Motor burned out two times

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Hi guys

I am looking for a bit of input on an issue i have had the last couple of days. There is an oil fryer in the plant which has a couple of belts in it. The first belt is a non stick teflon short belt on the infeed which is driven by a stainless steel enclosed motor. The motor was running fine until the production changed onto a different product (a salt and chilli product) and after an hour or so it stopped driving the conveyor. The motor is run on an inverter and is switched on and off through a HMI screen and all of those were ok, no faults and no issues with the mechanics of the shafts, conveyor etc. The conveyor is submersed in the oil at a temperatur of 180c. Nothing has changed on the whole system and the motor and inverter are properly rated and everything else in the fryer is as it should be. I swapped out the motor out with a spare at the end of the day (same stainless steel motor) and ran it and it was all ok. Voltages, current, and loads all ok when measured with meter. The spare motor ran for 2 days after i changed it and there was no problems. But the same thing happened again tonight after and hour when they went back on to the salt and chilli recipe. I wasnt there to witness what happened but they told me over the phone the motor has stopped the same way it did and when they opened the panel there were no trips or the inverter wasnt showing any errors. I wont be able to look at this until the morning but i am wondering is there something in this recipe causing this to happen. I am at a bit of a loss on this . FYI the stuff going through the fryer is chicken breast covered in this salt and chilli flavour.

This may sound silly but i am wondering is there salt and chilli conducting in the oil and heating up more, or would it be doing something to the conveyor in the oil which is causing the motor to overheat? Any input or experience.
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
Possibly the ambient temperature of the new recipe has increased, it may warrant a look at the motor protection, O/L's etc, they should be operating in the case of an overload, in some cases the O/L is at the bottom of the contactor and may be a little high.
Although you mentioned an invertor, (VFD?), these usually have a peak current setting that maybe should be looked at,.
Has there been an autopsy on the failed motor to see if it is actually fried?
Max.
 

SamR

Joined Mar 19, 2019
5,060
is there salt and chilli conducting in the oil and heating up more
Oil should be non-ionic so the salt is not dissolving and ionizing in it so no. Any water in the chicken that would ionize with salt is vaporized. The oil temp control should not be affected. I don't understand what that has to do with the motor? I hate to say it but seems coincidental?
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Hi guys

Yes Max the motor is run on a VFD. The motor itself runs hot as in it gets up to 60 degrees c but it is rated for this and is what it normally runs at. I am wondering did it just get too hot and maybe if i test it tomorrow when it is cooled down fully and the fryer will be clean and empty will it run. The motor that stopped working the other day is with the motor rewind repair guys but i wont hear from them until tomorrow regarding what happened to it. I have a spare motor which i will test the windings against the one on the machine and see what the difference is. I am just puzzled as to why only on this recipe twice in 3 days
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
The motor would normally show FLA (full load amps) and this is what the VFD and/or any O/L protection should be set for.
Usually VFD's can be set to display many conditions, amperage for one, if this is possible then it may mean taking periodic readings during the process, a little tedious, but often the way to zero in on the problem.
Testing and comparing the windings by resistance value of a defective motor , unfortunately will not tell you anything usually.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
A shorted turn on an AC induction motor is enough to disable it, but the fraction of an ohm difference between the two is indistinguishable as far a resistance reading is concerned.
An AC motor is an inductive device, so winding resistance is not a sure indication, if the winding shorted to ground, then that would be another matter and more definitive.
Max.
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Hi guys

So checked the fryer out this morning and seen that there had been solid pieces of chicken jammed underneath the conveyor which in turn had jammed the drive chain. I repaired the chain and checked over everything. The motor current is rated for .9Amps and the max current rating on the inverter is set for 1 amp. I have had the belt running the last hour and the current is staying level at .65 amps. I have attached 3 photos of the last three faults logged on the inverter. The first pic is the last alarm of under voltage but this is what happens when you drop power to it which is a normal alarm as i got the guys to power the panel down last night. The second pic is of the alarm which i am assuming would have been the chain jamming which stopped the motor running yet it did not have any errors on the HMI screen or on the inverter itself. The third photo is of the motor which i again assumed burned out and went to earth. Although the inverter captured it in the log it again did not show up on the HMI screen as a fault. I am suspecting there is an issue with the communications from this drive to the HMI. Even though the inverter is doing its job and its setpoints are correct the HMI doesnt seem to be capturing this data.

When i trip the circuit breaker F2 from the 4th pic the HMI screen shows an alarm then. I have attached the last pic of the drawing of the conveyor wiring. I don't see any sort of feedback signal to say inverter running/healthy or alarmed or am i missing something?

Just to update i ran the belt and changed the max current settings from 1amp to .35 amps to set up a false alarm and it actually flagged up an error message on the HMI screen but it didn't stop the drive??
 

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If the motor is running at low speeds, it may not have enough cooling.
Specialty VFD-type electric motors have a separate cooling fan if they must spin slow at full power. I suspect the new recipe needs higher torque at lower speeds. I wonder if you can change the gearing.
The VFD should have a torque-limit, motor overload % and current-limit programmed to protect the motor.
 
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