Crane Failure and Troubleshooting 3: Electrical Equipment Article

 In the crane use process, mechanical parts, components, electrical control and hydraulic system components will be worn and lead to failure. Possible causes for the same fault are not one to one corresponding relationship. So in order to make serious analysis of fault and accurately find the real cause of the malfunction, and take elimination method corresponding to the exclusion of the fault point to restore the technical performance.

Crane electrical equipment article failure and troubleshooting

A. AC motor failure and reason:
1. The entire motor is over heat.

The causes:

• (1) JC% increase, causing overload
• (2) Working at low voltage
• (3) Motor selection is improper
• (4) Crane performance parameters have been changed after overhaul

Solving method:

• (1) Reduce the heavy degree of the crane or replace the motor with homologous JC%
• (2) When the voltage is lower than 10% rated voltage, it can stop working.
• (3) Select appropriate motor
• (4) Maintenance and keep crane design parameters

2. Stator local is overhead

The causes:

• Partial short circuit between stator silicon steel sheets

Solving method:

• Eliminate the cause of the short circuit with the insulation paint on the repair of the place

3. Stator winding local is over heat

The causes:

• (1) △/Y connection is error
• (2) Short circuit between a phase winding and the shell

Solving method:

• (1) Check and eliminate wiring errors
• (2) Repair a phase winding

4. Rotor temperature rise and stator has a large current impact, so the motor can’t reach full speed at rated load.

The causes:

• (1) The contact between the end of winding end, the neutral point or the parallel winding is poor
• (2) The contact between the winding and the slip ring is poor.
• (3) Brush instruments have poor contact
• (4) The rotor circuit has poor contact.

Solving method:

• (1) Check welding point and eliminate defects
• (2) Check connection status
• (3) Check and adjust brush instrument
• (4) Check the condition of loose and bad contact and repair; check the resistance and replace the break parts.

5. The motor vibrate at work

The causes:

• (1) Motor shaft and reducer shaft is not concentric
• (2) Bearing damage.
• (3) Rotor deformation.

Solving method:

• (1) Reinstall motor and reducer
• (2) Replace bearing
• (3) Maintenance AC motor

6. When the motor is working, it makes an abnormal sound.

The causes:

• (1) Stator phase shift
• (2) Stator core is not pressed tightly
• (3) Bearing wear
• (4) The slot wedge expand

Solving method:

• (1) Check wiring and correct
• (2) Check stator and repair
• (3) Replace bearing
• (4) Replace or saw off

7. The motor speed becomes slow after the motor is under load

The causes:

• (1) Rotor end connection has short circuit.
• (2) Rotor winding has grounding

Solving method:

• (1) Check and eliminate the phenomenon of short circuit
• (2) Check each coil and eliminate the phenomenon of short circuit

8. Friction between stator and rotor in motor operation

The causes:

• (1) Bearing wear; bearing end cover is not positive; the stator or rotor iron core deformation
• (2) The coil of the stator winding is not connected properly so that the magnetic flux is not balanced.

Solving method:

• (1) Replace the failure bearing; check the location of the end cover; clear the flying thorn on the stator or rotor core.
• (2) Check and make the coil connection correct, and the current in each phase should be equal.

9. Slip ring open circuit

The causes:

• The slip ring and brush device have dirt
• Solving method:
• Clean dirt

B. AC electromagnet failure and reason:

1. Coil is over heat

The causes:

• (1) Electromagnet suction is overload
• (2) There is a gap between the fixed part and the movable part of the magnetic flow passage.
• (3) Coil voltage is not consistent with the power grid voltage.

Solving method:

• (1) Adjust spring tension
• (2) Eliminate gap
• (3) Change coil or change the connection method

2. The sound is great when working

The causes:

• (1) Electromagnet is overload
• (2) There is dirt on the working surface of the magnetic flow path.
• (3) Magnetic system has deviation

Solving method:

• (1) Adjust spring
• (2) Clear dirt
• (3) Adjust the mechanical part of the brake and eliminate the deviation

3. It can’t overcome the spring force

The causes:

• (1) Electromagnet is overload
• (2) Main spring force is too large
• (3) Voltage is low in power network

Solving Method:

• (1) Adjust main spring force of brake
• (2) Adjust main spring force of brake
• (3) Stop work

C. AC contactor and relay failure and reason:

1. Coil heating
The causes:

• (1) Coil is overload
• (2) The activity of the magnetic flow path is not contact with the fixed part.

Solving method:

• (1) Replace the coil
• (2) Reducing the pressure of the movable contact to the fixed contact

2. Contactor hum increase

The causes:

• (1) Coil is overload
• (2) The surface of the magnetic flow path has dirt.
• (3) Blocking phenomenon in magnetic flow path automatically adjustment system

Solving method:

• (1) Reduce the touch pressure
• (2) Clear dirt
• (3) Remove jam

3. Contact heating or burning

The causes:

• (1) Contact pressure is lack
• (2) Contact has dirt

Solving method:

• (1) Adjust pressure
• (2) Clear or replace

4. The main contactor can ‘t be switched on

The causes:

• (1) The knife switch did not close, and the emergency switch did not close
• (2) Position switch is not closed.
• (3) Controller handle is not put back to zero
• (4) Control circuit fuse burn
• (5) Line has no electricity

Solving method:

• (1) Close the switch
• (2) Close the switch
• (3) Put controller handle back to zero
• (4) Inspect or replace the fuse
• (5) check the line

D. Hydraulic electromagnet failure and reason:

1. The push rod does not work after power on

The causes:

• (1) Push rod is stuck
• (2) Network voltage is less than 85% of the rated voltage.
• (3) Delay relay delay is too short
• (4) Rectifier unit does not work
• (5) Rectifier unit damage
• (6) Normally open contact of time relay doesn’t work
• (7) No oil or serious oil leakage

Solving method:

• (1) Eliminate jam
• (2) Raise voltage
• (3) Adjust the time delay relay, t = 0.5 s.
• (4) Repair or replace
• (5) Repair or replace
• (6) Maintenance contact
• (7) Repair sealing device and fill oil

2. Stroke of the push rod is small

The causes:

• (1) Oil is shortage
• (2) There is gas between the piston and the bearing.
• (3) Stroke is too small

Solving method:

• (1) Fill oil
• (2) Release gas
• (3) Appropriate adjustment

3. After the electromagnet operate, the stroke gradually decrease

The causes:

• (1) Oil cylinder has oil leakage
• (2) Toothed disc and the moving iron core valve seal is lax
• (3) The sealing ring is serious damage

Solving method:

• (1) Replace oil cylinder
• (2) Clear of mechanical impurities on the valve sheet
• (3) Replace sealing ring

4. Starting time is too long

• (1) Voltage is too low
• (2) Motion part is stuck
• (3) Brake torque is too large

Solving method:

• (1) Raise voltage
• (2) Eliminate the stuck trouble
• (3) Adjust the brake torque to the rated value

5. Braking time is too long

The causes:

• (1) Time relay contact can’t open
• (2) Motion part is stuck
• (3) Oil circuit is blockage
• (4) Mechanical partial failure

Solving method:

• (1) Maintenance contact
• (2) Eliminate the stuck trouble
• (3) Dredging oil circuit
• (4) Eliminate mechanical failure

Related information on lifting crane failure and troubleshooting

Crane Failure and Troubleshooting 1：Part Article
Crane Failure and Troubleshooting 2: Unit Article
Crane Failure and Troubleshooting 3: Electrical Equipment Article 
Crane Failure and Troubleshooting 4: Electric Control Article