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Motor Drive fails around every two months

02/22/2009 12:57 PM

We have a motor AC drive that failes around every two to three months, we replace with the spare and send the damaged one for repair they change a capacitor not sure what else and send it back. Again that hapense again and again. The totol motor power is not more than 5 HP. Can any help me with some answers for any reason can could cause that?

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#1

Re: Motor Drive fails around every two months

02/22/2009 1:37 PM

Are you sure that the drives current rating parameter has been set to the fla of the motor? Are all of the other motor parameters programmed correctly? Do you have the recommended air clearances around the drive? Is it mounted securely to a solid base or is there a potential for vibration?

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#2

Re: Motor Drive fails around every two months

02/22/2009 2:03 PM

Without more information it is hard to say. During testing I have found that you can degrade the life or destroy the run capacitor of a CSCR ("cap start cap run") by repeatedly turning the motor on and off or trying to start the motor when the supply voltage is low.

Can you explain what the motor is actually doing and how it is being used (is it being repeatedly cycled on and off, overloaded, etc)?

Is it being controlled by a variable speed drive or similar controller (instead of DOL ("direct on line") starting)?

Are you using power factor correction capacitor banks in your plant?

Is your supply voltage to the motor in question sagging (causing it to draw excessive current when starting)?

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#11
In reply to #2

Re: Motor Drive fails around every two months

02/23/2009 9:43 PM

We do not turn the motors (Drive) on and on always, as we turn on the motor (Unit) it runs for hours then turn off when people go fro breack. There are three motors connected to this drive, the unit is a spiral freezer, the same thing sins this unit was installed around ten years ago. Yes we are using PF in the Plant.

Thanks.

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#3

Re: Motor Drive fails around every two months

02/22/2009 3:42 PM

Need more information about the motor and the load the motor is driving.There can be any number of reasons . If you are using a 3 phase squirrel cage induction motor and is operated by a suitable starter and overload protection there is no reason for the motor to fail frequently. If the motor get over loaded the protective relay will operate if the setting is correct. Why is a condenser used ? Is it for starting of motor ( is it single phase motor?)or power factor correction? Come out with more details so that the cause of failure can be assessed.

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#4

Re: Motor Drive fails around every two months

02/22/2009 4:46 PM

What is it that is failing? Is it a drive or a motor? It is not clearly defined in your question. As V.I. Abraham has said, more data is neded for any sort of meaningful response.

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#13
In reply to #4

Re: Motor Drive fails around every two months

02/23/2009 9:49 PM

Ths Drive is failing, as mentioned by the repair company that they are replacing the capacitor

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#5

Re: Motor Drive fails around every two months

02/22/2009 11:11 PM

NNNNNN,

I assume you are talking about an AC Variable Frequency Drive failing. If not, skip to the bottom.

I would look at the ambient temperature and effectiveness of the drive´s cooling. As drive dimensions get smaller and smaller, the potential problems with heat build-up get larger and larger. I suggest you monitor the temperature where the drive is located; a simple thermometer of any type would be suitable. If heat is a problem, or if effective cooling is a problem, then your best bet would be to derate the drive´s capacity by as much as 50% and choose a drive sized for this derated capacity.

Another problem can be related to the design of the drive itself. I went through this once years ago, and replaced a pair of 150 hp drives over 6 times in a 3 month period, until the manufacturer (who had engineers visiting us on site) reported a design flaw and supplied us with upsized drives at no additional charge.

Please respond to the other posts and the questions related to confusion with the problem you are facing.

--JMM

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#14
In reply to #5

Re: Motor Drive fails around every two months

02/23/2009 9:53 PM

Surrounding temperature is around 25 °C, I have to check inside the panel during runing.

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#6

Re: Motor Drive fails around every two months

02/23/2009 2:06 AM

Find out with capacitor what else is failing.

and without knowing the basic 1ph or 3 ph difficult for us to guess.

The motor is rated for 5HP - what is the load like ? is it continuous load or some sort of shock loads.

Find the duty cycles of the drive with respect to the load that is being carried out.

and come back with more details (even if problem identified and solved)

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#7

Re: Motor Drive fails around every two months

02/23/2009 5:34 AM

I am assuming this is a single phase motor with a starting capacitor. These come in basically 2 types, a start/Run cap or a start only cap with a centrifugal switch to take it out of circuit, once the motor is up to speed.

Start/Run Type Cap motor problems

Capacitor is not of the quality needed for such usage. Replace with a top quality "Run" capacitor only of the correct value.

Motor is being started/stopped too often.

Cap start only Motor

Centrifugal switch is damaged and staying closed, keeping cap in circuit all the time. Replace the centrifugal switch.

Motor is being started/stopped too often. Replace with a Run type Cap (better quality), even though the centrifugal switch is working correctly....

I hope this helps.

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#8
In reply to #7

Re: Motor Drive fails around every two months

02/23/2009 7:38 AM

Hi Andy

It would be a 3 phase motor running of an AC drive, it sounds as thuogh some ratings are a bit on the weak side.

