Combined with the actual situation of industrial enterp […]
Combined with the actual situation of industrial enterprise production, based on the mathematical model of motor overcurrent protection, the inverse time overcurrent protection scheme for PLC is proposed, and the software and hardware design of the scheme is given. The motor protection performance of this program has been verified in actual production.
Large-capacity motors are used in the production of industrial enterprises. Due to the long-term continuous operation of these motors and long-term effects of dust and current changes in the production environment of the enterprise, the motor is prone to heat. If the motor does not exceed the defined calorific value, it can operate safely. If the calorific value exceeds the limit value and the motor continues to run for a long time, the motor temperature will gradually increase, resulting in lower motor performance and even burnt the motor, thus heat the motor. Protection is very important.
The reason why the motor is hot is usually caused by the current exceeding the rated value. The transient current is too high during startup, but the continuous overcurrent must be reduced within a limited time. Otherwise, the power-off circuit needs to be activated to protect the motor. That is to say, the essence of motor thermal protection is to determine the overcurrent nature of the motor.
Inverse time overcurrent protection can be understood as the protection action time varies with the motor current. There are two key points: First, the air purifier motors current exceeds the rated current for a specified time, the protection will be activated; second, the larger the motor current, the shorter the protection action time.
Experts from all over the world are studying this type of protection. The earliest use of conventional bimetal thermal relays, the inverse time overcurrent protection circuit designed by analog circuits in the 1970s and 1980s, and the powerful intelligent instruments after the 1990s. Modern enterprises are PLC-based motor protection systems.