SU1408493A2 - Abnormal duty protection device for induction motor - Google Patents

Abstract

The invention relates to a relay protection technique and is intended to protect induction motors from overloads, operating on two phases, as well as from unacceptable heating of the windings. The purpose of the invention is to expand the scope. The goal is achieved by the fact that instead of the start-up winding of the reed switch, an electromagnetic relay is introduced with a break contact in the coil circuit of the protected motor and a short-circuiting contact that provides for self-blocking of the relay after tripping. Restarting is possible only after unlocking the relay by briefly pressing a button. The introduction of self-blocking eliminates the possibility of the so-called bell ring effect. The presence of the opening contact in the contactor circuit of the protected motor allows the device to be used for any control circuit, regardless of the type of current and voltage in the control circuit. 1 il. i (L

Description

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The invention relates to the protection of electric motors against overload and short phase, in particular for electric motors with control from an automatic controller or from any other starting device, and is an improvement of the device according to author. No. 1330694.

I The purpose of the invention is to expand the scope of use by providing a self-blocking device after an e-operation during abnormal modes, i. the possibility of using electric motors of different power for sending, regardless of the type of current, voltage value and control circuit.

The drawing shows the safety scheme of an asynchronous motor protection device.

The device contains a control unit 1 (the circuit, the type of current and the voltage value of the unit can be any), energizes the coil 2 of the starting contact, the main contacts 3 of which are included in phases A and B of the motor power supply A &B; The winding of the sensor 5 fok, the secondary winding of which is connected to the rectifier 6 and through it feeds the electronic key 7, which controls the reed switch 8 with the clamping contacts 1: which is connected in series with the coil 9 of the executive electromagnetic relay 10, which has a short circuit 1 and breaker 12 contacts.

Coil 9 of the relay is connected to the zero EJOMy wire and through the disconnecting idoHTaKT reed switch 8 to phase C after the contacts of the contactor 3 and simultaneously through the closing contact I1 and the unlocking button 13 to the phase C to the contacts 3 of the contactor. The closing contact 12 of relay 10 is connected to the supply circuit of coil 2 of the contactor.

The electronic switch 7 contains a key transistor 14, in the collector circuit of which the winding 15 of the reed switch 8 is connected, which through a resistor 16 is connected to the rectifier 6, the base of the key transistor 14 through posistors 17 located in the front of the winding of the electric motor 4 (6a the circuit for simplification shows only one posistor) and through a resistor 18 is connected to the collector 19 of the control transistor 20 The collector 19 of the transistor 20 through the resistor

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2 is connected to the rectifier 6, and resistors 22 and 23 and a capacitor 24 are connected to the base of the transistor.

The device works as follows.

When applying voltage from the control unit I to the coil 2 of the contactor, the contacts 3 of the contactor close and connect the windings of the electric motor 4 to the mains. After the contacts 3 are closed along the circuit: neutral wire, coil 9 of relay 10, closing contact of reed switch 8, phase C, a closed circuit is formed, through which current will flow under the action of phase voltage (phase C and zero wire). However, the relay 10 does not work, because after closing the contacts 3 under the action of the starting current of the electric motor in the secondary winding of the current sensor 5, the voltage under which the current flows will go through the winding 15 of the reed switch 8 and its contact will open before the relay can operate 10, since the response time of the reed switch is more than an order of magnitude shorter than the response time of the electromagnetic relay. Therefore, after starting the motor, contact 11 remains open and contact 12 is closed,

In normal operation, the motor. 4 due to the current flowing in phase C at the output of the sensor 5 through the Vits voltage, which, after rectification, is applied to the winding 15 of the reed switch along the circuit: plus rectifier 6, resistor 16, winding 15 of the reed switch, key, transistor 14, minus top mitel. The parameters of the electronic key 7 are selected in such a way that in normal operation of the electric motor 4 due to the voltage applied to the electronic key 7, the key transistor 14 is opened and the minimum current flows through the control transistor 20.

