Frequency Control Program of Mono Overhead Cranes

Frequency Control Program of Mono Overhead Cranes

Mono overhead cranes use dedicated conic motors for lifting. Vibration there is great with frequent operation. Inrush current is also great. Terminals of contactors are often burnt due to inrush current in the motor, which increases maintenance amount and costs and results in great production loss. Therefore, it is a must to transform frequency control.

Electric transmission system of cranes consists of lifting motor (main hook motor), large and small motors. They are divided into dual-beam ones and single beam ones. Dual-beam cranes usually adopt AC rotor motors and takes advantages of rotor resistance for start-up and speed regulation. Vibration there is great with frequent operation. Inrush current is also great. Terminals of contactors in the electric transmission are often burnt due to inrush current in the motor, which increases maintenance amount and costs and results in great production loss. Therefore, it is a must to transform frequency control. Take mono overhead cranes of a factory in Xingtai, Hebei for example. Lifting weight of their cranes is 5 tons. Workshop environment is very tough. A lot of processes need to be done by cranes. Operation of cranes is quite frequent. Original electric transmission system uses contactors to control. Its maintenance is frequent, affecting production.

Implement scheme:

A main hook motor of 7.5KW. Adopts C320-4T0011G inverter (vector type, frequency mechanism has to adopt high torque vector inverters foe stable operation).

Two large crane motors of 1.1KW. Adopt E380-4T0037G inverters (general type, an inverter with two motors).

A small crane motor of 0.8KW. Adopt E380-4T0015G inverters (general type).

Due to the special structure of conic motor where an end is an output bearing and the other is a brake flange connected by the spring; brake flange is pushed out by the spring driven by the input voltage in motor operation.

(1)  Acceleration to start the motor should be fast. If it is too slow, motor rotor speed is not high enough to open the brake flange and motor bearing cover may be broken.

(2)  Set lower frequency limit as high as possible. If motor frequency is lower than 30HZ, brake flange may not be open and motor bearing cover may be broken.

(3)  Shutdown mode should be free because motor is shut down by the abrasion of brake flange. Don’t use electrical deceleration to shut down.

(4) Cranes are running in the three-dimensional space. Inverters are required to be installed on the cabinet near the crane main power box. Mechanical vibration is obvious in operation. Therefore, anti-vibration pads should be installed to prevent vibration affecting the performances of inverters.

Transformation of electrical lines:

Original electrical system is controlled directly and reversing by contactors. Power boxes of the hooks and small cranes are controlled by the large crane power box through main contactors. Hook and small crane motor share the main breaker for protection. Large crane motor owns a breaker for protection. A small crane breaker is added to the main power box. Since positive and negative inversion is realized by external control of inverters, only three wires are required to be output to hook stoppers. In the transformed program, hook motor wires are connected to the stopper. It does some changes to the wiring of the stopper. A wire connecting to the small crane motor and breaker in the main power box is rearranged. Another six-core control wire is connected to the control box. Original 6 contactors are replaced by a relay whose coil voltage is 36V. The relay provides only dry contacts. Positive and negative inversion is interlocked on the relay. Original control circuit changes little. Positive and negative signals are sent to inverters by the relay. Signal source is given by a CM port of the inverter.

Parameter settings of main C320 vector inverters:

F0.0:  1  sensorless vector control

F0.1:  0  digital settings of frequency selection

F0.2:  50  frequency digital settings

F0.4:  0001  external port control

F0.7:  30   lower frequency

F0.8:  50  upper frequency

F0.10: 0.5   acceleration time

F1.15: 380  rated voltage of load motor

F1.16: 50   rated frequency of load motor

F1.17: 15.6 rated current of load motor

F1.18: 1460 rated speed of load motor

F4.3:  1    free parking

Set F1.20 to 1 before first testing the machine for self-determination on parameters to get internal parameters of motors.

Parameter settings of E380 general inverters of large and small cranes are as follows:

F0.0:  0000   general mode               

F0.1:  0  digital settings of frequency selection

F0.2:  50  frequency digital settings

F0.4:  0001  external port control

F0.7:  25  lower frequency

F0.8:  50  upper frequency

F0.10: 0.5   acceleration time

F4.3:  1    free parking

Having been tested for a time after transformation, crane motor controlled by inverters can satisfy production requirements and has following features:

1. The function of soft start and soft stop reduces mechanical transmission and improves performances of steel structure significantly.
2. It has fast dynamic response without any gliding hook and realizes the function of zero crossing.

3. Highly integrated components and high reliable low-voltage electrical appliances effectively reduces the probability of system failure.

4. It has functions of self-test and alarming and reduces maintenance time and costs significantly.