RU137694U1 - DEVICE FOR BRANDLESS OPENING OF CONTACTS OF STATOR WINDING CONTACTORS OF ASYNCHRONOUS MOTOR - Google Patents

Abstract

The utility model relates to electrical engineering and can be used in AC electric drives based on an asynchronous electric motor, both with a squirrel-cage and with a phase rotor when powered, both from an industrial network and from a power source such as a diesel generator.

The technical task is to eliminate overvoltages arising from the opening of the contacts of the stator circuit contactors when disconnecting or reversing asynchronous electric motors, which are dangerous for autonomous energy sources of limited power such as diesel generators, as well as causing sparking of the contacts, premature wear, cost of spare parts and repair downtime.

This problem is solved by the fact that the star of the stator winding of the electric motor is open, and the disconnected ends of the stator phase windings are connected to the thyristors connected in a triangle, the control electrodes of which are connected to the outputs of the logic controller unit, the contactors coils are also connected to the corresponding outputs. When the motor is reversed, first thyristors are closed, opening the star of the stator circuit, interrupting the flow of current in the stator circuit, after a time delay the contactor of the previous direction of rotation is turned off, then the contactor of the opposite direction of rotation is turned on, and then the thyristors are turned on, closing the ends of the stator windings to the star, the motor is accelerated into the opposite side. When the motor is turned off without reverse, everything happens as with reverse only without turning on the contactor of the opposite direction of rotation.

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Description

The utility model relates to electrical engineering and can be used in AC electric drives both non-reversible and reversible based on an asynchronous electric motor, both with a short-circuited and with a phase rotor when powering the electric motor, either from an industrial network or from an autonomous power source such as a diesel generator of limited power, comparable with the power of electric motors supplied from it, installed on a moving object, for example, a crane on a motor vehicle or caterpillar.

Known control devices for asynchronous electric motors (Yaure A.G., Pevzner E.M. Crane electric drive. Handbook. - M .; Energoatomizdat, 1988. - 344 pp. Il. On page 316). In these devices, in addition to contactors, thyristors are installed in the stator circuit, which are used to control the motor speed and provide non-current switching of the stator circuit contactors. Speed regulation is ensured by the thyristor changing the voltage on the motor stator, which varies from the nominal value and below. As the voltage across the motor stator decreases, its torque decreases in a quadratic manner. To maintain a given speed, it is required to install an engine speed sensor (tachogenerator) and make a closed regulation system. When controlling the speed, cosφ decreases, higher harmonic components appear in the voltage at the motor stator. Therefore, such schemes, despite their simplicity, are not widely used. To use it only for currentless switching of contacts of contactors is irrational due to the large number of required thyristors. Of course, if the presented circuit is oriented only at the currentless switching of contactors, then the number of required thyristors can be reduced to four.

The closest to the presented utility model, the prototype is a device for controlling a reversible electric motor (RF Patent No. 20111285 IPC 7 H02P 1/40, publ. 04/15/1994). The device contains delay relays, thyristor switches with make contacts, delay relays in thyristor control circuits, Forward and Back contactors with two make and break contacts each, two Start Forward and Start Back buttons, made in the form of interlocked make and make contacts each.

The disadvantage of this device is the complexity of the thyristor switches and the presence of delay relay contacts in the control circuit of the thyristor thyristor switches.

The claimed solution is based on the technical task of simplifying the circuit of thyristor switches and eliminating contacts in the thyristor control circuits.

The specified technical problem is solved by the fact that the star of the stator winding of the electric motor is opened, and the disconnected ends of the windings of each phase of the stator are connected to the thyristors connected into a triangle. When voltage is applied to the control electrodes of all thyristors, the thyristors are turned on, the ends of the phases of the stator windings with the connected thyristors are connected to a star, and the motor is operating normally. When voltage is removed from the control electrodes of all thyristors, they are locked, and the ends of the phases of the stator windings with the closed thyristors open, preventing current from flowing through the phases of the stator and the contacts of the contactors. In this current-free state, the contactors can be turned on, off and switched, which ensures a current-free contact closure / opening of the contactors.

The essence of the utility model for the reversible motor control option is illustrated in the drawing, which shows a functional diagram of the device.

