Repeat Drive Failures on Overhead cranes
Repeat Drive Failures on Overhead cranes
(OP)
I have two A.C. overhead cranes on the same runway (same power pickup). They have been in service for a number of years. The cranes are feed by a 600 volts 3 ph. supply. All axis are controlled by VFD or Vector drives.
Over the last year, I have had to replace the Bridge drives on both cranes twice. Yesterday, the drive failed a third time on one of the cranes.
The bridge drives is the only one affected. I never had problems with the hoists or trolleys. The drives are both baldor. One is controlled by an analog pendant station. the other a Cattron remote control system.
The control board is usually the one that goes on the drive. The faults I have retreived from the drives are Bus overvoltage, HW desaturation and Low init voltage.
The latest drive that failed had only been in service for approximately 2 months.It was a new drive, not only repaired.
The cranes receive moderate daily use with a few (2) near capacity lifts.
I have not done any line monitoring as I feel that any line problems would also be felt by the other drives.
Does anyone have any ideas as to the cause of such failures?
Regards
Over the last year, I have had to replace the Bridge drives on both cranes twice. Yesterday, the drive failed a third time on one of the cranes.
The bridge drives is the only one affected. I never had problems with the hoists or trolleys. The drives are both baldor. One is controlled by an analog pendant station. the other a Cattron remote control system.
The control board is usually the one that goes on the drive. The faults I have retreived from the drives are Bus overvoltage, HW desaturation and Low init voltage.
The latest drive that failed had only been in service for approximately 2 months.It was a new drive, not only repaired.
The cranes receive moderate daily use with a few (2) near capacity lifts.
I have not done any line monitoring as I feel that any line problems would also be felt by the other drives.
Does anyone have any ideas as to the cause of such failures?
Regards





RE: Repeat Drive Failures on Overhead cranes
Certainly we have to pay for innovation.
RE: Repeat Drive Failures on Overhead cranes
RE: Repeat Drive Failures on Overhead cranes
I immediatley think that you have a contact problem with the wires/bars supplying the crane. Hoist and trolley usually are supplied via cables, the bridge via naked wires and carbon brushes. A VFD does not like an unsteady grid (like bad contact produces) when working, and it results in all sorts of problems.
Why no problems with hoist and trolley? Their power is derived from the bridge power, isn't it?
Think again. Bridge usually stands still when hoisting and probably also when moving the trolley. At least the bridge isn't moving full speed in those cases.
The fact that you have got this during the last years indicate that something has happened to the wires or the contact brushes. Do a line monitoriing (onboard the bridge) and you will see what happens. Or try to inspect the brushes while running the whole stretch several times at full speed - but take care! It is a bit risky.
RE: Repeat Drive Failures on Overhead cranes
If the accel and decell are set to tight it can cause high bus voltage.
If your external braking resitor is bad it could cause high bus voltage.
If you have a operator that is trying to plug stop and the drive parameters to prevent this are not set correctly this could cause high bus voltage.
If I were to take a wild guess I would look at the resistor first to see if the years and heat have corroded the connections.
Barry1961
RE: Repeat Drive Failures on Overhead cranes
Seems like a big assumption to me. One of the first things I'd recommend is checking your power qualtiy, particularly your voltage level.
RE: Repeat Drive Failures on Overhead cranes
If the bridge travel is not too long, I would suggest a festooning system for power rather than slide bars but this is often impractical.
Given the slide bars, you will need to do some very thorough transient suppression engineering likely involving a transformer or line reactors between the slide contacts and the drive input. You may also need to add external MOV protection with much higher ratings than the drive has internally (if it has any).
A really great way to destroy a crane drive is to be lowering a load with heavy regen and be moving horizontally at the same time while encountering an intermittent open on the slide bars. You are talking pulse voltages many times higher than normal with large energy levels to complicate things further.
Crane drives are always challenging applications. Now you see why!
