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Unread December 2nd, 2019, 07:14 AM   #1
PLC Pie Guy
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Motor Condition Monitoring

Hey Folks.
At our plants we've been talking about monitoring the current on motors through the VFD parameters to gather a bit of historical / highest amperage draw for each drive. Were thinking of using this as a bit of a basic diagnostic watch for early signs of machine failure, weather from mechanical influences or early motor failure itself.
I can create a trend and some basic alarms, but I'm wondering if anybody knows of a bit of of code from Rockwell or is there a specific algorithm you would use to determine that a motor is drawing an abnormal amount of current and simply not reacting to an ambient condition, process change or demand increase?
What have you done to illustrate or draw attention to motors/gearboxes that might be a risk to production? Aside form vibration analysis.

Thanks
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Unread December 2nd, 2019, 07:59 AM   #2
cardosocea
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I can't speak about Rockwell code for this, but I did before put something in place to detect when belts on belt driven pumps broke by looking at torque/current within a certain speed and pressure setpoint.

Trending and having a good baseline values for regular operations is probably what is best to detect deviation from normal.
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Unread December 2nd, 2019, 08:07 AM   #3
bright676
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We do monthy and a few weekly PMs where we record the amps and on the same PM sheet is has the minimum and maximum amp per the motor name plate. When the amps start going up, its time to take a look at it.
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Unread December 2nd, 2019, 08:48 AM   #4
JesperMP
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You have to have a defined load in order to compare the trend of the current.
Easiest is if you can have a non-loaded situation, i.e. conveyors running empty.
Apart from that I dont think there is much "algorithm" to it.
I would let the SCADA handle it. Filter the data to the situation with the defined load, log the data to a long-term archive, create the trend of the data, add alarm limits to the trend - either on absolute value or increasing at a too high rate.
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Unread December 2nd, 2019, 09:29 AM   #5
tarik1978
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If you have powerflex 525/523 check this KB:PowerFlex 525 and 523 Drives, Monitoring for a Motor Overload Condition
https://rockwellautomation.custhelp....il/a_id/732074
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Unread December 2nd, 2019, 09:38 AM   #6
JesperMP
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"Motor overload" sounds more like an actually overloaded motor, i.e. being loaded beyond the nominal current.
Condition monitoring means in this topic trending for an increasing current. Increasing, but not higher then nominal current.
I might be wrong, I cannot see that Rockwell document.
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Unread December 2nd, 2019, 09:46 AM   #7
Bit_Bucket_07
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If you really want to monitor for motor degradation, I would think it very important to look at changes in current imbalance between phases.
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Unread December 2nd, 2019, 10:12 AM   #8
John Morris
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Cheaper than a VFD, and more comprehensive diagnostic features. minimum hardware and software changes to incorporate

https://literature.rockwellautomatio...m015_-en-p.pdf
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(I should probably look into this)
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Unread December 2nd, 2019, 10:39 AM   #9
thingstodo
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Quote:
Originally Posted by PLC Pie Guy View Post
Hey Folks.
At our plants we've been talking about monitoring the current on motors through the VFD parameters to gather a bit of historical / highest amperage draw for each drive. Were thinking of using this as a bit of a basic diagnostic watch for early signs of machine failure, weather from mechanical influences or early motor failure itself.
I can create a trend and some basic alarms, but I'm wondering if anybody knows of a bit of of code from Rockwell or is there a specific algorithm you would use to determine that a motor is drawing an abnormal amount of current and simply not reacting to an ambient condition, process change or demand increase?
What have you done to illustrate or draw attention to motors/gearboxes that might be a risk to production? Aside form vibration analysis.

Thanks
Summary - check if anyone will change the motor when you identify a problem. If not, put your effort elsewhere.

Motor current on across-the-line motors, for us, rises slowly over time and you can sort of tell when it might fail. We have not seen the correlation on VFDs. I think our VFDs fail on motor winding insulation failure more than heat-related issues.

More details discussing the above, if anyone is interested:

We have shown motor issues on or across-the-line motors using current, with the trend rising slowly over time. So far it has only triggered a replacement ... twice? three times? .. since we run-to-fail on most stuff under 200 HP. We just make sure that there are spares available and a plan in place to do the repair quickly. So we don't put a lot of effort into this any more.

We track bearing and stator temperatures on the larger motors (250 HP and above) and that has triggered motor changes many times.

On VFDs the voltage is adjusted, particularly in vector mode, and the current does not change a lot for belts, crushers, drags and screws depending on speed or load. Centrifugal pumps and fans show a change, but it is not the same change you see in across-the-line situations. We have not been successful in correlating motor current to imminent failure. I still collect the data, but no one looks at it.

