Overhead travelling cranes in hoisting equipment use inverters for lifting, travelling and running with a heavy load.
These cranes can reduce the cost of construction and maintenance because they have simple structures.
Merits of inverter drives
Overhead travelling cranes with inverters have the following merits:
- Inverters can keep the load from swinging by smoothing acceleration/deceleration.
Using S-pattern acceleration/deceleration, inverters start and stop cranes more smoothly.
In addition, the vector control without sensors can support stable speed.
- Inverters can control descendent speed.
Usually, hoisting equipment has mechanical brakes to avoid increasing speed in downward operation.
However, inverters use braking resistors for this purpose.
- Inverters can detect overload.
Inverters support the following functions:
Torque limit function
Overtorque protection
- Inverters can control mechanical brakes with output toruque detection.
VFAS1 has special functions for hoist applications.
One of these functions supports mechanical brake control.
- High speed operation at light load
If VFAS1 detecs a ligh load, it automatically increases the speed by utilizing tact time reduction.
Notices regarding the use of inverter drives
- Overload trips by frequent inching operation
Frequent inching operations may cause overload trips.
When you use many inching operations within a short time, please monitor the inverter display to avoid inverter overload.
- Surge voltage of magnet contactors
Operations of magnet contactors cause surge voltage.
Therefore, please install surge reduction filters for magnet contactors.
- Contact loss of trolley wire
When overhead travelling cranes use trolley wires between inverters and motors, contact loss of trolley wires will cause inverter trips.
In this case, please replace trolley wires with cab-tire cables.
- Brake operation
VFAS1 has a special function for brake operation.
Using this brake function, inverters can control mechanical brakes with output torque dectection for added safety.
However, please adjust this function with an initial load test to assure it works reliably.
- Low speed operation
Generally motors need to reduce their output torque when operating under 30Hz.
The motors are cooled by fans mounted on their shafts, so when the motor speed decreases, the cooling efficiency also decreases.
Special motors for inverter drives don't need to reduce their output torque between 6 to 60Hz.
- Electromagnetic noise
The inverter is generating 'electromagnetic noise'.
If there are some high accuracy sensors or other sensitive equipment near the inverter drive, the inverter's noise may cause some trouble or a malfunction.
Electromagnetic noise can be avoided by installing an external noise filter or using a different wiring method.
- Harmonics
The inverter is generating 'harmonics'.
These harmonics sometimes cause a malfunction in other control equipment that is connected to the same power source.
Harmonics can be avoided by installing an external 'reactor'.
To decrease 'harmonics', we recommend to install DC reactors in all our inverter models.
(NOTE: 100V input models require AC reactors.)
Selection
In almost all cases, the capacity of the inverter is larger than the motor capacity, because hoisting equipment need high starting torque.
When inverters are installed in trolley cabinets, inverters need special modifications for vibration.
Conditions that require an inverter capacity increase
- Large starting torque over 200%.
- Short acceleration/deceleration time settings.
Application samples
Overhead travelling cranes usually use the following operating methods:
[Lifting motors]
- Vector control without sensor
- Brake functions
- Preset speed control
- High speed operation at light weight
[Traversing and running motors]
- S pattern accelertion/deceleration
- Acceleration/deceleration 1 and 2 switching
Setting table for inverters (VFAS1)
Overhead travelling cranes usually have remote control unit.
Button
Action
UP
DOWN
Lifting
LEFT
RIGHT
Traversing
FORWARD
REVERSE
Running
Title
Function
Setting range
Recommended setting
Base frequency 1
25 ot 500 Hz
52
Base frequency voltage 1
200V input model: 50 to 330 V
400V input model: 50 to 660 V
Depends on the motor
Dynamic braking selection
0 to 2
1 (Enabled)
Dynamic braking resistance
0.5 to 1000 ohm
Depends on the resistor
Dynamic braking capacity
0.01 to 600 kW
Depends on the resistor
Input terminal function selection 7 (S3)
0 to 135
20
Light-load high-speed operation selection
0 to 4
Depends on the system
Braking mode selection
0 to 3
Depends on the system
Motor rated capacity (motor name plate)
0.10 to 500.0 kW
Depends on the motor
Motor rated current (motor name plate)
0.1 to 2000 A
Depends on the motor
Motor rated rotational speed (motor name plate)
100 to 60000 min-1
Depends on the motor
Auto-tuning function (VFAS1)
After setting these parameters, please perform the following steps.
(1) Set F400(Auto-tuning 1) = 4(Motor constant auto calculation).
(2) Connect the motor wiring.
(3) Set F400 = 2(Continue operation after auto-tuning).
(4) Turn on the start signal.
