SU1495895A1 - Device for damage protection of three-phase motor - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection devices, and is intended for the protective disconnection of a three-phase electric motor during emergency operation. The purpose of the invention is to expand the functionality of the device. The signal from the output of current sensor 1 is rectified using diodes 2 and 3 and is applied to executive relays 4-6. The overload relay 4 is activated when the motor current exceeds the permissible value. The minimum current relay 5 is activated when the motor current decreases to a value close to the no-load current. Relay 6 is designed to prevent operation when relay 4 is overloaded when the engine is started. Using potentiometers 11 and 12, reset buttons 7 and 27, and a circuit with indicator light 26, you can perform a simplified calibration of the protection settings during normal operation of the motor. 1 zpf.1 ill.

Description

The invention relates to the field of electrical engineering, in particular to relay protection devices, and is intended for the protective shutdown of a three-phase electric motor during emergency operation (overload, short circuit, phase failure, and also with unacceptable lowering; supply voltages and currents).

The purpose of the invention is the expansion of the functionality of the device.

The drawing shows a schematic diagram of the proposed device.

The device contains a current sensor 1 included in the circuit of one of the network phases, rectifier diodes 2 and 3, connected one in parallel and the other in series with the current sensor 1, overload relay 4 and the first 5 and second 6 undercurrent relays. Relay 4 winding through opening button 7 Reset and opening contact 8 of relay 6 is connected to one of the terminals of the current sensor 1, and relay windings 5 and 6 through respectively opening contact 9 of the overload relay 4 and the first opening contact 10 of relay 5 are connected to the same output of the sensor 1 current, while the other inputs of the relay 4-6 through potentiometers 11-13 are connected to another ⁵ * output. Of the current sensor 1 through a rectifier • diode 3, with windings 5 and 6 and po; Connected with them ^ potentiometers 11-13 are shunted by capacitors 14 and 15s

The first 17 and second 18 contacts of the Start button and pin 19 of the Stop button are sequentially connected to the winding circuit of the magnetic starter 16. In parallel with the first contact 17 of the Start button, the make contact 2ΰ of the magnetic starter 16 is connected, and the make contact 21 of the relay and contact 22 of the device operation mode switch are connected in parallel with the second contact 18. A circuit from a series-connected third diode 23, a second NC contact 24? the relay 5, the current-limiting resistor 25 and the indicator lamp 26 has terminals for connecting between one of the phases of the supply network and the neutral wire. End button 27 Reset is connected in parallel with potentiometer 12.

Instead of plugs 28 and 29 when not. Accurate calibration of the device requires measuring instruments (milliammeters).

The power contacts 30 of the magnetic starter 16 are included in the phases of the supply motor 31 of the network.

The device operates as follows.

In the initial state, the motor 31 is turned off. There are no currents in the linear wires A, B, C, there is no voltage at the output of the current sensor 1 (on capacitors 14 and 15), the relay

4-6 are disabled. The control circuit of the magnetic starter 16 is prepared for start-up. Relay 4 is set to a current value that exceeds the permissible load current of the power receiver. Relays 5 and 6 are set to the value of the no-load current of the power receiver. The setpoint for relay 6 is less than the setpoint for relay 5.

Start.

When the Start button is pressed, * contacts 17 and 18 are closed, while the magnetic starter 16 is activated and its contacts 30 are closed, current flows through the linear wires A, B, C. At the output of the current sensor 1 (on capacitors 14 and 15), a voltage appears that energizes the actuator - relay 4-6. To prevent the device from tripping at the moment of inrush current inrush, relay 6 is the first to activate and by pin 8 it opens the power supply circuit of relay 4 winding (overload relay). Then, relay 5 is turned on and by contact 10 it turns off the power supply circuit of relay 6. With a time delay determined by the discharge time constant of the capacitor 15 (of the order of 5-10 s), relay 6 is turned off, and then its contact 8 closes.

i

Stationary mode.

The load current is normal. The current value set by potentiometer 11 of relay 1 is less than the current of its operation and relay 4 is in the off state, and the current value set by potentiometer 12 of relay 5 exceeds its setting and relay 5 is turned on. Relay 6 is disconnected by pin 10 of relay 5.

Invalid motor overload mode.

In all phases A, B, C of the network, the current increases, at the output of the current sensor 1 (on capacitor 14), the voltage increases. In this case, the current through the coil of relay 4 exceeds the response current of the relay. Relay 4 is turned on and by contact 9 it turns off the power supply circuit of relay 5. Relay 5 is turned off with a time delay determined by the discharge time constant of capacitor 14, after which contact 21 of relay 5 in the circuit of magnetic starter 16 opens. At the same time, contacts 30 of magnetic starter 16 and motor 31 open disconnects from the network.

Inadmissible motor current reduction mode.

This mode is dangerous, for example, for a submersible electric motor, where pumped water (or oil) is used to cool the electric motor and lubricate the sliding bearings. The electric motor is quickly damaged if there is no or reduced water flow in its internal cavities.

