Question about sudden motor faults.

[fredz0003]

So we had a new conveyor line installed a few months ago, it ran fine until about two weeks ago, when we get motor faults on one conveyor bed, but the overload doesn't trip, the motor is fine pulling 6.5 amps, and the overload is set for 11 amps. They people that designed the plc program, changed the signal feedback from 1 sec to 3secs but that didn't changed anything now we get like 6 to 7 motor faults on one shift, and the only way to reset it is to power down the cabinet, something tells me that it might be plc related. Any suggestions or pointer I will appreciate the help.

 

[DamianInRochester]

So we had a new conveyor line installed a few months ago, it ran fine until about two weeks ago, when we get motor faults on one conveyor bed, but the overload doesn't trip, the motor is fine pulling 6.5 amps, and the overload is set for 11 amps. They people that designed the plc program, changed the signal feedback from 1 sec to 3secs but that didn't changed anything now we get like 6 to 7 motor faults on one shift, and the only way to reset it is to power down the cabinet, something tells me that it might be plc related. Any suggestions or pointer I will appreciate the help.

It would help if you gave the specifics of what brand/model of equipment you are using. If the O/Ls are not tripped then what else is it looking at? Current sensors? GFI? Flow Sensors? etc. Since it has O/Ls I would assume there is no VFD in the equation.

 

[fredz0003]

It would help if you gave the specifics of what brand/model of equipment you are using. If the O/Ls are not tripped then what else is it looking at? Current sensors? GFI? Flow Sensors? etc. Since it has O/Ls I would assume there is no VFD in the equation.

Sorry about that, the power base is a LUB12 Telemecanique, the OL is a LUCA12FU, the coil signal is 120V, the operator said that the belt was running with nothing on it, just all of sudden the motor fault came on. I just replaced the base maybe something was wrong with the coil, crossed fingers.

 

[DamianInRochester]

Sorry about that, the power base is a LUB12 Telemecanique, the OL is a LUCA12FU, the coil signal is 120V, the operator said that the belt was running with nothing on it, just all of sudden the motor fault came on. I just replaced the base maybe something was wrong with the coil, crossed fingers.

Fred, How does the PLC detect a fault? If the O/L is not tripped as you say, then it must be looking at something else. Does it give you a more descriptive message other than generically "motor fault"?

Some things to check are:

1) IF the OL feedback was wired to the PLC as a normally close signal, then possibly the wire sourcing power to the aux contact of the OL or the wire from the OL to the PLC input is loose.

2) Do they have any kind of prox picking up gear teeth or encoder on the conveyor to measure the speed? If so, possibly one of these things is slipping or not reading reliablity from any number of reasons.

3) Are they reading back the aux of the motor contactor? Possibly they are seeing the same issue I listed with #1 with this signal instead.

4) Do you have any Photoeyes detecting product on the conveyor? If so maybe they are sensing transistions between different sections and one sensor isn't picking up properly/reliably. We do this on our conveyors to make sure we detect any jams.

5) Are they looking at the motor phases with any kind of current sensor or phase sensor to confirm that it is running? If so perhaps that needs to be adjusted or is malfunctioning.

Do you have prints? If so I would look at all the PLC inputs to determine if any of the signals could be related to the conveyor not running either directly or indirectly. Then work you way backwards.

 

[The Plc Kid]

Sounds like the Op has a MMP (Manual Motor Protector) as his base which takes the place of fuses before a contactor and has a overload for the motor.

You MMP likely has a faster interupt rating than the overload and it should have. Overloads are primarily to protect for loads that increase over time and the MMp breaker is for shorts or very fast spikes or overloads.

Sounds like your motor may be getting into a mechanical bind or something in a very fast fashion which mimics a short or very fast spike in current whic would trip your MMP before your overload as your overload typically has some small delay to it.

No different than having fused phases before a contactor and then a overload. Many times the fuse wil clear on a spike or short before the overload trips If this is happening a lot then make sure the MMP has a interupt rating close to o slightly higher than the overload. On systems like these just because they bolt together does not mean they are the right combo for the load or application someone could have selected the wrong unit. Most supplies have a part compatability matrix based on motor size and application.

