series circuit of a rectifier diode, current-limiting about the resistor and the radiating part of the third thyristor optocoupler and a shunt circuit containing series-connected receiving parts of the second and third thyristor optocouplers, while the input of the first serial circuit formed by the anode of its rectifier diode is connected to the connection point of the closing contacts of switching devices of the forward and reverse directions of rotation of the electric motor in the final phase from the side of the power source, the input of the second series circuit formed by the anode of its rectifier diode, is connected to the point of connection of the closing contacts of switching devices of direct and reverse rotation of the electric motor in the middle phase from the side of the power source, and the outputs of the first and second consecutive chains connected together are connected to the connection point of the closing contacts of switching devices of forward and reverse rotation in the middle phase with side of the motor windings, the shunt circuit is connected in parallel with the capacitor of the RC circuit, and the make contact of the electromechanical relay is connected to Ignalization of phase failure.