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#19
In reply to #8

Re: Motor Drive fails around every two months

02/24/2009 5:01 AM

He never mentions how many phases, so I assume it is a single phase motor with cap start......lets wait until he lets us in on the secret!!

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#15
In reply to #7

Re: Motor Drive fails around every two months

02/23/2009 9:56 PM

It is the drive, the motors are three phase motors.

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#24
In reply to #15

Re: Motor Drive fails around every two months

02/24/2009 8:56 AM

I think it would be most helpful if you would just identify the "drive" about which you are inquiring. Is there a nameplate on it? Copy the information on the nameplate and post it here. That should tell us a lot.

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#16
In reply to #7

Re: Motor Drive fails around every two months

02/23/2009 9:57 PM

It is the drive. The motors are three phase motors.

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#9

Re: Motor Drive fails around every two months

02/23/2009 1:49 PM

Was there anything in the system that had been changed just prior to the first time the drive started this repetitive failure problem? I know it might not be possible to track this down since it has happened repeatably and any "first change" maybe was some time ago. Some "first change" could still be causing a problem.

A colleague of mine (it wasn't me really!) made the mistake of replacing a damaged design C motor with a new design A motor, the original design C having higher start torque. It was a real problem until we figured it out! I think (but not sure) from your original post your damaged part is the VFD but my example highlights how wrong parts can get installed without our knowing.

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#10

Re: Motor Drive fails around every two months

02/23/2009 6:31 PM

Static will cause this type of failure. Look for a missing or wimpy ground especially if the system has plastic conduit. The motor will run fine without a ground, but the static protection for the semiconductors won't work.

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#12

Re: Motor Drive fails around every two months

02/23/2009 9:45 PM

We do not turn the motors (Drive) on and on always, as we turn on the motor (Unit) it runs for hours then turn off when people go fro breack. There are three motors connected to this drive, the unit is a spiral freezer, the same thing sins this unit was installed around ten years ago. Yes we are using PF in the Plant.

Thanks.

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#17

Re: Motor Drive fails around every two months

02/23/2009 10:41 PM

Running three motors on one VFD can be a problem.

I have seen where when one motor is in an overhauling condition and the others are not, a VFD can do some strange things and blowing capacitors is one of them. Change the drive to one that can handle a regenerative current from a motor and try that.

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#18
In reply to #17

Re: Motor Drive fails around every two months

02/24/2009 4:11 AM

I have successfully ran multiple motors on an ABB ACH550 drive. As long as the drive is sized to the total load it works just fine.

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#23
In reply to #18

Re: Motor Drive fails around every two months

02/24/2009 8:46 AM

As have I. However, spiral freezers can have unbalanced loading of product causing one motor to overhaul.

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#21
In reply to #17

Re: Motor Drive fails around every two months

02/24/2009 7:20 AM

We do have more than one drive, we use the next as we send the damaged one for repair. Looking into the tech. repair report finding that the change was "Defected Capacitors" and "Power Module Defective"

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#25
In reply to #21

Re: Motor Drive fails around every two months

02/24/2009 1:29 PM

Oh, so its the drive capacitors and power module failing. It is hard to say why the drive electronics are failing. I have seen capacitor failure due to vibration (but that is quite rare).

Is your motor drive subject to regular vibration?

Failure of the power module is generally due to overloading of the output or power quality issues (such as repeated sags or low supply voltage) which can cause the drive to draw more current to supply the same power (overstressing the components). Another common cause of both capacitor and drive module failure is overheating due to blocked or restricted air flow over the drive's heatsink. I have also seen drives fail because too many motors have been connected up to the drive and exceeded its output power rating.

Have you checked that the drive is not overheating?

It does depend a little on what brand drive you are using (what is the brand and model you are using?)

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#20

Re: Motor Drive fails around every two months

02/24/2009 6:08 AM

Is the drive being fed by a single phase source? I have seen issues with a single phase drive not being properly sized for the application. Many small drives can output 3 phase to motors from a single phase source but the drive is usually heavily derated.

Shawn

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#22

Re: Motor Drive fails around every two months

02/24/2009 8:09 AM

Its 3 phase, so my comments were not that valid.....other than cap quality maybe questionable!!

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#26

Re: Motor Drive fails around every two months

02/24/2009 9:14 PM

Do you have schematic diagrams of the drive and are you interested in doing component level repairs?

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#27
In reply to #26

Re: Motor Drive fails around every two months

02/24/2009 11:43 PM

No, we do not repair it in house, we just send it out, we are just looking for the root cause.

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#28

Re: Motor Drive fails around every two months

02/26/2009 10:03 PM

Thank you All.

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#29

Re: Motor Drive fails around every two months

02/27/2009 12:57 AM

?

Problem resolved ? What was it ?

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Users who posted comments:

Andy Germany (3); Anonymous Poster (8); DaveB (1); garth (1); jack of all trades (2); jmueller (1); LG_Dave (1); NNNNNN (1); North of 60 (3); Ricky T (2); sb (2); Shawn33 (1); TD Starman (1); The Commoner (1); V.I.Abraham (1)

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