Chapter 3/5: 4 Common Problems and
Troubleshooting Methods for Crane
Electrical Systems
Zora Zhao
Crane OEM expert.Overhead / Bridge / EOT Crane, Gantry Crane, Jib Crane
and Crane Spares
Published Feb 4, 2021
I. AC motor failure and cause condition
1. Uniform overheating of the whole motor
Failure causes.
1. The connection rate (JC%) is increased, causing overload
2. Working under low voltage
3. Improper motor selection
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4. Change the crane performance parameters after overhaul
Exclusion method.
1. Reduce the crane heavy degree or replace JC% corresponding motor
2. The voltage is lower than 10% of the rated voltage, stop working
3. Choose a suitable motor
4. Maintain the design parameters of the crane after maintenance
2. Stator local overheating
Cause of failure: Local short circuit between stator silicon steel pieces
Exclusion method: Eliminate the cause of short circuit, use insulating paint to wipe in
the place of repair.
3. Stator winding local overheating
Cause of failure.
1. Wiring error.
2. A phase of the winding in two places, and shell short circuit
Removal method.
1. Check and exclude wiring errors
2. Repair a phase winding
4. The rotor temperature rises, the stator has a large current shock, the motor cannot reach full
speed at rated load
Cause of failure.
1. Poor contact between winding end, neutral point, or parallel winding.
2. Poor contact between winding and slip ring.
3. Bad contact in brush equipment.
4. The rotor circuit has poor contact.
Exclusion methods.
1. Check the welding place, eliminate the defect.
2. Check the connection condition.
3. Check and adjust the brush equipment
4. Check the loose and poor contact and repair; check the resistance and replace it if broken.
5. The motor vibrates when working
Cause of failure.
1. The motor shaft and reducer shaft are concentric.
2. Bearing damage and wear.
3. Rotor deformation.
Exclusion method.
1. Reinstallation of alignment
2. Replace the bearing
3. Overhaul the AC motor
6. Unusual sound when the motor is working
Cause of failure.
1. Stator phase misshift
2. The stator core is not pressed tightly
3. Bearing wear and tear
4. Slot wedge expansion.
Elimination method.
1. Check the wiring and correct
2. Check the stator and repair
3. Replace the bearing
4. Saw off the swollen wedge or replace it.
7. Motor rotates slowly after bearing load
Cause of failure.
1. Short circuit at the rotor end connection
2. There are two grounded rotor windings
Elimination method.
1. Check and eliminate the short-circuit phenomenon
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2. Check each turn of the coil, repair the broken circuit and eliminate the short circuit
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8. Friction between stator and rotor during motor operation
Cause of failure.
1. Bearing wear, bearing end cover is not correct, stator or rotor iron core deformation
2. Incorrect connection of stator winding coils, so that the magnetic flux is not balanced
Removal methods.
1. Reason to replace the failed bearing; repair the position of the end cap; clear the stator or
rotor core on the fly spike
2. Check and make the coil wiring correct, measure the current in each phase should be equal.
9. Sparking on the brush or burned slip ring when the motor is working
Cause of failure.
1. The brush is not well ground
2. The brush is too loose in the brush grip
3. Dirty brush and slip ring
4. The slip ring is not flat, causing the brush to jump
5. Insufficient brush pressure
6. The brush grade is not correct
7. The uneven current distribution between brushes
Exclusion methods.
1. Ground the brushes
2. Adjust the brush or grind suitable
3. Wipe the slip ring clean with alcohol
4. Turn and polish the slip ring
5. Adjust the brush pressure (18 ~ 20kPa)
6. Replacement
7. Check the brush frame feed line and brush, and correct
10. Slip ring open circuit
Cause of failure: slip ring and brush equipment dirty
Removal method: clean dirt and scale
II. The AC solenoid failure and the cause of the situation
1. Coil overheating
Failure causes.
1. Solenoid suction overload
2. The gap exists between the fixed part of the magnetic circuit and the movable part
3. Coil voltage and grid voltage does not match
Exclusion method.