RE: Repeat Drive Failures on Overhead cranes
1. A second set of runway brushes in parallel with the first set. This will help prevent bumps in power continuity at runway conductor joints and so forth.
2. Each drive should have its own input inductance or universal harmonic filter which is better than an inductance.
3. For high inertia loads, punch presses, and similar demanding applications that drive needs to be oversized and then derated. Same can be said about your braking resistor.
4. I encountered and instance where the neutral point of the motor was accidentally grounded. The culprit was a conduit box connector that was contacting a ring terminal in the motor junction box. Moving the ring terminal and taping it fixed the problem.
RE: Repeat Drive Failures on Overhead cranes
A few notes.
In regards to the power pickup, The crane is fitted with a dual pickup system. Even so, I did do some monitoring and was unable to find any irregularities.
Filtering is done with inductors. I have never used harmonic filters, are they effective and are they practical on a 3 phase system?
The braking resistor suggestion is very interesting.Upon further investigation, I discovered that the internal resistor on one of the failed drive had indeed blown. I have installed a larger external resistor on the drive in question.
Thanks Again .
RE: Repeat Drive Failures on Overhead cranes
I have never used the Baldor VFD's but have used many of the servos. They have a good website with a good bit of tech info on it. They should have a chart on resistor sizing by percent braking you need.
Does the hoist rely on the internal resistor also?
Barry1961
RE: Repeat Drive Failures on Overhead cranes
I am also very surprised. The latest drive lasted approximately two months.
All the hoist drives have external resistors. Bridge and trolleys are the only ones without it.
I am still not sure why the control boards went. Hopefully Baldor will have something to add.
RE: Repeat Drive Failures on Overhead cranes
You should also consider installing an insulated green wire in the supply conduit and using that to bond the runway rails. You also need to bond the conduit for extra conductivity. The green wire should be the same size as the hot wires because of the distance that cranes usually run. You can also get devices from Erico for bonding around rail joints.
In 2005 National Electrical Code 610.61 you also have to have a redundant grounding conductor such as a runway conductor or festoon conductor in case wheel continuity fails. You still need to maintain the wheels and rails as a 2nd grounding path. Evidentally, other people had the same problem that I did or you have.
RE: Repeat Drive Failures on Overhead cranes
I have had problems with a baldor drive tripping on HW desaturation and bus overvolts when the crane driver has driven the motion into the crane buffers.
Have the drive perameters been set correctly after the first failure.
Is the drive set to coast to a stop or ramp down.
Is the drive set to plug reverse.
Are you using DC braking.
Reduce/increase the ramp down time whilst monitoring the bus volts (On the drive front, not with a meter) and a tong ammeter on the resistor cable to ensure that current is flowing to the resitor and that the bus volts are not rising to high.... (Best to increase first then slowly decrease the ramp down / deceleration time until the bus volts start to rise, then make sure that the regen circuit is clamping the bus volts via the resistor by monitoring the resistor current).
Fit a bigger regen resistor, its most likely that the muppet who priced the job has scrimped on the regen resistor.
RE: Repeat Drive Failures on Overhead cranes
I also like the reistor issues as sympomatic of the root cause. I have done plenty of bridge crane drives with sliding bar bus systems and have never experienced that as the cause of a problem like this. I agree with you that if it was, the other drives would be affected because they will get their power from the bridge, not from a separate source.
I have on the other hand seen all the things that Barry1961 mentioned above cause bridge drives to blow. If I am not mistaken, Baldor (from the old Sweo design) are one of the drives that uses the DC bus to power the control boards, as opposed to having a separate SMPS for that. This leaves the boards vulnerable to stress from repeated DC bus overvoltage, a condition that you may likely have. I too think that someone messed up by not using an external resistor on the bridge drive. That one has the most mass to stop; the bridge itself, plus the trolley, the hoist and the load! It is usually the trolley drive that does not always need an external resistor, but I always used them just in case.
"Venditori de oleum-vipera non vigere excordis populi"
RE: Repeat Drive Failures on Overhead cranes