From the MotorDoc December 18 2013

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There is nothing more fun that moving a business, messing with multiple websites, transferring from older computers to Windows 8 machines (multiple… at the same time), coaching multiple female powerlifters for a meet, coordinating the publishing of a new book (dealing with contractors, marketing, evaluating the product, coordinating the release party, working with the author, etc.) and dealing with holiday traffic while maintaining the ‘day job.’  Yeah, December has been interesting so far.

Actually, it has.

The adventures have been interesting, sometimes frustrating, but I’ve picked up a few more things.  For instance, I’ve moved to a more effective website system where it is now far less time intensive than it used to be.  What took days is now dealt with in a few keystrokes – mind you, there is still the important aspect of knowing which keystrokes.

I’ve also made the leap to Windows 8.  After only two days updating, moving files, dealing with remembering passwords from ages gone, I’m down to one problem!  Wow!  After what I went through in the transition from other operating systems, this has been far easier.  Mostly it has to do with the Cloud Computing aspect – basically, I am typing on software that I am paying an annual fee for versus purchasing and installing on the computer.  By doing this I have expanded my other software systems to support imaging, video, etc.  In fact, after spending over 5 days editing and posting video from a meet held on December 8, I am finding I will now be able to do the same in about a day or two.

Marketing has been improving dramatically through the internet and social media.  If an idea is good, then in addition to the marketer getting the information out via social media such as Twitter, Facebook, LinkedIn, then others re-broadcast it.  Through early announcement of the Ernie Frantz book and the requests for stocking prices, etc. I already have an idea of how many copies have to be made on the first printing.  Not too shabby!

Technology assists us in all aspects of what we do in our daily lives and businesses, it allows us to reach out where we had not been able to in the past, search for answers, see examples, research, network, and even train from our desktops.  It also allows us to come to ruin a little faster – when things go wrong.

It is important when dealing with technology, in particular, software and electronic management systems that correct data is entered.  I have seen many programs where improper data entry has resulted in incorrect RCFA, management decisions, even loss of jobs (also related to management decisions).  Newer technologies help reduce the chance of human error, or laziness, through forced data entry directly into hand-held and scanned systems.

As I have been writing this, I discovered that the problem I ran into is well known, there is no present solution for it other than a change in strategy and how I do business.  So, what do you do?  Cut losses and make the change to how you do business.  Energy is required where it is needed, not arguing with a software giant’s disinterested support staff.

In any case, this will be the last newsletter of 2013.  With this, Merry Christmas, Happy New Year and looking forward to a shining 2014!

Sincerely,

Howard W Penrose, PhD, CMRP

What Infrared Can Tell You About Your Electric Motor

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Infrared can be used to thermally evaluate equipment. However, it requires direct contact of objects and line of sight for the system to work. In many electric motors, there are ribs between the frame and stator core which acts as an air thermal insulator. The result is that the surface temperature of the motor may be radically different than the  actual winding temperature. At the same time, bearing inner and outer races are in direct contact with the bearing housings and shaft providing more accurate  temperatures for evaluation and trending.

So far as the overall temperatures of the electric motor, there are a few temperatures that make up an electric motor’s operating temperature:

– Ambient Temperature: environmental temperature immediately around the motor. This limit, often 40C, is a limit for heat transfer from the motor.
– Temperature Rise: generated by the losses of the motor during operation and is directly related to the load of the motor. Basically, if the load rises, the temperature increases.
– Total Temperature/Operating Temperature: the combination of the ambient temperature and rise. As described, this value will vary with load.

The temperature limits for an electric motor are based upon the insulation class of the motor and bearing grease limits for the associated components. For instance:

– Class A = 105C – based upon the original oil and paper or tar and paper insulation systems
– Class B = 130C – commonly found in older standard efficient electric motors
– Class F = 155C – commonly found in energy and premium efficient electric motors
– Class H = 180C – often relates to insulation systems for high temp applications or motor repair
– Class N = 200C – high temperature applications

For motors that have service factors of 1.0, the allowable total temperature is the insulation class temperature minus 10C. For motors that have service factors of 1.15, or better, the allowable total temperature is the insulation class temperature. For example, if a motor has a Class F insulation system, a 1.0 service factor has a temperature limit of 145C and a 1.15 service factor has a temperature limit of 155C.

The temperature limits are not reflected on the surface/skin of the electric motor, as some believe, because of air gaps and the design of an electric motor to eliminate the heat generated by the losses of the motor. Different designs will generate different levels of losses and heat dissipation. The temperature limits, instead, related directly to the winding temperature of the motor. This requires either a direct line of sight of the motor windings or the motor core.

Thermal imaging has been used to identify specific point losses on an electric motor, with limited results. For instance, you have to know the loading of the motor at the time of test. Plus, in the case of totally enclosed fan cooled, or totally enclosed blower cooled, the skin temperature of the motor will vary from the fan end towards the drive end of the motor. This does allow the thermographer to identify cooling issues in these types of motors (ie: damaged fan or plugged cooling).

