RU6289U1 - THREE-PHASE ASYNCHRONOUS MOTOR PROTECTION DEVICE - Google Patents

Abstract

A device for protecting a three-phase asynchronous motor, in particular, mainly during a phase failure, containing a magnetic starter, Start and Stop control buttons, a rectifier, a relay connected through the rectifier to the circuit between the source and motor zero points, while the contact is open the relay is connected in series with the closing contact of the magnetic starter, characterized in that the inductance is connected in series with the rectifier in the circuit between the zero points of the source and the motor.

Description

The utility model relates to electrical engineering and may find application

protection schemes of three-phase asynchronous motors with phase failure.

Known devices for protecting three-phase asynchronous motors,

containing a matte starter, a control button, a relay whose winding is connected between the source zero points, and a contact in the control circuit, while a capacitor and a primary winding of a transformer with equal reactance are connected in series to a secondary circuit of a transformer, and the transformer secondary winding is connected in parallel two

dinistor L. 1.

It is also known a device for protecting a three-phase asynchronous motor during phase failure, containing a magnetic starter, start and stop control buttons, a rectifier, a relay connected between the zero through the rectifier

points of the source and motor, while the opening contact of the relay is connected in series with the winding of the magnetic starter L. 2.

However, the above devices do not provide reliable starting of the engine, in particular, the device according to L.2 does not exclude the relay being triggered when the engine is started, and to prevent it, it is recommended that the start button be held pressed for a while, which, in turn.

complicates engine starting and, therefore, reduces the reliability of the protection device.

Improving the reliability of the three-phase induction motor protection device can be achieved by various means. These include, for example, the introduction of a time relay with a time delay equal to the start time in fig. 196 L. 2.

A useful model solves the problem of increasing the reliability of a three-phase asynchronous motor protection device in start-ups and operating modes.

To solve this problem, in a device for protecting a three-phase asynchronous motor, in particular, when a phase failure containing a magnetic starter, nyci control buttons and stop, rectifier, relay, incl.

through the rectifier, into the circuit between the source and motor zero points, with a closed contact, the relay contact is connected in series with the closing contact of the magnetic starter, according to the present model, it is possible to include inductance in series between the source and motor zero points in series with the rectifier.

The utility model is illustrated by the example of the drawings, which are respectively: FIG. 1 is a schematic proliferation of the claimed device; FIG. 2 - graphical dependence of changes in voltage; heel and current versus time at the time of engine start; fig.Z is a graphical dependence of the change in voltage and current on time with the disappearance (break) of the phase.

The device for protection of a three-phase asynchronous motor comprises a coil of a magnetic starter 1, its three main contacts 2 and one auxiliary contact 3, control buttons; nyctf button 4 and 5 stop button, rectifier 6, phase-loss relay 7, opening contact 8 of which is connected in series with

by the closing contact of the magnetic starter 1. The inductance 9 is connected in series with the zero points of the source and motor in series with the rectifier 6.

The device operates as follows.

Turning the engine on or off is done by pressing the 4 start buttons or the 5 stop buttons, respectively. During start-up, in addition to the natural asymmetry of phase voltages and currents, asymmetry may also occur due to not strictly simultaneously closing the contacts 2 of the magnetic starter 1 in phases at the moment of switching on. This leads to a sharp appearance of the rectified voltage mhs () of the rectifier 6 and the current in the circuit of the relay 7, which, if there is any

inductance 9 will increase exponentially; where max is the maximum current value;

t L / r is the time constant of the circuit;

L, g are the total inductance and resistance of the circuit, respectively, and will reach the tripping current i p relay 7 for a delay time t greater than or equal to the start time of the motor. When the motor is operating, a current i flows in the relay circuit 7 (Fig. 3), caused by the voltage U at the output of the rectifier 6 with a natural asymmetry of phase voltages. Current i is less than trip current „, relay 7. With

the disappearance (interruption) of the phase at the output of the rectifier 6, the voltage increases sharply from U to U ,,, and the current C increases to 1, also

exponential law for time t «t, cd. When relay 7 is activated

its contact 8 opens in the power supply circuit of the magnetic accelerator 1, which leads to the disconnection of the magnetic starter 1, preventing the engine from turning on.

The inventive device can find application in various types of asynchronous drives.

i S Ia-t / t

  max ®

Literature:

1.Aut. testimonial. No. 418932, MKIN02N 7/08, 1974

2.E.N. Zimin Protection of induction motors up to 500 V, Energy, M.-L., 1967, p. 74-76.

Claims (1)

A device for protecting a three-phase asynchronous motor, in particular, mainly during phase failure, containing a magnetic starter, Start and Stop control buttons, a rectifier, a relay connected through the rectifier to the circuit between the source and motor zero points, while the contact is open the relay is connected in series with the closing contact of the magnetic starter, characterized in that the inductance is connected in series with the rectifier in the circuit between the zero points of the source and the motor.