RU2067346C1 - Electric motor overload protective gear - Google Patents

Abstract

FIELD: overload protection of ac motors. SUBSTANCE: overload protective gear has current transformer 11, current relay 9, start button with first make contact 14 and second one 5, first circuit connected to power supply and set up of series-connected first make contact of START button and time relay coil 8, second circuit set up of series-connected make contact of contactor whose power contacts are inserted in protected motor circuit, STOP button 7 with break contact that opens current relay contact and coil circuit of contactor 4; make contact 6 of contactor is shorted out by series-connected second make contact 5 of START button and make contact 13 of time relay 8. Novelty is that break contact 10 of current relay 9 is shorted out by make contact 12 of time relay 8 and secondary winding 11 of current transformer is connected to coil of current relay. EFFECT: improved reliability of protective gear without arcing open circuit in current transformer secondary winding. 1 dwg

Description

 The invention relates to electrical automation and can be used in control circuits of induction motors.

 A device for protecting an AC motor against overload [1] containing a power source, the elements "Start", "Stop", current transformer, current relay, time relay.

 A disadvantage of the known device is the complexity of the switching circuits of the current relay, which manifests itself in the fact that the closing contact of the time relay first (before starting the electric motor) shunts the secondary winding of the current transformer and disconnects the power supply circuit of the coil of the current relay, and after the time specified by the time relay closes the contact shunts the winding of the current transformer, and the opening contact connects the coil of the current relay to the current transformer.

This process of switching when the motor is running is accompanied by the release of energy in the form of an arc discharge on the switching contacts of the time relay, which ultimately leads to their burning, and consequently, to further breaking the secondary circuit of the current transformer and current relay, and this is prohibited in accordance with safety rules [2]
The purpose of the invention is to simplify the device by canceling the contacts of the time relay in the circuit of the current transformer of the current relay and, therefore, improving reliability.

 The goal is achieved in that in a device for protecting the motor against overload, containing a current transformer, a current relay, a start button with a first and second make contact, a first circuit connected to a power source, consisting of a first make contact of the start button connected in series and coils of a time relay, a second chain consisting of serially connected make contact of a contactor, power contacts of which are included in a circuit of a protected electric motor, a Stop button with a break contact, p the closing contact of the current relay and the contactor coil, and the contacting contactor of the contactor is shunted in series with the second closing contact of the "Start" button and the closing contact of the time relay, the closing contact of the time relay is inserted, bypassing the NC contact of the current relay, and the secondary winding of the current transformer is connected to the current relay coil .

 The drawing shows a schematic diagram of the proposed device.

 The protected motor 1 is connected to a power source 2 through contacts 3 of the contactor 4.

 The first make contact 14 of the start button is connected to the coil of the time relay 8. The second make contact 5 of the Start button and the make contact 13 of the time relay connected in series with it are bridged by make contact 6 of the contactor 4.

 The device also contains a Stop button 7, a current transformer 11, a current relay 9 with an opening contact 10, a shunted closing contact 12 of a time relay. The second make contact 5 of the start button is mechanically connected to the first contact 14 of the start button. Contacts 12 and 13 of the time relay have a deceleration upon return.

 The device operates as follows. When the "Start" button is pressed, the time relay 8 is initially turned on, which, with its make contacts 12 and 13, turns on the contactor 4, and therefore the electric motor 1.

 When you release the "Start" button, the time relay 8 is de-energized, but its contacts 12 and 13 continue to maintain their previous position during the deceleration time when returning, determined by the adjustable parameters of the time relay. The deceleration time when returning the contacts to their original position is chosen to be longer than the start time of the motor 1 from a condition that excludes the protection from falling after the start of the current to start the motor.

 Thus, during the initial start-up of the electric motor, due to the closing contact 12 of the time relay 8, by which the opening contact 10 of the current relay 9 is shunted, the contactor 4 does not turn off.

 After the deceleration time, the contacts 12 and 13 of the time relay return to the position that corresponds to the de-energized state of the relay 8 (as shown in the drawing).

 In this case, the device is prepared to protect the motor 1 from overload.

 When the motor 1 is operating, when an overload occurs, the current relay 9 is activated and through its contact 10 de-energizes the coil of the contactor 4 and the motor 1 is disconnected from the network. The time relay is energized only at the time of starting the motor 1.

 In case of failure of the time relay, its contacts 12 and 13 do not change their position, therefore, contact 13 excludes the possibility of starting the electric motor, since when the "Start" button is pressed, the contactor 4 does not turn on.

 Sources of information.

 1. Copyright certificate of the USSR N 1162006, N 02 N 7/085, 02.15.85 (prototype).

 2. Safety regulations. M. Energy Publishing House, 1986, p. 66.

Claims (1)

 A device for protecting an electric motor against overload, comprising a current transformer, a current relay, a Start button, with first and second make contacts, a first circuit connected to a power source, consisting of a first make button make contact and a time relay coil, with two NO contacts with a return delay, a second chain consisting of serially connected NO contacts of the contactor, the power contacts of which are included in the circuit of the protected motor, the “Osta” button o "with an NC contact, an NC contact of the current relay and the coil of the contactor, and the NC contact of the contactor is shunted in series with the second NO contact of the Start button and the first NO contact of the time relay, characterized in that the NC contact of the current relay is bypassed with the second NO contact of the time relay, and the secondary winding of the current transformer is connected to the coil of the current relay.