SU63880A1 - Device for remote switching of three-phase asynchronous motors - Google Patents

Description

As is known, numerous accidents of hand-held electric tools occur due to the unsatisfactory operation of the switch.

So far, it has not been possible to design a satisfactorily operating three-phase circuit breaker for tools such as hand drills and core drills and electric chisels. Western European countries have adopted the use of expensive remote control of such a tool. The present invention pursues the goal of creating a reliable switch that does not require a flexible circuit and is costly and which can be installed in currently operating mechanisms.

In the proposed device, the remote activation of a three-phase asynchronous tool motor is carried out by means of an electromagnetic contactor,

switched on by sequential switching on of the motor winding by the control switch.

It is known that the transient short-circuit current for a two-phase short circuit for an induction motor is (0.85 - 1) 1k, where 1k is the current for a three-phase short circuit. If, by the nature of the work, the engine does not need a high starting torque, then in these cases there is no doubt about the possibility of two-phase switching. Therefore, the possibility of starting the engine by the successive adventure of the phases of its winding to the network is the basis of the proposed device.

The novelty of the proposed device lies in the original circuit for switching on said contactor and control switch. The contactor is single-pole and single-winding, and the control switch is two-pole.

The contactor contacts are included in one phase of the line, and the winding into the second phase. The contacts of the bipolar switch are included: triggered first when turned on and last when turned off - in the third phase, and triggered second when turned on and the first when turned off - in the second phase in series with the contactor winding.

The invention is explained in the attached drawing, in Fig. 1 of which an electrical circuit of the device is shown, Fig. 2 is a longitudinal section of a switch; FIG. 3 is a section along the line MN in FIG. 2 and FIG. 4 is a section along the line KL in FIG. 2

Double pole switch

The drills are designated by the letters B and C. The letter A is the magnetic starter, in which, in addition to the disconnector E, there is a single-pole contactor q.

The inclusion of motor D is as follows. The first contact is C switch. Turning it on connects the motor phase D to the mains.

The second includes the contact B. His turn-on produces a two-phase short circuit (through the motor winding). In this case, a third phase contactor is energized, thus starting the engine.

When stopped, contact B, which is the only working contact of the drill switch, opens first. Turning it off at the same time causes the contactor q to open. Contact C is disconnected last, never breaking the current circuit.

The design of the command switch is shown in FIG. 2-4. It is made tubular. Both contacts are located on the housing axis. Contact C produces .inclusion of the first phase. Contact B produces, as described above, a two-phase short-circuit and switching on the motor by a third-phase contactor.

The working contact is in a very limited space, almost hermetically sealed. This reduces the possibility of arcing. The isolation of contacts: ensures the impossibility of transferring the arc between phases. The switch actuator is normal. Contacts

arranged so that when the contact is turned on, the c is turned on first, and when it is turned off it is turned off last. Fixed contacts are spring-loaded.

The inventor notes the following advantages of the proposed device.

1. The command switch has only one working contact and is essentially single-pole.

2. The control is performed using a standard three-core cable with a grounding conductor.

3. The single pole contactor easily fits into the magnetic starter, where simultaneously a switch for the drill circuit can be placed.

4. The switch can be easily integrated into the handle of the drill body, which will significantly reduce the weight.

5. The switch is simple in construction and easy to repair.

Subject invention

A device for remotely turning on three-phase asynchronous motors, mainly for an electric hand tool, by means of an electromagnetic contactor, which is switched on by sequentially switching on the phases of the motor winding with a control switch, characterized by

By the fact that for a single-pole and single-winding contactor the contacts are included in one phase of the line, and the winding is in the second phase, the contacts of the two-pole control switch are included: triggered first when turned on and the last when turned off - on third phase, and triggered by the second - in the second phase in series with the contactor winding.

K4 °

FIG. four