How To Buy A Frequency Conversion Crane
Apr 10, 2023
How To Buy A Frequency Conversion Crane
The frequency conversion crane is the most promising one among the speed regulation methods of asynchronous motors.
Frequency conversion cranes use frequency conversion speed regulation (change the speed of the motor by changing the frequency of the motor power supply) to have a large speed regulation range and high smoothness. When the frequency is changed, the applied voltage of the stator is changed at the same time, which can realize constant power or constant torque speed regulation to adapt to different cranes. The requirements of the load, the static difference rate of the characteristic at low speed is high, the efficiency and power factor of the speed regulation are high, and it is the most promising one in the speed regulation method of the asynchronous motor.
Crane speed control technology has a long history of development, from DC speed control to AC speed control, from AC stator speed control technology to DC thyristor speed control device, and then developed to the widely used rotor series resistance speed control technology today.
However, these technologies have many shortcomings such as fragile components, inconvenient maintenance, large equipment impact, and small speed regulation range.
Since the 1990s, frequency conversion speed regulation technology has become more and more mature, and it has been widely used in the lifting field due to its advantages such as large speed regulation range, simple structure, convenient maintenance, noise reduction, and power saving.
1. Lifting mechanism
A general large-tonnage crane has two independently driven hoisting mechanisms, and each hoisting mechanism is synchronously driven by two motors to rotate its own wire rope reel, and then the hook is lifted through the multi-stage deceleration of the movable pulley block.
The frequency conversion and speed regulation transmission scheme of the hoisting mechanism adopts a "one drive one" scheme with one frequency converter and one motor. In order to improve the dynamic characteristics and high torque output capacity of low-speed transmission, each motor adopts a Speed closed-loop control.
There is a master-slave control scheme with power balance and speed synchronous control functions between the 2 frequency converters of each hoisting mechanism. These control schemes can realize the precise torque balance distribution of the 2 motors and the speed synchronization of the 2 hoisting mechanisms.
2. Translation mechanism
The translation mechanism of the crane is divided into a cart mechanism and a trolley mechanism, and the two mechanisms generally use multiple motor drive schemes.
The electronic thermal relay protection function provided by the frequency converter cannot realize the overload protection of a single motor. Therefore, a low-voltage circuit breaker with thermal overload protection function is connected in series in each motor circuit to realize the overload protection of a single motor. The motor fault signal is taken from the auxiliary contact of the low voltage circuit breaker.
