The Technical & People Approach
Introduction Electrical equipment failures especially motors account for nearly half of facilities downtime, and the difference between a poor Electrical Preventative Maintenance Program and an excellent one is approximately 12 times in failure rate.
Failure rates from 1983 Electric Power Research Institute (EPRI) project performed by General Electric (GE) where 4797 motors were evaluated with 1227 failures, state failure rates range from 9.3% to 0.8% with an average of 3.4% per annum.
My experience as a Motor Analyst suggests this is similar to all Electrical Assets (Circuit Breakers, Inverters, Isolators, Cables and Terminations etc).
Even at the average a facility with 500 motors will experience a failure every 21 days which if critical will take your plant down. That downtime normally is a dominant cost in the total cost of ownership, often forgotten.
An Electrical Preventative Maintenance Program is considered excellent if the failure rates are less than 1%, that's one failure every 2 months in our example.
Best Practice Motor Management has proven track record of achieving failure rates well below 1% which means your facility can run without downtime between outages.
My Question as a Reliability Professional,
What is that Acceptable failure limit to your Enterprise?
Implementation & People
People is often overlooked in your preventative Maintenance Program and this is why your initiatives don't gain momentum and sustainability.
Successful Implementation of your electrical preventative maintenance program pivots on good engagement of people, far too many focus on technology and gadgets forgetting basic care.
The most important first step is gaining support from the customer (Usually the Owner or Executive) of your facility. Where do I focus, Where do we make the Profit, What is Critical. What is the current failure rate of the plant and can we improve on 0.8% failure rate.
When the Owner or Executive understands the opportunity comparing now to what is achievable, then you have won the first battle. The only issue they expect it to be implemented NOW!!!!
So present you strategy in manageable steps, and understand this is a journey not a magic wand.
Second step is to research the current practices, What is being checked and How? Ask does the task actually prevent an experienced failure. Too many programs a packed full of Gut feel failures and bloat your program swamping resources.
Do you have the Skills & Resources to make this a success?
Engagement: Armed with your data (Root Cause Analysis, Downtime, etc) engage your Electrical team in an open non controversial manner to discuss the how you can move forward. After the initial discussion a subject matter expert may be engaged to provide the "How & What".
Example: Our Vee Belts are only lasting one year, can you vendor provide some training, tools and procedures to increase service life?
Example: We experience a number of "burnt" High resistance small Crimp lugs on Motors. Again can our supplier train, provide procedures, and tools to get it solved.
This process requires engagement to uncover the common defects and solve the problems. Giving back a solution to your Team with correct training, procedures and often lacking tools.
Typical Problems: What are the problems in implementing Electrical Preventative Maintenance, it's a battlefield and nearly always time is precious. "The cry for resources is Endless".
How do you free up time to start, when you know the efforts will result in less reactive work which in turn frees up time?
Reactive Maintenance is a vicious cycle which if not managed falls quickly back to attending Breakdowns.
Solution: An Electrical Preventative Maintenance Program requires resourcing which you may think isn't available. A solution is to Examine exactly what your team is doing, are the current tasks adding to reliability?
e.g That Calibration done weekly never drifts much so can it be monthly?
If scoping of work done well then your Electrician isn't spending hours in the storeroom, and when the job starts is it suitable for Operations or does the your skilled trade go and have a cup of tea.
The reason you got your executive engaged first is sometimes ironing out these issues requires their support. e.g Sales want some extra, so the production running overtime but no one told Maintenance. Another hour or so is wasted.
Breaking the culture of waiting for a Breakdown needs to be eliminated. If you require assets to be nursed (Which is often planned) give that resource a preventative task that can be interrupted if needed. To often off shift resources aren't productively utilized.
You don't need much wriggle room to make a start, a couple of these issues solved may give you a couple of hours per week. That's enough to start.
The Who: If you have a champion, who is interested and keen to learn new skills and ways of doing work, your Electrical Preventative Maintenance will shine. If you spread the tasks too thinly you'll fail to get traction.
You will need to invest in some Skills even if it is a refresher, this will support this Champion. Engagement requires providing benefits to your team. It's an Investment!!!!!
Tools: To ensure the Electrical Preventative Maintenance Program doesn't stall, the workshop needs a tool review, matching what you want to achieve.
These might include a low range torque wrench 1 to 25Nm, Hydraulic Crimping Die tools, Milli Ohm meter, Motor Testing meter, and some decent hand tools like Torque Drivers.
Too often tools are provided by the Trades meaning only the basics are covered.
Procedures: Procedures are important for the smooth running of your Electrical Preventative Maintenance Program, and are they practical.
Is the Lock Out Tag Out process optimized, or is it taking longer than planned job.
The example above about torques, setting a standard for screw terminals say at 2.5 Nm means when one loosens you ask why? Eliminate the variability between people and you uncover the real problem.
Ask Will my Procedure Improve Reliability?
Visual: A visual check of your Electrical Assets is required annually in many countries by regulation, and the reason for this is most of the defects are detected by our eyes, feel, smell, and ears, but not Taste (I'm not keen on licking electrical stuff).