1. Adjust the spring tension
2. Eliminate intermittent
3. Replace the coil, or change the connection method
2. Loud sound when working
Cause of failure.
1. Solenoid overload
2. Dirt on the working surface of the magnet flow circuit
3. Magnetic system skew
Removal method:
1. Adjust the spring
2. Eliminate the dirt
3. Adjust the mechanical part of the brake to eliminate skewing
3. Can not overcome the spring force
Cause of failure.
1. Solenoid overload
2. Excessive main spring force
3. Low voltage in the grid
Exclusion method.
1. Adjust the spring
2. Adjust the main spring force of the brake
3. Suspension of work
III. The AC contactor and relay failure and cause condition
1. Coil heating
Failure causes.
1. Coil overload
2. The magnetic flow circuit of the activity of contact, not a fixed part
Exclusion methods.
1. Reduce the pressure of the movable contact on the fixed contact
2. Eliminate deflection, jamming, dirt, or replace the coil
2. Contactor buzzing sound increased
Cause of failure.
1. Coil overload
2. Dirt on the surface of the magnetic flow path
3. Magnetic path automatic adjustment system in the jamming phenomenon.
Exclusion methods.
1. Reduce the small contact pressure
2. Eliminate the dirt
3. Eliminate the jam
3. Contact heat or burned, burned out
Failure causes.
1. Insufficient contact pressure
2. Dirty contacts
Removal method.
1. Adjust the pressure
2. Exclude or replace
4. The main contactor can not be connected
Cause of failure.
1. The gate switch is not closed, the emergency switch is not closed
2. The warehouse switch is not on
3. The controller handle is not put back to the zero position
4. Control circuit fuse burned out
5. No power in the line
Exclusion method.
1. Close the switch
2. Close the switch
3. Handle back to zero
4. Check or replace the fuse
5. Check the line for voltage
5. Crane operation often fall off the switch
Failure causes.
1. Insufficient contact pressure
2. Contact burning
3. Dirty contacts
4. Overload operation, resulting in excessive current
5. Slip wire parallel, collector, and slip wire poor contact
Exclusion methods.
1. Adjust contact pressure
2. Replace the contacts or grinding repair
3. Cleaning
4. Reduce the load
5. Repair the track or trench sliding contact line
IV. The hydraulic solenoid failure and cause condition
1. The push rod does not move after the power is applied
Failure causes.
1. Pushrod jammed
2. Network voltage is lower than 85% of the rated voltage
3. Delay relay (ZLO silicon rectifier on) delay time is too short
4. The rectifier does not operate
5. Rectifier device damage
6. Time relay normally open contacts do not operate
7. No oil or serious oil leakage
Exclusion method.
1. Eliminate the jam
2. Increase the voltage
3. Adjust the time delay relay, t delay ≈ 0.5s
4. Repair or replace
5. Repair or replace
6. Overhaul the contacts
7. Repair the sealing device and make up the oil
2. Push rod stroke small
Cause of failure.
1. Insufficient oil quantity
2. The gas between piston and bearing
3. The stroke is too small
Elimination method.
1. Replenish the oil quantity
2. Discharge gas
3. Proper adjustment
3. After the solenoid works, the stroke gradually decreases
Cause of failure.
1. Oil leakage from the cylinder
2. The toothed valve piece and dynamic iron spool valve piece seal is not tight
3. Serious damage to the seal
Elimination method.
1. Replace the cylinder
2. Clear the mechanical impurities on the valve
3. Replace the seal ring
4. Start time is too long
Failure causes.
1. Low voltage
2. Moving part jammed
3. Brake braking torque is too large
Elimination method.
1. Increase the voltage
2. Exclude jamming fault
3. Adjust the braking torque to the rated value
5. Braking time is too long
Cause of failure.
1. Time relay contact can not open
2. Moving part jammed
3. Oil circuit blockage
4. Mechanical part failure
Removal method.
1. Overhaul the contacts
2. Exclude the jam
3. Unclogging the oil circuit
4. Eliminate mechanical failure
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