Common Electrical System Faults For 20 Ton Overhead Cranes

Common Electrical System Faults for 20 ton Overhead Cranes

 

The 20 ton bridge crane plays a very important role in the factory workshop. In order to ensure that it can function safely and effectively, it is necessary to scientifically carry out fault analysis and do a good job in daily maintenance and maintenance.

 

Based on this, we combined the working principle of the crane, summed up the common faults of bridge cranes and their causes, and put forward the prevention and elimination measures of the faults.

 

 

Electrical System

 

1. Fault phenomenon and cause

(1) The main motor circuit generally includes the main motor winding, the series resistance in the resistance box, the AC contactor in the control box and the linkage line, etc. Since the resistance group in the resistance box is put into operation most of the time when the crane is working normally, a large amount of heat will be generated, resulting in a higher temperature of the resistance group.

 

In a high-temperature environment, both the resistor itself and the resistor connection terminals are easily deteriorated. On the one hand, it will change the material of the resistor, which will cause the change of the resistance quality of the resistor; on the other hand, it may lead to the breakage of the connecting terminal of the resistor, so that the resistance value of the series resistor of the motor rotor or stator is unbalanced.

 

At the same time, the switching frequency of various AC contactors is particularly high during the working process of the crane, and its contacts are easily damaged and aged during frequent switching, resulting in increased contact resistance or phase loss of some contacts, causing the motor to wind The resistance value of the series resistance of the resistor is unbalanced.

 

In the above two cases, when the 20 ton overhead crane is overloaded or working for a long time, it will cause failures such as motor damage.

 

(2) The failure of the main power supply system is mainly the failure of the power supply trolley line.

 

Such as the power outage caused by the trolley line, the obvious deformation of the conduit causes the receiver to be unable to move, the side of the brush is scratched and there are granular pits on the surface, the conduit shakes too much during work, the brush wears too fast, and the electrical appliance slides greatly. Sound and shell scratches, etc.

 

The reason is often the deformation caused by improper installation of the guide rail, the stuck phenomenon caused by the thermal expansion of the high ambient temperature, the incorrect installation and positioning deviation of the receiver, etc.

 

(3) Quality problems of electronic components in the electrical system will cause damage to the main motor and other motors.

 

For example, the quality of the AC contactor is poor, the mechanical reliability is not good, the coil is hot, the suction is not good, and the coil is burned out; the quality of various protection relays is poor and damaged.

 

Some AC contactor contacts have low silver content or copper-plated iron is used for the contact copper sheet. The plastic shell of the contactor is thin or recycled plastic is used, resulting in poor contact, sparking and melting, and three-phase contact spring pressure. Unevenness and shell cracking, etc.

 

(4) The power supply voltage drops momentarily.

 

Since the power of the main motor (hoisting motor) is large (generally above 15 kW) and it starts at full voltage, if the crane installation site is far away from the power transformer or there are other relatively high-power electrical appliances on the dedicated power supply line, and the selected When the wire diameter of the power supply line is small, the power supply voltage will drop instantaneously, sometimes causing the power supply voltage drop to be greater than 10% of the rated value.

 

The reduction of the power supply voltage will inevitably lengthen the starting time of the motor or cause difficulty in starting, and will also cause damage to the motor.

 

 

Precaution

 

Regardless of the unbalanced resistance value of the series resistance of the main motor or the unbalanced three-phase voltage, the motor will have long or short, strong or weak abnormal sounds and other abnormal phenomena.

 

If the driving motor produces a high temperature rise in a short period of time, the motor will vibrate violently, and the crane may have a "powerless" phenomenon; the brake pads of the motor will collide with each other, making a high-frequency, unstable friction sound. It will cause damage to the motor.

 

At this time, the driver should stop immediately so that the maintenance workers can check and deal with it in time.

 

1. In order to prevent such accidents, regular maintenance workers should be organized to check and maintain the resistance box and control box.

 

2. Strengthen the inspection of the vulnerable parts of the power supply trolley line system, repair or replace the receiver in time.

 

3. Regularly or frequently check the status of the trolley line guide rail and shift fork, and adjust the floating suspension clamp so that the guide tube can extend freely.

 

4. Increase the thermal expansion section of the conduit, install sunshade and heat insulation board outdoors.

 

5. High-quality electrical components should be selected during maintenance to prevent the mixing of inferior products.

 

6. It is necessary to check the fixing bolts and terminals of electrical components frequently, and install spring pads or anti-vibration rubber pads.

 

7. Reasonably arrange the power supply circuit of the crane during installation, use a thicker power cord (one size thicker than the calculated value), and avoid connecting other high-power electrical equipment to the dedicated circuit.