SU609165A1 - Arrangement for induction electric motor overload protection - Google Patents

Description

one

The invention relates to the field of electrical engineering, in particular, to devices for protection against overloads of predominantly reversible, often switched on mechanisms with asynchronous electric motors.

Devices used for the same purpose are known.

For example, a device for protection of a mechanism with a synchronous motor against overload is known, containing a current relay connected via a magnetic starter contact, a protection actuation memory relay with a current protection relay contact connected in its circuit and a magnetic starter control circuit, a process completion memory relay starting the engine and the relay initial exclusion of the possibility of its operation.

A disadvantage of the known device is that it does not provide the necessary speed, does not protect the mechanism at high overload speeds and can be used only in those cases when overload does not lead to an abrupt stop of the electric motor, i.e. when the overload current rises at a significantly lower speed than the short-circuit current. For this reason, the known device cannot be used for mechanisms with rigid kinematic connections that are practically non-deformable by random obstacles.

The closest to the invention according to the technical essence and the achieved effect is a device for protecting an induction motor against overload, which contains a current relay, a protection memory relay with a current relay closing contact connected to its input circuit, a magnetic starter control circuit, a memory activation relay. motor, relay-initial exclusion protection and a resistor.

A disadvantage of the known device is its inertia and, as a result, low speed. This is due to the fact that in the event of the occurrence of appropriate conditions it is necessary to introduce protection into action as soon as possible.

faster, in the case of inertia when entering due to the occurrence of overloading, the conditions for entry may disappear and the mechanism may fail. The inertia of the known device is due to the fact that

the direct input time (hardware input time) is equal to the trip time of the contacts of the current relay when released, which is relatively long, and the response time of the memory storing relay.

The aim of the invention is to increase speed. This goal is achieved by the fact that in the proposed device the disconnecting contact of the current relay is included on the day of the winding of the initial exclusion protection relay, the disconnecting contact of the magnetic actuator is included on the input day of the engine start memory stall relay, the closing contact of the initial exclusion of the protection activating protection and parallel connected to it from the series-connected closing contacts of the current relay and the relay of remembering the fact of completion of the process The motor rammer is connected to the value of self-holding the memory relay when the engine start process is complete, its closing contact is connected in series with the said resistor and connected in parallel with the winding of the current relay, and its break contact is connected to the winding circuit of the protection tripping memory relay.

Diagram of the device shown in the drawing.

The device contains a current relay 1, included in the phase of the motor 2 through the closing contact 3 of the magnetic starter 4, a resistor 5 connected in parallel to the relay 1 through the closing contact 6, the relay 7 memorizing the fact of completion of the engine start process, the relay 8 initial exclusion protection operation at the time of the engine start, connected to the power source through the disconnecting contact 9 of the current relay 1, the relay of remembering the fact of the completion of the engine starting process, the input circuit of which consists of the disconnecting contact 10 magnet 4 th actuator, and its circuit comprises a latching relay 11 make contact 7 which is connected in series with the circuit of the switching contact 12 relay 8, in parallel with which are series-connected normally open contact 13 of the relay 7 and NO contact 14, current relay 1; relay of protection actuation 15, whose input contains a series-connected closing contact 14 of current relay 1 and a disconnecting contact 16 of relay 7, and a self-holding circuit - series-connected closing contact 17 of a relay 15 and opening contact 18, designed to remove the relay 15 from self-holding and belonging to an external (with respect to the protection device) element, for example a magnetic starter, designed to start the engine in the opposite direction; A 4-magnetic motor start starter in the working direction, in the circuit of which are connected in series the disconnecting contact 19 of relay 15 and the closing contact of the engine starting button 20 in the forward (working) direction.

The construction of the described relay-contact connections is based on the fact that

when the contact device is activated or released, the circuit made up of its parallel connected opposite contacts is briefly broken. The time of such a break is determined by the flight time of the contacts. The break time resulting from releasing the current relay is used to put the protection into operation, i.e., to de-energize relay 7. The relay-relay connections of the device relays, as it were, reverse the operation of relay 7, i.e. relay status

7 (as is the case in the prototype), and its de-energized state. This made it possible to include the closing contact 6 of the relay 7 into the resistor 5 circuit. In place of the relay 7 you can always put a magnetic starter or a contactor, the main (closing) contact of which can have practically any greater power. This removes the restriction on the application of the device in relation to the engine power of the mechanism. At the same time, the number of relays in the device remained the same.

The device works as follows.

Before starting the engine, the disconnecting contacts 9, 10 of the current relay 1 and the magnetic actuator 4 are closed, so the relays 8 and 7 are in the de-energized state. When the engine is started by button 20, the magnetic starter 4, and after it the current relay 1 is activated.

As a result, the relay 8 releases, and the relay 7 remains in the actuated state, since the time from opening the contact 12 to closing the closing contact 14 is very small (less than the release time of the relay 7). In principle, it can be equal to zero. At the time of the motor start-up, the current relay 1 releases, its closing contact in the self-holding circuit of the relay 7 is broken. Since at this moment the contact 12 is also open, and it closes only after a considerable time, the relay 11 releases and thereby remembers the fact that the engine start was completed for the entire time the engine is running (while the button 20 is closed).

After releasing the relay 7, the resistor 5 is turned off, therefore the motor current at which the relay 1 may trip decreases to the magnitude of the device response current. At the same time, contact 16 is closed in the input circuit of the relay 15. As a result, the device, having passed the starting current of the engine, is prepared for operation.

To return the relay 7 to a de-energized state, it is enough that the closing contact of the current relay 1 is open for a time equal to the release time of the relay 7. And the release time of the voltage relay is known to be significantly less than the response time.

When an overload occurs, the current relay 1 is activated and switches on the relay 15 through the input prepared by terminal 16. Triggered, the relay 15 turns off the magnetic starter 4 and goes into self-holding mode through

contact 18. As a result, the danger of overload is eliminated. Before the next engine start in the working direction, contact 18 opens. The device returns to its original state.

Claims (1)

Invention Formula A device for protection of an asynchronous motor against overload, which contains a current relay, a protection actuation relay with a current relay closing contact connected to its input circuit, a magnetic actuator control circuit, an engine start termination memory relay, an initial exclusion relay, and a resistor, characterized in that, in order to increase the speed of the device, the breaking contact of the current relay included in the winding circuit of the initial exclusion relay of the protection, the opening contact of the magnetic actuator is included in the input circuit of the motor start memory relay, the closing contact of the initial exclusion of the protection actuation and in parallel connected circuit of the series-connected short-circuit contacts of the current relay and the memory relay the fact of the completion of the engine start-up process are connected to the self-holding circuit of the relay; vigatel, its normally open contact connected in series with said resistor and connected in parallel with the relay winding current, and its NC contact is included in the relay coil circuit memorizes fact actuation protection.