Our Reliability guys have had much more success with vibration analysis. We lose bearings much more than anything else. Our biggest gain has been catching when a greasing PM was not actually completed even though it was signed off. Putting grease into the bearings when they need it is much more important, for us.
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Unread December 2nd, 2019, 11:56 AM   #10
GaryS
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Monitoring the motor current is well and good but the current can very under normal conditions so unless you trend it very long term it will be of limited value.
If you are looking to predict breakdowns I would look at vibration monitoring the information they provide would be much more valuable in prediction failures then motor current. Also log the start stop and total run times also the time between starts most motor failures happen when the motor starts.
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Unread December 2nd, 2019, 01:45 PM   #11
jraef
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Quote:
Originally Posted by GaryS View Post
Monitoring the motor current is well and good but the current can very under normal conditions so unless you trend it very long term it will be of limited value.
If you are looking to predict breakdowns I would look at vibration monitoring the information they provide would be much more valuable in prediction failures then motor current. Also log the start stop and total run times also the time between starts most motor failures happen when the motor starts.
I agree that monitoring current alone is not going to be that useful, because current varies with line voltage, something you can't always control. Vibration monitoring is the best method of predictive failure analysis, but requires adding vibration sensors and a way to read them (i.e. Bentley-Nevada systems) which are very expensive, so generally used only on the most critical of applications.


A low cost way of doing this is to monitor motor kW, because kW relates ONLY to the actual shaft load on the motor. Even if line voltage fluctuates, the kW stays the same under the same loading. So if you monitor kW and you monitor the WORK done by the machine, i.e. flow in a pump or fan, material weight on a conveyor, cutting speed on a machine tool, etc. etc., you can trend the two values and when the kW starts to deviate from the work performed, something is wrong. So for example in a centrifugal pump, there is a predictable relationship between flow and kW. If the kW begins to rise while flow does not, that can only mean an increase in friction, i.e. a bearing problem in the pump or motor. You will not know exactly where the problem is, but you will know there is one. On a conveyor, if you are monitoring material weight on the belt, you should have a consistent kW use based on that weight and the angle of rise, so more kW means more friction too. On a milling machine, the kW used by the motor will vary with the cutting speed for a repeatable task, so if kW starts to increase, your bit may be wearing out. Most good quality VFDs will include kW monitoring, so it's already there. For Across-the-Line motors, you can get good quality Solid State Over Load relays that provide that. Trend analysis is something you can buy in software packages if you don't want to (or can't) write your own.
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Unread December 2nd, 2019, 02:27 PM   #12
Agentbill008
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Additionally, you can monitor motor winding and bearing temperature at a specific kW. Higher temperatures in the windings and bearings can be indicative of motor failures and are easy to detect using a contact sensor or IR camera.
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Unread December 3rd, 2019, 01:00 AM   #13
janner_10
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Years ago, when I worked in a 24/7 factory, I spent months implementing something similar.

I would highlight a potential problem and plan to replace a motor.

I was always met with 'We can't afford the downtime, it works now, so don't worry about it'

It ended up being a complete waste of time and money, only to return to square one, which was wait until is breaks and run around like a headless chicken finding a replacement quick. Rinse and repeat.
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Unread December 3rd, 2019, 06:40 AM   #14
Zimmer
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Quote:
Originally Posted by janner_10 View Post
It ended up being a complete waste of time and money, only to return to square one, which was wait until is breaks and run around like a headless chicken finding a replacement quick. Rinse and repeat.
This is standard maintenance procedure, worldwide.

Have regular meetings and talk about procedures to prevent failure, sensors, monitors, thermo couples, automatic greasers etc. etc.

translates as

Replace mechanical parts only when sound from bearings etc may cause hearing damage to humans.

Replace motors when extreme heat has caused the motor paint to provide a visual indicator, preferably accompanied by smoke.
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Unread December 3rd, 2019, 07:34 AM   #15
PLC Pie Guy
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Thanks for the replies.
Just as I was originally thinking, this may not work as well as the big guys hope. This all came from originally looking at vibration analysis for early indication of failure. They decided that was to expensive and looked to me to find a solution.

I was originally concerned about the effects simply from our process affecting the current being drawn, the room temp, the product being run that day, how long since cleaning, so many variables.

Now I have some other arguments to use against me spending many many hours on current trending, but trying to convince others that its not a good solution......


Were talking better than 120 motors of all sizes and shapes and as of yet we haven't found a suitable condition monitoring and data collection tool in the vibration analysis catagory.



Our motor failures are few and far between but every time we do have a failure, it turns into this big "How can we prevent anything like this form ever happening again!!!?" situation and the then monitoring is the new panic, till the next panic comes along.. We seem to do this with many different downtime events.

Thanks folks!
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