CS240252B1 - Connection of electronic circuit for asynchronous motor - Google Patents

Abstract

Connection of an electronic circuit for an asynchronous motor, the purpose of which is to enable operation of the asynchronous motor at reduced speeds at reduced costs while ensuring good stability of the reduced speeds. The above is achieved by the first power terminal (u) of the asynchronous motor (1) being connected via the first contactor (4) through a series combination of a switch (5), a member (6) with adjustable impedance and a second contactor (7) to the first power phase (U), and via the third contactor (8) to the first power phase (U), the second power terminal (v) of the asynchronous motor (1) being connected via the first contactor (4) through a series combination of a switch (5) and a second contactor (7) to the second phase (V), and via the third contactor (8) to the second power phase (V), and the third power terminal (w) of the asynchronous motor (1) being connected via the first contactor (4) through a series combination of a second contactor (7) to the neutral power conductor (N), and via the third contactor (8) to the third power phase (W), with the output of the speed relay (3) being connected to the input of the switch (5).

Description

The present invention relates to an electronic circuit for an asynchronous motor enabling operation of said motor at a lower speed.

Working machines powered by a three-phase asynchronous motor require, in some cases, their operation to be at a lower speed than said number of poles of said driving motor.

This requirement is currently addressed, for example, by means of reduction gears of various designs between the driving motor and the working machine, which are generally controlled by an electromechanical switching device. Another solution is to use a special asynchronous motor, in which the number of poles and thus its speed is selected by the switch. More recently, non-contact power frequency converters have been used to control the speed of asynchronous motors in some applications. The common disadvantage of these solutions is their relatively high complexity and laboriousness and the demand for building space and price.

These drawbacks are largely eliminated by the wiring of the electronic circuit for an asynchronous motor according to the invention, the principle being that the first power terminal of the asynchronous motor is connected through a first contactor, through a series combination of switch, impedance adjustable element and second contactor with first powered phase. through the third contactor with the first supply phase, the second supply terminal of the asynchronous motor is connected through the first contactor, both through a series combination of switch and second contactor to the second supply phase, both through the third contactor to the second supply phase and third supply terminal of the asynchronous motor a contactor, on the one hand through the other, a contactor to the neutral supply conductor, on the other hand, via the third contactor to the third power supply phase, the output of the rotary relay being connected to the switch input.

An advantage of connecting the electronic circuit for an asynchronous motor according to the invention is that it enables the asynchronous motor to be operated at a reduced speed at a relatively low cost, said reduced speed having a relatively good stability.

The wiring of the asynchronous motor electronic circuit is shown in the drawing.

The connection comprises a three-phase asynchronous motor 1 connected or at least star-connected, to whose shaft a rotary relay 3 is connected by a flexible coupling 2. The first power terminal of the asynchronous motor 1 is connected via a first contactor 4 and the second contactor 7 to the first power supply phase U, on the one hand through the third contactor 8 to the first power supply base U. The switch 5 is preferably a two-phase contactless switch and an adjustable impedance member 6, for example a resistor or adjustable air gap choke; preferably a single-phase tapped autotransformer.

The second power terminal in the motor 1 is connected via the first contactor 4 both through a series combination of switch 5 and the second contactor 7 to the second power supply phase V and through the third contactor 8 to the second power supply phase V. The third power terminal w of motor 1 is connected through the first contactor. 4, through the second contactor 7 to the neutral supply conductor N, and through the third contactor 8 to the third supply phase W. The output of the rotary relay 3 is connected to the input of the switch 5.

During normal operation of the motor 1, i.e. at its rated speed, the first and third contactors 4, 8 are closed, so that the motor 1 is supplied in a known manner with a full three-phase voltage. In the case of low speed, the third contactor 8 opens and the second contactor 7 closes. In this case, the motor 1 is supplied only by the phase voltage, i.e. the voltage between the neutral conductor N, for example one of the third phase W. To generate a torque field and sufficient starting torque At the same time, a second auxiliary phase, selected according to the speed, is connected by the second contactor 7, but the current is reduced by the adjustable impedance member 6.

When the set slow speed is reached, the speed relay 3 switches off the power supply to the motor 1 via switch 5, the speed starts to decrease until the speed relay 3 switches on again at the set delay time of the speed relay 3. The inertia moment of the whole system, comprising the motor 1 and the working machine (not shown), maintains a speed with negligible variations around the set mean value.

The first switch 4 has only a protective function in the circuit. It can be realized either by a three-phase circuit breaker or it can be replaced by three fuses.

Claims (1)

Ρ Ř Ε D Μ É Τ Connection of an electronic circuit for an asynchronous star-connected motor to whose shaft a rotary relay is connected by a flexible coupling, characterized in that the first power terminal (s) of the asynchronous motor (1) is connected via the first contactor (4J) through serial switch combination (5) , an adjustable impedance element (6) and a second contactor (7) to the first power supply stage (U), both via a third contactor (8 j to the first power supply stage (U), and a second power terminal (v) of the asynchronous motor (1) over SUMMARY OF THE INVENTION The first contactor (4) both through a series combination of a switch (5) and a second contactor (7) to a second supply phase (V) and a third contactor (8j to a second supply phase (VJ and a third power terminal) ) is connected via the first contactor (4), secondly via the second contactor (7) to the neutral supply conductor (N), and secondly through the third contactor (8) to the third power supply phase (WJ), relay (3J.