Is the overload setting on the MMP adjustable? if So set it higher. In most cases the overload should be set for the FLA on the motors nameplate and not what it pulls via a amp clamp so check this also. Also on some overlaods the classic sizing it to 125% or 150% of FLA is already figured into the trip curve and reation time on some units so if your motor FLA is 8 am,ps and you set to 10 amps (125%) on some overloads that is ok and on some it is wrong it all depends on if it is already figured into the trip reaction time or not. This is info you can get from the data sheet in most cases.

If I had to guess I would say Intermittant mechanical bind somewhere.

 

[fredz0003]

Fred, How does the PLC detect a fault? If the O/L is not tripped as you say, then it must be looking at something else. Does it give you a more descriptive message other than generically "motor fault"?

To my understanding, the plc sends the input to turn on the coil, it wait 3 secs (plc program parameter), and if the motor doesn't come on before those 3 secs, it sets off the motor fault but the only indication is the red light push button, which can't reset it.

The bed is long about 40 to 50 ft, I will check Monday about in the drawings if encoders or prox are used to sense speed I know some beds use them but this one is new so I can't say yes for sure.

To answer your question about jams, we do have photoeyes but those are a different alarm and they are set to go off at 6 secs but that light is not coming on.

I must say that this long bed is used to load water bottle cases, I need to monitor for fast spikes as Plc kid mention, operator always said bed just go off on its own but I have a feeling they are overloading the whole bed with water cases, I will check for mechanical binding as well, thanks all the inputs guys, I sure appreciate your knowledge.

If the water cases causes a very fast overload or spike, maybe we need another type of power base or a different type of OL application.

 

[DickDV]

Just two corrections on the operation of normal NEMA overloads. The current setting on the overload has to be actual current without any service factor value factored in. Since different motors get different service factors per NEC code, there is not just one factor to apply. You have to multiply the actual nameplate FLA times the proper service factor and set that on the overload.

The second comment is that the time curve and the current setting are not combined. They are two separate inputs. The current setting is set by the selection of overload element or the position of a current dial. The time curve is determined by the Class of the overload block for traditional blocks and by the position of a switch on newer electronic blocks.

On traditional overload blocks, you have to select the Class when you buy the block. It can't be changed in the field. On electronic overloads, you get a selector switch for the three different time curves, 10, 20, and 30.

 

[DamianInRochester]

Sounds like the Op has a MMP (Manual Motor Protector) as his base which takes the place of fuses before a contactor and has a overload for the motor.

You MMP likely has a faster interupt rating than the overload and it should have. Overloads are primarily to protect for loads that increase over time and the MMp breaker is for shorts or very fast spikes or overloads.

Sounds like your motor may be getting into a mechanical bind or something in a very fast fashion which mimics a short or very fast spike in current whic would trip your MMP before your overload as your overload typically has some small delay to it.

No different than having fused phases before a contactor and then a overload. Many times the fuse wil clear on a spike or short before the overload trips If this is happening a lot then make sure the MMP has a interupt rating close to o slightly higher than the overload. On systems like these just because they bolt together does not mean they are the right combo for the load or application someone could have selected the wrong unit. Most supplies have a part compatability matrix based on motor size and application.

Is the overload setting on the MMP adjustable? if So set it higher. In most cases the overload should be set for the FLA on the motors nameplate and not what it pulls via a amp clamp so check this also. Also on some overlaods the classic sizing it to 125% or 150% of FLA is already figured into the trip curve and reation time on some units so if your motor FLA is 8 am,ps and you set to 10 amps (125%) on some overloads that is ok and on some it is wrong it all depends on if it is already figured into the trip reaction time or not. This is info you can get from the data sheet in most cases.

If I had to guess I would say Intermittant mechanical bind somewhere.

Whether it is tranditional overloads, a manual motor starter, or a blown fuse, I would expect that to reset the device would require a manual reset by whomever is running the machine since for safety reasons in applications like these auto reset is generally frowned upon. In that case I would have expected the OP to have mentioned that they were having to reset and overload or something similar, but instead has indicated the opposite. In this case, if they are using an auto reset device or have it set to auto reset I would highly recommend changing it not only because it might be masking your issues, but also because you run the risk of the load starting up again with no warning depending on how they have latched the circuit.

