The following examples use frequency control of motor speed of 10 reasons to illustrate inverter application basic knowledge on the crane:
(1) the control of the motor starting current
When the motor is started directly by power frequency, it will produce a seven to eight times the motor rated current.The current value will greatly increase the electric stress of motor winding and produces heat.To reduce the service life of motor and frequency control of motor speed, start at zero speed zero voltage (can, of course, add appropriate torque).Once the relationship of frequency and voltage, frequency converter can be according to the V/F or vector control drive the work load.Using frequency control of motor speed to reduce the starting current, and improve the winding tolerance.Users the most direct benefit is the motor maintenance cost will reduce further, accordingly increase the service life of the motor.
(2) reduce the electric power line voltage fluctuation
In frequency electric mechanic starts up, the current surge voltage will be highly volatile.The range of the voltage drop will depend on the starting of the motor size and power capacity of the distribution network.Voltage drop will lead to the same power supply voltage sensitive equipment failure in the network abnormal tripping or work.Such as close to close and contactor, etc all can go wrong.And because after using frequency control of motor speed to zero frequency when the zero pressure gradually start to maximum extent, to eliminate the voltage drop.
(3) startup needs less power
Motor power is proportional to the product of current and voltage, then directly by power frequency electric consumption of power will be much higher than that of frequency conversion start needed to power.Under some conditions the distribution system has reached the highest limit and its direct start motor power frequency generated by the surge will have a significant impact on other devices with online, which will be warned by grid operators, and even a fine.If the frequency converter for motor start-stop, won't produce similar problems.
(4) the acceleration of controllable function
Frequency control of motor speed to zero speed up and according to user needs to be smooth acceleration, and the acceleration curve can also choose to (linear acceleration s-shaped or automatic acceleration).By power frequency startup connected to the motor or mechanical parts of the shaft or gear can produce severe vibration.The vibration and mechanical wear and tear will worsen, reduce the mechanical components and the life of the motor.Frequency conversion start also can be used in similar filling line in order to prevent the bottle spilled or damage.
(5) adjustable speed
Using variable frequency speed control can optimize the technological process, more and can quickly change according to the process.Can also through the PLC or other controller to achieve speed change.
(6) adjustable torque limit
Through frequency control of motor speed, can set up the corresponding torque limit to protect the machine from damage.To ensure the continuity of process and product reliability.Current frequency conversion technology makes not only the torque limit of adjustable torque even can meet the requirements of high control precision.In the condition of power frequency motor can only by measuring current value or thermal protection to control and can't like in the frequency conversion control setting precise torque values to action.
(7) a controlled stop
As controllable speed, in the frequency control of motor speed, stop mode can be controlled and have different ways can choose (dc braking deceleration parking free parking and stop).Also it can reduce the impact on the mechanical parts and motor, which makes the system more reliable, life will also be increased accordingly.
(8) and energy saving
To save energy, frequency control of motor speed in the process of starting, braking and acceleration, deceleration, small motor running current.In the case of the production condition of the same power consumption and maintenance costs than the power frequency energy saving about 20%.
(9) reversible operation control
In the inverter control to realize the reversible operation control without additional reversible control device you just need to change the output voltage phase sequence, so it can reduce maintenance costs and save installation space.
(10) to reduce mechanical transmission parts
Due to the current vector control frequency converter with synchronous motor can achieve high torque output, thereby saving gearbox and other mechanical transmission parts, eventually pose a direct variable frequency drive system which can reduce the cost and space, improve the stability.
Inverter control not only improves hoisting equipment safe operation of the time, also make the work labor intensity of maintenance maintenance cost greatly reduced, therefore, the application of variable frequency speed regulation technology in crane is to improve the work efficiency, reduce energy consumption choice to protect the safety of work.
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Inverter efficiency performance mainly in the following aspects: energy saving, improving production efficiency, speed, improve product performance improves the automation of production lines and improve the applicable environment, etc.