So, what can infrared tell us about our electric motors?

– For motors of constant load they can be used to identify ‘differences.’  However, significant temperature increases identify systems that have already failed;
– Bearing temperature by looking at the shaft and housing temperatures;
– Cooling issues;
– Severe faults;
– Can be used to determine where thermal issues are from.

In many cases, the use of just infrared technology can take significant time to evaluate or identify what is wrong and will often not provide enough detail to show how out of tolerance something is. For instance, thermal imaging may identify misalignment. However, what is good or bad? How out of tolerance is the alignment? For that you would have to perform an alignment check. Meaning – the right tool for the right job.

Does this make thermal imaging the wrong tool? No. It may be used as a system of scanning groups of equipment in order to identify gross defects which may be addressed through the application of the proper technology or inspection.

 

Consideration for Electrical Signature Analysis in Variable Frequency Drives

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For some reason, variable frequency drive driven equipment seems to carry a mystique for analysis. In truth, it just requires the user of diagnostic technologies the ability to expand the way they think when they look at data. Fault signatures and peaks are just the same as a standard motor, with the following exceptions:

– Currents should be balanced within 7% because voltage must be balanced on the output of the drive. If there are voltage related unbalances, then the drive should be evaluated, if a current unbalance exists without a voltage unbalance, then the motor and connections should be evaluated. It should be noted that the allowable current unbalance is meant for certain winding designs that are common in ‘smaller’ (less than 250hp) motors that have ‘concentric’ windings versus larger machines that have ‘lap’ windings.

– Expect very high harmonic content because of the type of voltage and current waveforms that exist. In most cases, this requires the application of filters or shaft brushes to avoid shaft currents.

– The line frequency and speeds will vary from test to test or during the same test. Evaluating and confirming the line frequency and operating speed, either through the signature or separate readings, is important as virtually all faults are related to one or the other. It is also important for when performing trending readings.

– You have to look past the electrical ‘noise’ that will exist in higher frequency data analysis to identify the issues in the system. This means knowing the fault signatures that you are looking for or practiced pattern analysis (covered in Electrical Motor Diagnostics: 2nd Edition – http://www.bookmasters.com/marktplc/10287.htm).

 

Testing Rotating Fields in the… Field!

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There is something not quite right about the way your synchronous motor or generator is operating.  An unusual vibration as it loads up that is not easily explained.  Everything is good – coupling, alignment, there was no problem with the balance in the past.

So, you check out the rotating fields with your ohmmeter and insulation resistance (Megger) tester and they pass.  They’re good, right?

Not necessarily.

There is insulation between conductors in the windings.  If the resistance across that insulation is greater than the circuit insulation, then the very small voltage in the ohmmeter will not detect it.  Unless the insulation has an issue, the insulation resistance tester will not detect a problem between conductors.  It will only tell you if the ground wall insulation is compromised.  It is so challenging that even the application of a DC voltage drop will not necessarily detect a problem.

Instead, you must use an alternating current (AC) in order to test the insulation system.

But my rotor is DC!

Doesn’t matter.  This is a test, not a method of operating the machine.  The only way to stress the insulation system to see if there is a fault is to use AC.  In fact, one of the reasons why the rotor may see the fault is there is often an AC ripple that rides long the top of DC voltage that may be, on average, 10% of the full voltage applied!  Often even more!

The best method is to use a fused 120 Vac supply and apply across the field windings.  You then take the 120 and divide by the number of fields (counting the rotating coils is the best way).  So, if I have four coils, then I should see a voltage drop of 120/4, or 30Vac.  Yes, this can be done with the fields in place, without disassembling the motor.

Before performing such a test, I recommend a few things.  First, make sure you have greater than 100 MegOhms of insulation resistance.  No point in applying an AC voltage and making yourself part of a circuit to ground.  Ouch!  In fact, making sure the rotor is grounding (as well as the stator) is a really good idea, especially if it is warm and you are sweaty.

Is this the only way?  No – you can always get a friend to do it.  They come by the dozen.

Or better yet, use an ALL-TEST IV Pro 2000 to test impedance across each coil, a PdMA MCE inductance test, or even use an SKF/Baker AWA (or similar) to compare coils a pair at a time.  Some have used the impedance test from an LCR meter, and any other instrument with an AC output and circuit comparative test result.

A combination of these tests will provide the answer you need.  In many cases, I prefer to use a low voltage test, such as my ALL-TEST IV Pro 2000, to check before applying an AC voltage.  The two combined follow my ‘use at least two technologies to confirm your finding’ rule.

Safe testing, my friends.

Considerations with On-Site Cleaning

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Great.  Testing has indicated that one of your most critical motors/generators is heavily contaminated.  You can choose to shut things down, pull the motor out, and send it in for repair or keep it running until something fails.  I mean, these are real choices, right?

