SU1234913A1 - Device for overload protection of electric motor - Google Patents

Abstract

The invention relates to electrical engineering and can be used to protect an electric motor against unloading in an automated electric drive of various mechanisms. The purpose of the invention is to improve the reliability and noise immunity of protection. The device contains a current transformer installed in one of the phases of the motor to be protected, the secondary winding of which is connected to a maximum current relay 21. The output relay (BP) 8 is double-wound with magnetic memory. When the engine is overloaded during operation, current is supplied to the primary winding of the BP 8. as a result, it opens its contact 7 and disables the catapult 3 starter. one . 2 z.i. f-ly, 2 ill. ((L of fig. 1 N

Description

The invention relates to electrical engineering and can be applied in an automated electric drive of various mechanisms.

The aim of the invention is to improve reliability, noise immunity.

FIG. 1 and 2 are diagrams for modifying the device.

The electric motor 1 is connected to the network through the contacts 2 of the actuator, the coil 3 of which is connected in series with the buttons Start 4, Stop 5. Parallel to the button Start 4 the circuit is made up of the contact starter 6 and the contact 7 of the output relay 8 with the magnetic one memory

The first winding of the output relay 8 through the disconnecting contact 9 of the Start button is connected in parallel to the resistor 10, a circuit consisting of a parallel-connected capacitor 11 and a resistor 12 is connected to one output. A second output winding of the output relay 8 is connected to the closing block contact 13 an actuator connected to the first output of the circuit connected in parallel between a capacitor 14 and a resistor 15. The second output of this circuit is connected via a resistor 16 to the output of a rectifier composed of diodes 17-19. The second output of the second winding of the output relay 8 is grounded (or connected to the second output of the rectifier).

The current transformer 20 is connected by the primary winding in series with the motor winding 1.

In the diagram shown in FIG. 1, the overcurrent relay 21 is connected to the secondary winding of the transformer 20, the closing contact 22 of which is connected between the output of the rectifier (diodes 17-19) and the resistor 23, which is connected to the capacitor 11 and the resistor 12. In FIG. 2 to the secondary winding of the current transformer 20 is connected to the rectifying bridge 24, the output of which is connected to the resistor 25 and the capacitor 26. The cathode output of the rectifying bridge 24 is also connected to the cathode of the zener diode 27, the anode of which is connected to the capacitor 11 and resistor 12. The anode output of the rectifier melee bridge 24 is connected to the second output of the first winding of the output relay 8.

The device works as follows.

When the engine is started, the button 4 is pressed. The start-up, the coil 3 of the actuator is activated, the engine 1 is connected to the network 2, and the closing contact 6 activates the switch 3 of the actuator to hold it. In this case, the disconnecting contact 9 of the Start 4 button, the first winding of the output relay 8, is disconnected from the circuit of the capacitor P. At start-up, a starting current surge is created.

In the circuit shown in FIG. 1, the overcurrent relay 21 is activated, closing its contact 22 and the supply voltage to the capacitor 11 from the rectifier - diodes 17-19. The capacitor is charged to the amplitude of the rectifier voltage and when the button 4 is released. Starting contact 9 closes, but the output power supply relay 8 does not receive from this circuit, since the capacitor 11 is charged.

In the diagram shown in FIG. 2, the inrush current on the resistor 25 produces a voltage greater than the breakdown voltage of the Zener diode 27. The capacitor 11 is charged through the resistor 10, but this voltage does not go to the output relay 8 because contact 9 is open. In both schemes, when the coil 3 of the actuator is turned on, contact 13 closes, which through capacitor 14 generates a current pulse in the second winding of output relay 8. This sets output relay 8 to the position at which its contact 7 closes.

After starting in the circuit in FIG. 1, the overcurrent relay 21 drops off and opens the contact 22. In both schemes, the capacitor 11 is discharged through the resistor 12 and is thus prepared to pass the current to the first winding of the output relay 8.

If an overload occurs in the engine operating mode, this will cause current output 8 to flow into the first winding, as a result of which it opens its contact 7 and disconnects the coil 3 of the actuator and, therefore, the motor from the network. In the circuit shown in FIG. 1, this is due to the fact that when overloaded, the overcurrent relay 21 will operate and close its contact 22 by connecting the first winding of the output relay 8 through a resistor

23and a capacitor and a rectifier. In the diagram of FIG. 2 connect first

0 winding of the output relay 8 to the nanowire

24 is caused by a high voltage at its output, which exceeds the threshold of the zener diode 27.

The proposed device consists of standard elements having high reliability in any environmental conditions.

Composed of standard, easy to check elements, it provides simplification. The device is also easy to set up and check Q.

Claims (3)

Invention Formula I. Device for protection of an electric motor against overload, containing a current transformer, the primary winding of which is included in one of the phases of the power supply network to which the series-connected starter coil, elements are connected five "Start and Stop, power closing contacts of the actuator included in the stator circuit of the electric motor, output relay, the closing contact of which with the first closing contact block of the actuator connected in series, is connected parallel to the Start element, characterized in that, in order to increase reliability, noise immunity, it is additionally equipped with a switching element made on an overcurrent relay, connected by its output to the secondary winding of a current transformer, with a three-phase rectifier whose input is included in the stator circuit of an electric motor, two capacitors, five resistors, and the output relay is double-wound with magnetic memory, with the first winding of the output relay connected to the output of the switching element through a series of disconnecting contact of the Start, the first capacitor parallel to which the first the second resistor, the second resistor, and the second 0 the coil is connected to the output of the three-phase rectifier through the second closing contactors of the actuator, the second capacitor in parallel with which the third resistor, the fourth resistor, in parallel to the sequentially connected disconnecting element of the Start element and the first winding of the output relay the fifth resistor is connected in series. 2. The device according to claim 1, characterized in that the switching element is made on an overcurrent relay, the closing contact of which is included in the circuit of the first winding of the output relay through a zener diode. 3. The device according to claim 1, characterized in that the switching element is made on a rectifier, the input of which is connected to the secondary winding of a current transformer, a smoothing capacitor, a resistor connected in parallel to the output of the specified rectifier and a zener diode connected in series with the second capacitor to the output of the rectifier Met. / fig. 2 / fig. 2