Protection works as follows.

With an unacceptable decrease in the current of the electric motor 31, the current through the current sensor 1 decreases, respectively, the voltage across the capacitor decreases

14 .. The current through relay 5 becomes less than its setting value and relay 5 is turned off. This opens the contact 21 of the relay 5 in the circuit of the magnetic starter 16 and the motor 31 is disconnected from the network.

Similarly, the device works in the event of phase breaks, as well as with an unacceptable undervoltage in the supply network.

The proposed device uses cheap small-sized and miniature DC relays, for example RES-22, which have a return coefficient K _in = 0.2-0.3. Therefore, the calibration of the proposed protection device by known methods is not recommended. In this connection, it is necessary to calibrate the protection settings in the proposed device as follows.

I

The motor 31 is turned on. The currents in all phases are the same and equal to the nominal. The contacts 22 of the switch of the operating mode of the protection device are closed (calibration - protection). Resistance potentiometers 11 and 12 are initially set to maximum. In this case, the overload relay 4 is in an idle state, and the minimum current relay 5 is in the tripped state (its anchor is released). Contact 24 of relay 5 is closed and indicator lamp 26 is on.

First, relay 5 is calibrated, which is configured to lower the load current, i.e. Relay 5 should turn off the electric motor when its load current decreases to the idle current of that stroke. In this case, the potentiometer slowly and smoothly decreases its resistance, alternately pressing the Reset button 27 ”. This is done in order to force 15 to turn on relay 5, i.e. not at its full current Icp.p, ^{but P} R ^I (0.7-0.8) 1 srr

Pressing the button 27 to reset the circuit resistance 12 and now through its winding prote20 repents current equal to (0.7-0.8) _Example 1, but the relay 5 remains activated / If the load current relay winding electroreceivers introduced drop by 50-60 %, relay 5 will turn off the electric motor, as “respectively, the response current of the relay decreases to (0.2-0.3), where (0.2-0 ', 3) the return current of relay 5.

When calibrating relay 4 to increase the load current above the permissible ed, potentiometer 11 first decreases its resistance until relay 4 turns on and contacts 9 disconnect relay 5, while contact 24 of relay 5 closes ₍ and indicator lamp 26 lights up. Then, slowly and smoothly increasing the resistance of the potentiometer 11 and alternately pressing the Reset button 7, make sure that the Indicator lamp 26 goes out, that is, relay 4 is turned off and relay 5 is turned on accordingly. By opening contact 7, they make relay 4 turn off s nothing to do with the return ratio (0.2-0.3), and at (0.7-0.8) 1 _^?, ie 4 relay work when the load current exceeds the power-consuming equipment by 20-30%..

A more accurate calibration of protection for critical motors is carried out according to the readings. devices (milliammeters) that are included instead of plugs 28 and 29 in relay circuit 4 and 5.

Thus, by introducing two undercurrent relays, the device’s functionality is expanded by providing protection in idle modes,

14 ^ 5895 phase breaks, as well as an unacceptable decrease in the supply voltage level. By introducing a circuit with an indicator lamp and Reset buttons in the measuring relay circuits, it is possible to simplify the calibration of protection settings during normal operation of the electric motor.

Claims (1)

Form of invention Device for protecting three-phase electric motor from damage I 1 nd ny, containing a current sensor of the first of the phases of the electric motor, a first diode, a shunting output of the current sensor, an overload relay with a potentiometer in its winding circuit and a magnetic starter, the power contacts of which have terminals for connecting to the mains motor, magnetic starter jacket through the first and second contacts of the Start button and the Stop button contact connected between the second and third phases of the supply network, the first contact of the P button It is connected with the closing contact of the magnetic starter, and more often, for the purpose of disorder, they are additionally introduced, while the first conclusions are made by the shielding of functionality in the first and second relays of the minimum tube and the current of the mentioned overload relay and the first and second relay of the minimum current are connected to the ^ node of the first diode through the opening contacts of the second undercurrent relay, the overload relay and the first opening contact of the first undercurrent relay, respectively, the second terminals of the relay windings each through s second potentiometer connected to the cathode of the second diode inputted newly, kotoro10 anode coupled to the second. cathode of the first diode, while the windings of the first and second undercurrent relays with potentiometers are shunted by the first and second respectively newly introduced capacitors, the make contact of the first undercurrent relay is connected in parallel with the second contact of the Start button. 20 2. The device according to p. Characterized in that, in order to simplify the process of calibrating the protection settings, an additional circuit of 25 third diodes, a second contact of the first undercurrent relay, a current-limiting resistor, and an indicator lamp having terminals for connecting between one out of phase 30 of the supply network and the neutral wire, the contact of the device operation mode switch, connected in parallel with the second-contact of the Start button, and the opening and closing buttons of the Reset button, respectively switched on 35 to the winding circuit of the overload relay and parallel to the potentiometer in the winding circuit of the first undercurrent relay.