When the motor 4 is overloaded, the current in phases A, B, C increases, the voltage at the output of current sensor 5 increases. An increased voltage applied to the electronic key 7 causes an increase in the voltage drop across the resistor 16. The voltage from the resistor 16 through the resistor 22 is applied to the capacitor 24 and the base of the control transistor 20. The base current of the control

the transistor 20 increases the voltage drop across the resistor 21 and the key transistor 14 closes. The current of the key transistor 1D is terminated through the control winding 15 of the reed switch 8, the contact of which returns to the initial state, i.e. closes The coil 9 of the executive relay 10 receives power, which, having triggered, will switch its contacts: by opening the contact 12, the circuit of the coil 2 of the contactor is broken, which opens the contacts 3 and disconnects the electric motor from the network; the closure of the contact 11 on the coil 9 of the relay 10 will be powered from phase C through the unlock button 13. Relay 10 is activated and turned on when turned on, i.e. it is self-locking.

Engine 4 cannot be restarted because contact 12 of relay 10 is open. In order to prepare for restarting the engine 4, it is necessary to unlock turnips 10 by pressing button 13. After a short break in the power supply circuit of coil 9 of relay 10, it returns to its original state, i.e. contact 11 is open, and contact 12 is closed. Since the contacts 3 of the contactor are open, and the contacts of the reed switch 8 are closed, the circuit is ready for re-injection.

When an A or B phase is broken, the current in phase C increases, and the device operates by disconnecting the motor 4 from the power source,

When phase C is lost, the supply voltage of the device from the current sensor 5 disappears and the contact of the reed switch 8 returns to the initial state, i.e. closes, which causes the actuation of the actuating relay 10 and the switching off of the electric motor 4. The capacitor 24 provides the time delay and the operation when the electric motor starts, i.e. detuning from start-up currents. The magnitude of the device operation current setting is set by resistor 22.

When the temperature of the motor windings increases to the maximum allowable, the posistor 17 heats up, the resistance of which increases sharply in this case, the base current of the key transistor 14 decreases, it closes c. The current through the winding 15 of the wind chamber 8 stops, the contact of which is closed.

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which causes the activation of the ns supplementary relay 10 and the switching off of the electric motor 4,

Thus, the introduction of an electromagnetic relay 10 into the circuit eliminates the ring effect and creates a new positive feature: the protection now has a self-blocking, i.e. in case of protection device operation in case of overcurrent or winding temperature, it is impossible for the operator to re-turn on the electric motor until the relay is unlocked, i.e.

5 BEFORE pressing button 13. This button is located along with the starting equipment in the switchboard and is serviced by an electrician, who is required to pre-locate and eliminate the equipment.

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If there is a button 13 that is included in the circuit of the coil 2 of the contactor of the protected motor, the device maintains the self-monitoring property. If the device is found defective, t, e, when the engine is started, the contact will not open. the reed switch, the electromagnetic relay 10 will operate and its contact 12 will open the power supply circuit of the coil 2 of the contactor.

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Claims (1)

Invention Formula Device for protection of asynchronous electric motor from abnormal mode in accordance with the author, no. 1330694, characterized in that, in order to expand the scope of application, it is additionally introduced an executive electromagnetic relay, the coil of which is connected at one end to a terminal for connecting to the neutral wire mains, the other end through the disconnecting contact of the reed switch - with the terminal for connecting to the phase conductor of the mains supply, the disconnecting contact of the relay is connected to the circuit of the contactor coil, and the closing contact is connected to ochke compound interrupter reed contact and actuator coil of the electromagnetic relay and the other end is connected through a release button - to the terminal for connection to a power line phase conductor to the power contacts of the contactor. And in CO 999 Editor S.Patrusheva Compiled by K. Shilai Tehred A. Kravchuk Proofreader E. Lonchakova Order 3358/55 Circulation 650 VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Subscription