The supplier of frequency converter braking unit reminds you that with the continuous growth of demand in China's construction industry, the use of cranes has become very frequent. The application of frequency converter speed regulation technology in various transmission mechanisms of tower cranes has been in China for nearly 10 years. Although some successful application experiences have been achieved, and many frequency converter lifting mechanisms are now operating normally on construction sites, compared with other industries, the application of frequency converter speed regulation technology in tower cranes has not yet reached a mature level. However, nowadays, frequency converters have become an indispensable presence in cranes. Here are 10 reasons for using variable frequency speed regulation to illustrate the basic knowledge of using variable frequency drives in cranes:
(1) Control the starting current of the motor
When the motor is directly started through power frequency, it will generate 7 to 8 times the rated current of the motor. This current value will greatly increase the electrical stress on the motor winding and generate heat. Thus reducing the lifespan of the motor, variable frequency speed regulation can start at zero speed and zero voltage (of course, torque can be appropriately increased). Once the relationship between frequency and voltage is established, the frequency converter can drive the load to operate in V/F or vector control mode. The use of variable frequency speed regulation can fully reduce the starting current and improve the winding withstand capacity. The most direct benefit for users is that the maintenance cost of the motor will be further reduced, and the lifespan of the motor will correspondingly increase.
(2) Reduce voltage fluctuations in power lines
When the motor is started at power frequency, the voltage will fluctuate significantly while the current increases dramatically. The magnitude of voltage drop will depend on the power of the starter motor and the capacity of the distribution network. Voltage drop will cause voltage sensitive equipment in the same power supply network to malfunction, trip, or malfunction. Approaching or using contactors can result in operational errors. After adopting variable frequency speed regulation, the ability to gradually start at zero frequency and zero voltage can eliminate voltage drop to the greatest extent possible.
(3) Lower power required for startup
The power of a motor is directly proportional to the product of current and voltage, so the power consumed by a motor that starts directly through power frequency will be much higher than the power required for variable frequency starting. In some operating conditions, the power distribution system has reached its maximum limit, and the surge generated by the direct power frequency starting motor will have a serious impact on other equipment on the same network, resulting in warnings and even fines from the power grid operator. If a frequency converter is used for motor start stop, similar problems will not occur.
(4) Controllable acceleration function
Variable frequency speed regulation can start at zero speed and smoothly accelerate according to the user's needs, and its acceleration curve can also be selected (linear acceleration S-shaped acceleration or automatic acceleration). When starting through power frequency, it will cause severe vibration to the motor or connected mechanical parts such as shafts or gears. This vibration will further exacerbate mechanical wear and tear, reducing the lifespan of mechanical components and motors. In addition, variable frequency starting can also be applied to similar filling lines to prevent bottles from tipping over or being damaged.
(5) Adjustable operating speed
The use of variable frequency multi-stage speed regulation can optimize the process and quickly change according to the process. Speed changes can also be achieved through PLC or other controllers.
(6) Adjustable torque limit
After variable frequency speed regulation, corresponding torque limits can be set to protect the machinery from damage. So as to ensure the continuity of the process and the reliability of the product. The current frequency conversion technology enables not only adjustable torque limits but also high precision in torque control. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, and cannot set precise torque values to operate like in variable frequency control.
(7) Controlled stopping method
Just like controllable acceleration, in variable frequency speed regulation, the stopping mode can be controlled and there are different stopping modes to choose from (deceleration parking, free parking, deceleration parking, DC braking). Similarly, it can reduce the impact on mechanical components and motors, making the entire system more reliable and increasing its lifespan accordingly.
(8) Energy saving
Energy conservation: During the processes of starting, braking, accelerating, and decelerating with variable frequency speed regulation, the motor's operating current is low. Under the same production conditions, electricity consumption and maintenance costs are about 20% more energy-efficient than power frequency.
(9) Reversible operation control
To achieve reversible operation control in frequency converter control, there is no need for additional reversible control devices. Only the phase sequence of the output voltage needs to be changed, which can reduce maintenance costs and save installation space.
(10) Reduce mechanical transmission components
Due to the current vector control frequency converter combined with synchronous motor, efficient torque output can be achieved, thereby saving mechanical transmission components such as gearbox, and ultimately forming a direct frequency conversion transmission system, which can reduce costs and space, and improve stability.
Frequency converter control not only improves the safe operation time of lifting equipment, but also significantly reduces the maintenance cost and labor intensity. Therefore, the application of frequency converter speed regulation technology in cranes is to improve work efficiency, reduce energy consumption, and ensure work safety.