DEVICE FOR PROTECTING THREE-PHASE ELECTRIC MOTOR FROM EMERGENCY OPERATING MODES Russian patent published in 2023 - IPC H02H7/08 

FIELD: electrical engineering.

SUBSTANCE: invention can be used to protect three-phase electric motors operating in industry and agriculture in automatic mode with frequency control, in particular to drive sewage pumps. The technical result is to simplify the design of the protection device and increase the reliability of protection by delaying the shutdown time of an asynchronous motor with a short-term increase in temperature and taking into account the service factor, through the use of two comparators and two groups of thermistors with two operating temperature levels. The technical result is achieved by the fact that in the device for protecting a three-phase electric motor from emergency operating modes, according to the invention, transistor optocouplers and a frequency converter are introduced, and the temperature protection unit is made in the form of two comparators. The first thermistors with a positive temperature coefficient of resistance and the first operating temperature level are connected to the input of the first comparator. Second thermistors with a positive temperature coefficient of resistance and the second operating temperature level are connected to the input of the second comparator. The output of the first comparator is connected to the positive of the voltage stabilizer through the first matching resistor, the first LED and the LED of the first transistor optocoupler. The output of the second comparator through the second matching resistor, the second LED and the LED of the second transistor optocoupler is connected to the positive of the voltage stabilizer through the junction of the first transistor optocoupler. The transistors of the first transistor optocoupler and the second transistor optocoupler form a logical “AND” and are connected in series with each other, with the output relay coil and with the voltage stabilizer terminals. The opening contact of the output relay sequentially connects the neutral wire of the network with the coil of the magnetic starter and the phase wire through the “start” button, bypassed by the block with the contact of the magnetic starter and the “stop” button. The protected asynchronous motor is connected to a three-phase four-wire network through a frequency converter, power contacts of a magnetic starter and a circuit breaker.

EFFECT: simplifying the design of the protection device and increasing the reliability of protection.

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