SU71956A1 - Device for automatic control of synchronized asynchronous motor - Google Patents

Description

The most effective way to increase the power factor of asynchronous motors and electrical systems in which induction motors operate is to synchronize these motors.

The introduction of an asynchronous motor in synchronism is achieved by supplying the rotor windings with a constant current of the appropriate size.

The main reasons that delayed the development of synchronization of asynchronous motors are: a) electrical parameters of the excitation current (high ampere of low voltage), since until recently there was no corresponding current source for this purpose; b) the possibility of engine damage that has fallen out of synchronicity during an overload or a decrease in the mains voltage.

The present invention eliminates both causes inhibiting the spread of synchronous asynchronous motors.

The proposed synchronization scheme (referred to by the authors as the “DAG scheme”) uses as the source of direct current an excitation: these are solid (mainly selenium) rectifiers. It is precisely the low voltage and high current that are the most advantageous parameters for the selenium valves, connected according to certain schemes and in a proper design.

The scheme for automating the synchronization process, applied in the proposed device and constituting the essence of the proposed invention, excludes the operation of the engine under unspecified modes, and thus the possibility of its damage. This scheme provides for the use of a relay system automatically advancing the rectifier to the mains supply at low values of the motor slip.

The essence of the invention is that the relay system contains two AC relays, one of which is connected to the stator circuit of the engine and serves to turn on the rectifier to the network at low engine loads, and the other to the rotor circuit mitel and for short No. 71956

whom closes the rotor circuit in case of engine failure out of synchronicity during overload.

FIG. Figure 1 shows the selenium rectifier unit used in the proposed device; in fig. 2 is an electrical circuit of the latter, made in accordance with the invention.

The synchronization unit (Fig. 1) consists of: a selenium rectifying part / and a transformer 5, arranged in one casing 3.

The selenium rectifier is mounted from the estimated number of aluminum plates on which the selenium washers are attached.

The synchronization transformer, with a capacity of up to 20 kVA, has a high-voltage side of 380/220 V, from which several additional spurs are made, which allow to obtain a voltage on the low-voltage side from 6 to 12 b.

The synchronization unit provides for the possibility of switching selenium elements, constructively carried out by reconnecting them inside the casing. Due to this, a three-phase half-wave rectification or a phase-flashing can be achieved by connecting the rectifier according to the three-phase Larionov scheme.

To obtain the current curve with a small ripple, the use of the Larionov scheme makes it possible to obtain additional values of the rectified voltage up to 20 V. This may be necessary when synchronizing high-voltage motors that have relatively high resistance windings on the rotor.

In the diagram in FIG. 2 is designated: M - controlled asynchronous motor; CB — Selenium synchronization unit feeding the engine excitation circuit; YAR - vice rheostat; 7Gs - current transformer R of the stator motor circuit; ТТ „- current transformer in the rotor circuit; NM - magnetic starter: PS - block-contact synchronous pezhim; SL - signal lamp; KSh - shunt contactor; PC is an engine injection relay; PB is a synchro relay; OC - relay intermediate.

The circuit (Fig. 2) automatically performs the following operations: a) after a normal asynchronous start-up, the introduction of the motor M into the synchronous mode of operation; b) the introduction of the motor M in asynchronous mode with overloads or voltage drops in the mains supply, more than the permissible norms; c) introducing the motor M in synchronism when the load drops to nominal and below or establishing a normal voltage in the network supplying the synchronized motor.

The scheme works as follows.

The asynchronous motor is started up in the usual way. At the moment of switching on the STARTING apparatus, a voltage is applied to the coil of the shunt contactor KSh and the contactor closes the open phase of the rotor. ; .-. .

With the introduction of the last section of the Yar rheostat, they gamble - at a short time the rotor winding. The next movement of the rheostat hand closes the BS contact (instead of the contact, an ordinary start button can be installed on the rheostat), so that the voltage on the coil of the NM magnetic starter will be applied through the normally closed contacts of the OV relay. The magnetic NM actuator will turn on the synchronization selenium aggregate CB and at the same time, with some advance at the expense of the contactor's response time, break the KS contactor circuit, as a result of which direct current flows into the rotor and the motor is synchronized.

When overloading, more than the permissible limit, or when the voltage drops in the network above the established norms, the engine falls out of sync. Due to the slip in the rotor winding, an emulator is excited, creating an alternating current in the rotor circuit.

This alternating current, the winding around the transformer winding TTR, actuates the relay RV and the last closes the circuit of the RP relay coil. When the RP relay operates, its normally closed contacts break and the coil circuit of the magnetic actuator of the actuator is de-energized. The magnetic starter is turned off and turns off the synchronization selenium unit. At the same time, when PM is disconnected, its block contacts close the coil circuit of K.Sh., the latter turns on and closes the open rotor phase, closes all three phases of the rotor winding, and the motor starts to work in normal asynchronous mode.

Loss of synchronism due to overload or voltage drop in the 1st mains supply is accompanied by an increase in the current in the stator circuit. As a result, the PC current relay operates and supplies voltage to the self-locking block contact of the OL relay; therefore, the OL relay will be held until the current in the stator circuit is reduced to nominal.

When the load decreases, the current in the stator circuit of the motor decreases, the PC relay contacts open and switch off the RP intermediate relay. Normally closed contacts of the relay RP closed circuit magnetic starter PM, which will include synchronization selenium unit. The block contacts of the magnetic actuator PM are open the circuit of the coil of contactor K, W, which opens the shunt circuit of the rectifier contact, i.e., the synchronous circuit is restored.

One of the advantages of the DAG scheme is the ability to automatically pick up the most favorable moment of switching the current into the rotor circuit, namely, at the moment of passing the current in the phase to which the double excitation current passes through zero. The presence of a current transformer in the rotor circuit allows the use of a current relay (within b) as a relay Pb.

Subject invention

A device for automatic control of a synchronized asynchronous motor having a phase rotor powered by direct current from a solid (mainly selenium) rectifier, in order to increase the power factor of the installation, using a relay system that automatically switches the rectifier to the supply network at small slip values motor, characterized in that said relay system contains two alternating current relays, the first of which is connected to the stator circuit of the motor and serves to carry out VC Switching the rectifier to the mains at nominal and lower engine loads, and the second to the rotor circuit, serves to automatically switch off the rectifier and short-circuit the rotor circuit in the event of an engine falling out of sync with overload.

 - 3 -jYo 71956

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