Application case |

Application of frequency converter in grab crane modification

1. Introduction

Bridge cranes are hoisting equipment widely used in industrial production. With the continuous improvement of industrial production requirements for crane speed regulation performance, the traditional crane speed regulation method (mainly wound asynchronous motor rotor string resistance speed regulation system) requires on-site maintenance. Large, the failure rate of the speed control system is high, and the comprehensive technical indicators of the speed control system are poor, and it can no longer meet the special requirements of industrial production. Therefore, frequency converters have been widely used in the lifting industry, improved production efficiency, and have been well received by users.

2. Operation status of traditional bridge crane 

The traditional electric drag system mainly includes a lifting mechanism (main lifting and auxiliary lifting of the hook) and a translation mechanism (cart, trolley). Generally, the YZR winding AC asynchronous motor rotor circuit is used for speed regulation by series resistors in the rotor circuit and is controlled by a cam. controller, relay, contactor control. The following problems exist in actual operation:

1) The lifting mechanism and translation mechanism drag operation system adopts rheostat speed regulation, which has poor operating performance, and the resistance elements are burned out and broken from time to time.

2) Energy-consuming slip speed regulation has high energy consumption, soft mechanical properties, small speed regulation range, and poor smoothness.

3) The smoothness of speed regulation is poor, and the mechanical impact on the reducer, coupling, and wire rope is large, affecting the service life.

4) The relay and contactor control system switches frequently, and the inrush current is large during starting. Therefore, contact burnout and motor burnout faults occur from time to time, and the failure rate is high.

3. Frequency conversion speed regulation transformation plan

In view of the above problems of traditional cranes, the customer requested technical transformation of the hook lifting electric drag system and the large and trolley electric drag system of the bridge crane. In order to overcome the shortcomings of the winding motor series resistance speed regulation system, variable frequency regulation was adopted. Rapid technology transformation of crane transmission system.

4. Transformation examples

Transformed with a special frequency converter for lifting.

The special frequency converter for lifting is designed for applications in the lifting industry and meets relevant national standards. The hardware adopts a motor-specific control chip, is equipped with low-power IGBT, and has built-in lifting-specific software. It has strong overload capability, high starting torque, and anti-slip hook functions. Stable working conditions and good mechanical properties can be obtained by using vector control. While meeting impact load and heavy-load applications, it can also perfectly present the process control characteristics of the lifting industry, improve system efficiency, and meet the requirements of rapid response, smooth and safe operation.

The torque control performance ensures safety, reliability and efficiency in lifting and hoisting industries. It can be used for AC stepless speed regulation of hoisting, pitching, luffing, cart, trolley, slewing, grab and other mechanisms of various cranes.

5. Application effect after transformation

1) The process of starting, braking, acceleration, and deceleration of the crane is smoother and faster, and the positioning is more accurate. The vibration and impact of the entire machine during acceleration and deceleration during operation are significantly reduced, reducing load fluctuations, and safety is greatly improved.

2) Since the starting current of the motor is limited, the heat consumption of the motor is reduced during frequent starts and stops, and the service life is extended.

3) The electromagnetic brake operates at low speed, and the wear of the brake skin is very small, and the service life is extended.

4) The variable frequency speed control system can flexibly adjust the speed and acceleration and deceleration time of each gear according to the on-site conditions, making the variable frequency crane flexible in operation and good on-site adaptability.

5) Save energy, the motor has small operating current, high operating efficiency and small heating loss. The measured energy saving in this case can reach about 30%. Under the same production conditions, power consumption and maintenance costs are saved by about 20% compared with before the restructuring.

6) High reliability: The frequency converter has a built-in anti-slip hook program and complete protection, monitoring and self-diagnosis functions. If combined with PLC control and the use of a closed-loop vector control cabinet, the reliability of the electronic control system of the frequency conversion crane can be greatly improved.

7) Efficient operation: The crane can operate at 3 times speed when the hook is empty or under light load, improving loading and unloading efficiency.