The asynchronous electric motor is powered from the energy source 1. Contactors 2 and 3 provide the connection of the electric motor, respectively, for forward and reverse rotation. Switching the contactors provides a change in the phase rotation of the stator windings A-X, B-Y, C-Z of the electric motor 4 and. as a result, a change in the direction of rotation (reverse) of the electric motor. The ends X, Y and Z of the stator windings are connected to the thyristor block 5. The thyristors 6, 7 and 8 of the thyristor block are connected in series with each other in a closed triangle. The logic controller unit 10 controls the thyristors 6, 7 and 8 of the thyristor unit 5. The coils 11 and 12 of the contactors 2 and 3, respectively, are also controlled by the logic controller unit 10. The signals “Forward” or “Back” from the control unit of the electric motor 9 (command device) are sent to block 10 or facility management automation system). In the initial state, in the absence of the “Forward” and “Backward” commands, the contactors 2 and 3 are disconnected, the thyristors 6, 7 and 8 are locked, the stator windings of the motor 4 are not flowed around by the current, the motor is stationary. When a command, for example, “Forward,” is sent to the logic controller unit 10, voltage is immediately applied to the coil 11 of contactor 2. Contactor 2 closes its contacts by supplying voltage to the stator of the electric motor, but the motor does not turn on, since the thyristors of block 5 are locked. After a time delay exceeding the turn-on time of the contactor, the logic controller unit 10 supplies voltage to the control electrodes of the thyristors 6, 7 and 8. The thyristors open by connecting the ends X, Y and Z of the phases of the stator windings to the star, the electric motor turns on and operates in normal mode. When the “Forward” command is removed, the logic controller unit 10 removes voltage from the control electrodes of the thyristors, the thyristors are locked, the current flows through the stator winding of the electric motor, and only then, after a time delay, the voltage is removed from the contactor coil and the contactor is disconnected if there is no current flow through its contacts (non-current shutdown). The device works similarly when submitting and removing the "Back" command. If the electric motor rotated by the “Forward” command, but the “Forward” command was removed and the “Back” command was issued, the device operates as follows. The voltage is removed from the control electrodes of the thyristors, the thyristors are locked and after a time delay the contactor is turned off for forward rotation, then the contactor is turned on for reverse rotation and only then is the voltage applied to the thyristor control electrodes. Thus, when switching contactors, the delay time for turning on the thyristors must be greater than the total time for switching off and on the contactors.

A variant with a non-reversible electric motor differs from the presented version with a reversible electric drive only in that there is no one of the contactors with its coil and there is no connection at the input of the logic controller unit for the opposite direction of rotation of the electric motor.

A currentless disconnection of the contacts eliminates the occurrence of overvoltages when the active-inductive load is disconnected, which is the stator circuit of an asynchronous electric motor, since the thyristors are locked when the thyristor current is gradually reduced to zero. These overvoltages are especially dangerous for autonomous power supplies with voltage and frequency regulators with a power comparable to the power of the motors fed from it. In addition, since currentless disconnection eliminates the sparking of contacts when they are disconnected, premature contact wear, spare parts costs and repair downtime are eliminated.

A useful model solves the following tasks:

- minimization of the number of thyristors for currentless switching and switching contactors;

- elimination of overvoltage when disconnecting an active-inductive load, which is the stator circuit of an induction motor, which is dangerous for operating equipment, in particular, autonomous energy sources of limited power such as diesel generators with voltage and frequency regulators supplying asynchronous motors;

- the elimination of sparking of contacts when they open, causing premature wear of the contacts, the cost of spare parts and repair downtime.

The utility model is used to control asynchronous electric motors, both with a squirrel-cage and with a phase rotor, at which the beginnings and ends of the stator windings are derived, when powered from an industrial network or from an autonomous power source such as a diesel generator.

Claims (1)

A device for currentless opening of the contacts of the stator winding contactors of an asynchronous electric motor, including a contactor for a non-reversible motor or two contactors for a reversible electric motor, connected to an energy source, characterized in that the star of the stator winding of the electric motor is open, and the disconnected ends of the windings of each stator phase are connected to the thyristor unit, thyristors connected in a triangle, the control electrodes of which are connected to the outputs of the logic controller unit, to correspond conductive outputs of which are connected also the coil of the contactor or contactor coil, and the input logic controller unit circuit connected to the output of the motor control unit.

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