 

[hooey]

I have used these units and I think they are the same as yours and a number failed like you described where you energies the out put but the contactor would not pull in, had to replace the whole unit schnider could not say why they would some time work and not other times. get your schnider ref to replace the faulty units.

hooey

 

[fredz0003]

I have used these units and I think they are the same as yours and a number failed like you described where you energies the out put but the contactor would not pull in, had to replace the whole unit schnider could not say why they would some time work and not other times. get your schnider ref to replace the faulty units.

hooey

Yeah I replaced it yesterday I won't know for sure if that fixed the problem until Monday.

 

[JRB]

Since nothing seems to need manually reset. I would check the auxillary
contacts of the motor starter, which provide the digital input to the
plc input card proving the starter is/has closed, after a delay.
(loose connection, faulty starter aux. contacts).
If the "reset" fails to reset the motor fault error, and nothing
needs manually reset, the programming needs evaluated to see why.
Once the input condition causing the fault is cleared, the motor should
restart, after being reset.

Is the switch to start the conveyor a maintained contact?
(Is it turned off prior to resetting?)
Is the aux. contact plc input terminal connection tight?
Are the connections to the starter aux. contacts tight?
Are the aux. contacts remaining closed when the MS is on?
Loose motor starter coil neutral?
Loose plc output terminal to MS coil?
Loose OL contacts?

"Powering down the cabinet" would not reset trippable protective
devices such as the motor starter OL's, MMP, etc.

 

[Lancie1]

...it waits 3 secs (plc program parameter), and if the motor doesn't come on before those 3 secs, it sets off the motor fault.

An important question for all motor control logic is: "What is the feedback that tells you that the conveyor did not come on within 3 seconds? For a conveyor, the best method is to use a "zero-speed switch" connected to the tail-pully shaft (the one opposite of the motor-driven shaft) of the conveyor. All other feedback signals are relying on 2nd-hand information and fall to the level of "gossip" - they might be true, or might not!

For example, a signal from the motor starter contactor can show that the contactor is energized and the motor SHOULD be running, but not whether the conveyor is actually moving. The same goes for a signal from a circuit breaker overload device. This signal can show that the overload has supposedly tripped, but it does not tell you whether the conveyor is still running (which it appears to be in your case).

 

[Eric Nelson]

We still need more specifics on what exactly the PLC is monitoring to generate this 'fault' condition. It's possible that Damian's idea about the OL relay being set to auto-reset may be the issue. It may be that the PLC is simply monitoring the AUX contact, and setting the fault anytime that contact is OFF while the output to the starter is ON for more than 3 seconds.

Here's one (of many) possible scenarios:

1.) The contactor output turns on, contactor energizes, and the AUX input turns on. Motor is assumed to be running. All is well
2.) The operators overload the conveyor, and the OL relay (wired in series with the coil) trips, de-energizing the contactor. AUX is now OFF, and 3 seconds later, the fault gets latched. The fault disables the contactor output
3.) The operators quickly remove a bunch of cases, so they don't get yelled at for overloading the conveyor...
4.) Meanwhile, the OL relay automatically resets, removing all evidence of an overload...
5.) Since the fault is still present, the conveyor remains stopped

Fred says that the only way to reset the fault is to cycle power. We don't know how it's programmed, so cycling power may actually BE the only way to reset the fault...

|   Contactor  Contactor

|     Output      AUX            +-------+

|------] [--------]/[------------| TIMER |

|                                | 3 Sec.|

|                                +-------+

|

|     Timer                        Fault

|------] [-----+--------------------(  )

|              |

|     Fault    |

|------] [-----+

-Eric

 

[JesperMP]

I think we need to see the electrical diagram, and the PLC code if possible.

 

[JRB]

Even if there were other indicating conditions proving belt speed or
rotation, (prox. & flag, zero-speed switch, whirlygig) those conditional
inputs should not prevent reset and restart of the motor. And even if
the MS automatically reset its OL's, the fault should be cleared by
pushing the reset button, since the input condition causing the fault
will have automatically cleared. Neither scenario should require plc
powerdown to reset, and the programming should be evaluated to see
why.