DEVICE FOR PROTECTING AN ELECTRIC MOTOR FROM OPEN-PHASE OPERATION MODES AND OVERLOADS
Asynchronous electric drive is one of the most common devices that consume electricity and are used in both industrial and agricultural enterprises. The process of operation of asynchronous electric motors is often accompanied by emergency conditions associated with current overloads, which can significantly reduce the service life and cause damage to electric motors. The fuses, circuit breakers and thermal relays used for their protection have a number of disadvantages. The authors have proposed an electronic noncontact device that protects the motor from open-phase operation modes and current overloads. The operating principle of this protection device is based on the fact that it registers the current in two supply phases and compares it with the predefined trigger threshold, which is a necessary and sufficient condition for protecting the motor from emergency operation modes. The main components of the developed electronic circuit are current transformers, rectifiers, transistorized current stabilizer, and stabilizer diode. A comparison device is an integral stabilizer chip that has an inner reference voltage source, an error amplifier and a powerful output key. The RS flip-flop is designed on logic elements. To commutate the load connected to the AC network, an electronic key is used with memory on FETs with optocoupler of power supply circuit and control circuit. The use of an electronic key allows eliminating such disadvantages of electromagnetic relays as long response time and low reliability. The developed device is made on a modern element base and is characterized by high speed, simplicity, compactness, reliability, and relatively low cost.