With the continuous improvement of industrial production requirements for crane speed regulation performance, the common traditional crane speed regulation methods such as winding rotor asynchronous motor rotor series resistance speed regulation, thyristor stator voltage regulation speed regulation and cascade speed regulation have the following common disadvantages: the winding rotor asynchronous motor has collector rings and brushes, which require regular maintenance. Failures caused by collector rings and brushes are more common. In addition, the use of a large number of relays and contactors results in a large amount of on-site maintenance, a high failure rate of the speed regulation system, and poor comprehensive technical indicators of the speed regulation system, which can no longer meet the special requirements of industrial production.
The wide application of AC variable frequency speed regulation technology in the industrial sector provides a new solution for large-scale and high-quality speed regulation of cranes driven by AC asynchronous motors. It has high-performance speed regulation indicators, can use squirrel cage asynchronous motors with simple structure, reliable operation and convenient maintenance, and is efficient and energy-saving. Its peripheral control circuit is simple, the maintenance workload is small, the protection and monitoring functions are complete, and the operating reliability is greatly improved compared with the traditional AC speed regulation system. Therefore, the use of AC variable frequency speed regulation is the mainstream of the development of crane AC speed regulation technology.
After the AC variable frequency speed regulation technology is applied to cranes, compared with the traditional winding asynchronous motor rotor series resistance speed regulation system widely used in the market, it can bring the following significant economic benefits and safety and reliability:
(1) Cranes using AC variable frequency speed regulation technology have the advantage of precise positioning due to the mechanical characteristics of the motor driven by the frequency converter, and will not have the phenomenon that the motor speed changes with the load of traditional cranes, which can improve the productivity of loading and unloading operations.
(2) The variable frequency crane runs smoothly, starts and brakes smoothly, and the vibration and impact of the whole machine are significantly reduced during acceleration and deceleration during operation, which improves safety and extends the life of the mechanical parts of the crane.
(3) The mechanical brake is activated when the motor is at low speed, and the braking of the main hook and the trolley is completed by electrical braking, so the brake pad life of the mechanical brake is greatly extended and the maintenance cost is reduced.
(4) The squirrel cage asynchronous motor with simple structure and high reliability is used to replace the winding rotor asynchronous motor, avoiding the failure of the motor damage or failure to start caused by poor contact due to wear or corrosion of the collector ring and brush.
(5) The number of AC contactors is greatly reduced, and the main circuit of the motor has achieved contactless control, avoiding the burning of the contactor contacts due to frequent operation and the damage of the motor caused by the burning of the contactor contacts.
(6) The AC variable frequency speed regulation system can flexibly adjust the speed of each gear and the acceleration and deceleration time according to the on-site conditions, making the variable frequency crane flexible to operate and have good on-site adaptability.
(7) The AC variable frequency speed regulation system is a high-efficiency speed regulation system with high operating efficiency and low heat loss, so it saves a lot of electricity compared to the old speed regulation system.
(8) The frequency converter has complete protection, monitoring and self-diagnosis functions. If combined with PLC control, it can greatly improve the reliability of the variable frequency crane electronic control system.