SU1764118A1 - Out-regime protecting device for three-phase induction electric motor - Google Patents

Abstract

Usage: in the relay protection schemes of three-phase electric motors from abnormal conditions. SUMMARY OF THE INVENTION: In a device for protecting a three-phase asynchronous electric motor from abnormal operating conditions, a current sensor is made in the form of a current transformer, the latter is configured to be mounted on the electric motor to provide thermal contact with the electric motor at a temperature control point, while the core of the current transformer is made of ferromagnetic material with a given Curie point, which allows to expand the functionality of the device by providing temperature Protecting electric motor .2 yl.

Description

The invention relates to electrical engineering, in particular, to devices for protecting three-phase electric motors from an abnormal condition, and can be applied where control over the operation of an engine is limited or absent.

A device for protection of a three-phase asynchronous electric motor against abnormal operating modes is known, comprising a current sensor and a start time sensor, the output of which is connected to a control electrode of a thyristor connected in series with the first executive relay, a second executive relay connected in parallel with the inputs of the start time sensor and the current sensor outputs . Limited functionality is a disadvantage of this device.

The closest in technical essence to the invention is a device for protecting a three-phase asynchronous electric motor from abnormal conditions.

The work contains a magnetic starter with power contacts, magnetic starter controls made in the form of Start and Stop buttons, a power source made in the form of rectifiers, capacitors, an executive relay, a diode, resistors, a current sensor and a reacting element. Limited functionality is a disadvantage of this device.

The purpose of the invention is to expand the functionality by providing thermal protection for the motor.

The goal is achieved by the device for protecting a three-phase asynchronous electric motor from abnormal operating conditions, which contains a magnetic starter, the power contacts of which are intended to be connected to the supply lines of the electric motor from the mains, V1 O circuit

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a cathel, a current sensor, made in the form of a current transformer, intended to be connected to the supply line of one of the motor phases, and an actuator with an output contact, the actuator input connected to the current sensor output, and its output contact connected to the magnetic actuator holding circuit, the current transformer is configured to be mounted on an electric motor with ensuring thermal contact with the electric motor at the point of temperature control, while the core of the current transformer is made of ferro of a rotten material with a given Curie point.

FIG. 1 and 2 show various embodiments of the proposed device for protecting a three-phase asynchronous electric motor against abnormal operating conditions.

The device (see Fig. 1) contains a magnetic starter 1, a stabilized power source 2, which includes a limiting capacitor 3, a rectifier 4, the first smoothing capacitor 5, a zener diode b, an unbalanced trigger on transistors 7 and 8, into a low-voltage device. which included the executive relay 9, the closing contacts of which are connected in parallel to the Start button 11 of the magnetic starter 1, and the transistor 12 so that the executive relay 9 and the transistors 8 and 12 form a series circuit, a small transformer current 13, Used as a current sensor, a diode 14 used as a controlled signal rectifier, a second smoothing capacitor 15 to which the input of transistor 12 is connected via the setting mode of the resistor 16 and the trigger input through a chain consisting of resistors 17 and 18 and the third a smoothing capacitor 19, serving to limit and smooth the control signal at the trigger input. The small current transformer 13 is located on the housing or on the windings of the electric motor. The core of the current transformer 13 is made of ferromagnetic material with a Curie point equal to the maximum allowable temperature of the electric motor at the location of the current transformer 13.

The device works as follows.

Start and normal mode.

When the Start button 11 is pressed, the magnetic starter 1 is activated, the electric motor 20 and the power source 2 are connected to the mains. The rectified and smoothed signal of current sensor 13 opens

transistor 12 is not saturated until the triggering, because the smoothing circuit on resistors 17 and 18, and smoothing capacitor 19 does not allow the trigger input signal to exceed its breakdown threshold at the moment of inrush current.

Thus, at the time of launch, the trigger remains in its original state, in which

the transistors 8 and 12, connected in series with the relay 9, are open at the same time, the relay 9 is activated, the contact 10 closes the supply circuit of the magnetic starter 1, leaving the electric motor 20

connected to the network. In normal operation of the electric motor 20, the signal at the trigger input is limited by a divider on resistors 17 and 18 to a value lower than the threshold tilting trigger, which

provides an on state of the electric motor 20.

Overload mode

In the overload mode of the electric motor 20, the current in all phases of its power supply exceeds

the permissible value and the control signal reaches a value sufficient to trip the trigger, the transistor 7 opens and the transistor 8 closes, de-energizing the relay 9, pins 10 of which

open, disconnecting the magnetic starter and with it the electric motor 20 from the network. The device is tuned to a specific value of the permissible current at which it should operate, is carried out or

changing the flip-flop threshold using a resistor 21 or changing the value of the control signal at its input using a divider on resistors 17 and 18. Mode with phase breaks,

The interruption of one of the phases in which the current transformer 13 is not connected, anywhere, starting from the electric motor 20 and to its power source, significantly increases the current through the transformer and the control signal, which becomes sufficient to trip the trigger. In this case, the transistor 8 is closed, the relay 9 is de-energized, in., As a result, the magnetic starter 1 and the electric motor L will be disconnected from the network. Breakage

the phase in which the current transformer 13 is connected, in any place leads to the disappearance of the current in the transformer 13 and, accordingly, the control signal, the transistor 12 is closed, the relay 9 is de-energized, ensuring that the magnetic starter 1 and the electric motor 20 are disconnected from the network. Breaking more than one phase in any combination leads to the disappearance of the current through the transformer 13 and the control signal, locking the transistor 12, providing the relay 9, disconnecting the magnetic starter 1 and the electric motor 20 from the mains.