Wait!  You can also have it cleaned in place!  I mean, you read that there is this dry ice cleaning thing that can fully clean your windings to perfection without damaging the winding!  Or, maybe just blowing out the winding with compressed air!  That might do it!  What could go wrong?

For the most part, field cleaning of electric motors has been around since… well… the electric motor!  However, the level of experience of field technicians varies where this very important ability exists.

There are a few things to consider, and weigh (and the list is not complete, please, share your experiences):

  1. When looking at general cleaning, non-conductive, soapy water and low pressure (less than 25 psi) air will still get to more of the windings than any other method short of steam cleaning;
  2. Many of the new ‘green’ cleaners are more ‘green’ than clean-able.  Additional hours are often needed to scrub away at things that many solvents in the past would blast right through. However, some of those things the old solvents would blast through would be the skin and the solvent would directly impact the body (kidneys, carcinogenic, etc.).  In fact, the MSDS related to the ‘green’ cleaners should also be read as, while they may be safe for the environment, it doesn’t necessarily mean it is safe for the technician, or others.
  3. Dry ice blasting can be cool (pun intended).  However, if the operator hesitates or looses focus, or is having a bad day, it will strip the insulation off of a winding faster than you can react.  Not just a warning – I’ve seen the results.  It is also ‘line of sight,’ meaning that the area directly in front of the nozzle will be cleaned.  Anything outside of the line of fire will remain exactly the way it was before.  It’s a great tool when used where it is required, but that is not everything (when you have a hammer, every screw is a nail).
  4. An oven can be assembled around a motor in the field using tarps (or other materials), heat lamps (or other heat sources) and some type of thermal control.  The heat must be ‘dry’ and temperatures must be brought up slowly.
  5. The use of a welder can also help dry out windings.  However, the insulation resistance must be high enough and an experienced technician, as well as constant vigilance, is required in order to limit the current and heat.
  6. If the motor has been flooded and there is either salty water or other contaminants, such as sewerage, in the windings, then the best solvent is water.  A non-conductive soap is generally used as well as making sure the water is warm.  Scrub brushes, an agitator for smaller motors, spray nozzle (~25 psi) can be used.  The good news, in most cases, is that water does not require an MSDS.
  7. The technicians should be fully versed in the components of the machine, electrical insulation systems, plus experience in field cleaning.  It does not matter what method is used, if there is inexperience, then there will be trouble.

While the motor is apart, additional tests can be performed before and after cleaning.  These include electrical, mechanical and visual inspections.  One challenge that can occur is that the bearings, bearing housings, mechanical components, or insulation may not pass the tests.  Unfortunately, some of the tests cannot be performed until cleaning is complete, so it is important to understand that sometimes there may be unpleasant surprises.  The good news is that pre-testing can reduce (not eliminate) these problems, such as vibration analysis, electrical signature analysis, partial discharge testing, and motor circuit analysis.

Thanksgiving Surprise!

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Yes, I was a victim on Thanksgiving!

OK, on the Wednesday before.  You see, I pulled up in line to Starbucks on my way to see a client and ordered my Vanilla Chai (yes, folks, I don’t always just drink coffee).  When I got to the drive-through window and handed over my cash the barista looked at me and said – the guy in front of you paid for your drink and said, ‘Happy Thanksgiving!’

I was stumped.  Why was that?  I mean, a kind, giving attitude should be expected from most human beings, especially around the holidays – right?  Then why should something so kind and unexpected completely take me by surprise?  I mean, the crush for shopping on Black Friday was just a few days away, and I already had people seemingly maliciously block my entry onto an extremely busy street.  I was so stunned at someone’s kindness that I realized, as I pulled away, that I should have reciprocated to the next person behind me.  I didn’t, and it drove me crazy for the rest of the day until I was able to do something for someone else.

In the USA, Thanksgiving weekend heralds the start of the Christmas season, in particular, shopping.  The time where you take your life in your hands if you are driving anywhere near a mall or major retailer.  People, for the most part, are oblivious to anyone and anything other than themselves.  Then… there is that one shining diamond in the rough.  The person with the smile and kind word that is not looking for something or some way to get something from you.  Yet, we eye them suspiciously.

It seems to be important these days, as it always has, to be ‘on your guard’ when you are away from home.  This is the time when the con-artists and thieves really are on the lookout for the unaware.

Yet, if you look at the statistics, the far greater number of our human compatriots are honest, hard working, and generally kind.  They are also out looking after their families, friends, co-workers, they are stressing over something at work, some issue at home, a rough time with their kids, their significant other, or whatever else.  The pace these days is distracting – real-time continuous contact with friends, co-workers, aquaintances, family, news (always stressful), traffic…  You get the idea.

How hard is it, really, to just take a second and buy that person behind you their Starbucks?  Or give them a smile?  Or open the door as they are carrying stuff?  Or refraining from that frustrated honk when someone is dazed at a stoplight?

It’s not all that easy, but think of the impression you will leave.

Merry Christmas and Happy Holidays!

Your MotorDoc