Short circuit mode.

Any combination of short circuits, starting with the electric motor and prior to its power source, leads to the disappearance or unacceptable increase in the current in the transformer 13 and the control signal, which will lead to the closing of the transistor 12 or 8, respectively, and eventually to the magnetic motor 1 and the motor 20 off the net.

Temperature protection mode of the motor.

When the maximum permissible temperature is reached by the electric motor 20, the core of the transformer 13 loses magnetic properties (this happens when the core reaches the Curie point), which causes the control signal to disappear, transistor 12 closes, de-energizes relay 9 by disconnecting the magnetic starter 1 and the electric motor 20 from the network.

The device shown in FIG. 2, contains current sensor 1, rectifying diode 2, first executive relay 3, variable resistor 4, capacitor 5, second executive relay 6, thyristor 7, Zener diode 8, starting block 9, contact 10 of the executive relay 3, contacts 11 of the executive relay 6 , start button 12 of starting unit 9. A second executive relay 6, a start time sensor input and a circuit consisting of a series of first executive relay 3 and a thyristor 7 are connected in parallel to the output of current sensor 1. The control electrode of the thyristor 7 is connected to the output of sensor and the start time. The current sensor consists of a current transformer 1 and a rectifying diode 2 and serves to ensure the operation of the device with an unacceptable overload of the electric motor and the loss of one of the phases, as well as providing power to the device circuit.

The primary winding of the current transformer 1 is connected in series to any of the phases of the supply network and may have taps that are used in protecting electric motors of various capacities.

The secondary winding of the current transformer 1, serially connected to the rectifying diode 2, is the output of the current sensor.

A start time sensor is an integrating circuit consisting of a variable resistor 4 and a capacitor 5, the output of which includes a Zener diode 8. Normally open contacts 11 of the executive relay 6 are connected in parallel

button 12, the start-up of the starting block 9, and are designed to turn off the electric motor when the phase in which the current transformer 1 is connected is turned on.

5Normally closed contacts of the executive relay 3 are included in the power supply circuit of the starting block 9 and are designed to turn off the electric motor in case of unacceptable overloads and running phases.

These are not included in the current transformer 1. The current transformer 1 is located on the motor case or on its windings, while the current transformer core 1 is made of a ferromagnetic material with a Curie point equal to the maximum allowable temperature of the motor in the location of the current transformer.

The device works as follows.

The initial state - the load is disconnected, there are no currents in the linear wires A, B, C, there is no voltage at the current sensor output, no current passes through the coil of the starting unit 9.

Start - when you press the Start button 12, the starting block 9 is triggered, the starting current of which passes through the linear wires A, B, C. always larger than nominal. A voltage appears at the output of the current sensor, the relay 6 is activated and the contacts 11 bypasses the Start button 12, the starting block remains in the on state. To protect the relay 3 from being triggered5, at the moment of inrush current, a start time sensor is provided with a corresponding setting of the time constant value by changing the resistance of the resistor 4.

0 Stationary mode. The load current is nominal, the voltage at the output of the sensor ensures reliable activation of relay b, but below the threshold of the Zener diode 8 of the start-up time sensor circuit. Thyristor 7

5 is closed. Relay 3 is de-energized. Contacts 10 are closed.

Emergency break of a linear wire. The process is the same for wires A and B - in

In this and other cases, through the current transformer 1 increases, the voltage at the output of the current sensor and the output of the start time sensor increases, exceeding the threshold of the Zener diode 8, the thyristor 7 opens, the relay 3 is activated, the contacts 10 open and break the power supply circuit of the starting unit 9 The motor is disconnected from the network. When a linear wire C is broken, relay 6 de-energizes, contacts 11 are open. breaking the power supply circuit of the starting unit 9, the motor is disconnected from the network.

Mode unacceptable motor overload. In this case, the current increases significantly in all phases of the network, the voltage at the output of the current sensor increases, and the process of switching off the electric motor in this mode is similar to the case of broken line wire A or B, and the acceptable overload of the electric motor is determined by the threshold of the Zener diode 8 the start time sensor, and the allowable overload time is determined by the constant integration time of said sensor.

Temperature protection mode of the motor. When the maximum allowed motor temperature reaches the current transformer core 1 loses magnetic properties (this happens when the core temperature reaches the Curie point), which de-energizes the relay b relay, contacts 11 of which open, breaking the power supply circuit of the starting unit 9. Shut-off motor - is from the network.

The use of the proposed technical solution allows to extend the functionality of the device for

by providing thermal protection for the motor.

Claims (1)

The device for protection of a three-phase asynchronous electric motor against abnormal operating modes, contains a magnetic starter, the power contacts of which are intended to be connected to the supply line of the electric motor phases from the supply network, the magnetic starter on and hold circuit, a current sensor made in the form of a current transformer designed for the inclusion in the supply line of one phase of an electric motor, and an actuator with an output contact, with the actuator input connected to the output A current sensor and its output contact are included in the holding circuit of the magnetic starter, characterized in that, in order to expand the functionality by providing thermal protection of the electric motor, the current transformer is adapted to be mounted on the electric motor to provide thermal contact with the electric motor at the temperature control point, with This current transformer core is made of ferromagnetic material with a given Curie point. A sun 1 FIG. 2