What to look for visually in your Electrical Preventative Maintenance Program varies tremendously between technicians, until a checklist is made and some skills transfer completed many potential defects are going to be missed. Checking the bottom nut on a motor termination for looseness is not often done, and is a common defect.
The reason why motor terminations aren't checked is because no one has pointed out the problem and shown the technician it is a common problem. Instead to many checklist have "Check the Motor" Tick Box which is completely useless.
This is why a checklist to standardize your tasks, and ensures each technician is conducting the same quality of work.
I have recently found a huge number of Crimp terminations misaligned causing High Resistance connections. This is an easy visual check and should be in a procedure.
There's a checklist within IEEE 1415:2006 that really only covers testing of Motors, www.3phi-reliability.com has further developed this checklist and its is available on request for clients.
A good quality checklist should identify known common failure modes and can include:
1. PE (Protective Earths) should not be corroded or placed on painted surfaces. Visually follow the entire length for any high resistive connections. An earth ground test with a Clamp meter can verify the resistance.
2. Visually check for any exposed live conductors, e.g. Cable damage from when conductors have been pulled through cabinet penetrations, excessive insulation tape is often a dead give away.
3. When first opening the cabinet take a smell of the enclosure. Capacitors often will vent, or visually dome on the ends when defective. Overheating of circuit breakers, poor terminations will have a plastic smell.
4. Separation of Supply and Drive Output Cables often show signs of blooming (White powder or burning near terminations). Insulation tape that has gone brittle is also an indicator of this degradation.
5. Dirt on the cooling fans exits of drives is an indicator that the Cabinet filters are missing. Dirt within drives is the most common failure mode as it causes tracking.
6. Drive fans need to be checked for airflow. Fan bearings have a finite life and should be checked regularly. It's best to find a bearing rattling than replace a blown drive.
7. Cabinets exposed to Vibration accelerates component failures especially in drives.
8. Cable strain either on Communication or Power terminations. Bend radius being tight can cause screen damage. Communication plugs not making a good connection because of cable strain or terminations where the conductor strands are broken (Normally hidden under tape).
Cleaning: Do not attempt to clean an electrical cabinet with Compressed Air, the results can be disastrous as debris can lodge into Contactors, Circuit Breakers and Isolators. In my previous role a maintenance supervisor did this and afterwards came to me to advise other sites not to do it.
Electrical Cabinets need to be clean, meaning filters regularly checked and changed. Ensure doors are closed and seal correctly for the filter to work. One of the most common failures in drives is dirt buildup which impedes heat dissipation and can cause tracking especially around the IGBT's (Switching Components).
Cleaning should be conducted with a filtered Vacuum cleaner.
Removal of Insulation Tape: My experience tells me that insulation tape is used to hide installation defects. If proper heat shrink sleeve is practiced then tape shouldn't be needed. If tape has become brittle be on the lookout for drive emission problems. High frequency currents degrade insulation and this tape is usually at the point where this current is trying to exit (Around Terminations).
What Should be included in your Electrical Preventative Maintenance Schedule?
You should be targeting common failure modes which may include:
Isolator connections & contact wear- Resistance Testing
High Resistive terminations at Motors
Motor Insulation Quality- measured with Insulation Resistance, Dissipation Factor, and/or Polarisation Index.
Motor Winding Degradation- measured with Phase Angle & Current Frequency Response.
Circuit Breaker Contact Degradation- measured with Micro Ohm Meter
Contactor Wear- Micro Ohm Meter
High Resistance Screw Terminals- Milli Ohm Resistance
Cable degradtion- SKF Tked1 for EMF Counts indicator of Drives reflective Voltages
Motor Rotor Defects- Dynamic Rotor Test
Bearing Currents- Attack on Motor Insulation, Cables, Terminations, Lubrication and Bearings. Measuring Transfer Impedance verifies proper grounding
Earth Loop Impedance & R1 + R2 resistances- Ensures safe grounding practices and is mandatory.
Resistance Testing: On Average 22% of Motor circuits have a resistive defect, and therefore this testing procedure is most rewarding.
When an imbalance in resistance of more than 3% is measured at the MCC, the test is then repeated at the motor terminals. This method quickly identifies where the defect exists.
Resistance imbalances affect the voltages each winding receives and this greatly stresses the winding resulting in shortened service life.
Motor Sizes 75kW or above have resistances below 10 milli Ohm therefore a micro Ohm meter is necessary to measure imbalances.
As a guide these motors may have balanced resistances above 10 milli Ohm but an opportunity exists to reduce resistance on all terminations.
Often termination practice has defects on all terminations.
Panel Screw Terminals: Why is connections in Electrical panels so important?
Many preventative maintenance programs check for tightness, but what is tight? The use of torque drivers set on an agreed setting enables monitoring. If a known tightness screw becomes loose then this should be flagged for investigation.
It is very common on the first scheduled work to find 50% plus connections loose.
While thermo graphs is useful defects will only show under load or starts, and many connections can be hidden from view.
Impedance Testing: Impedance determines how much current will flow in each winding, and in turn create a magnetic flux which drives the mechanical function of the motor.
This magnetic flux needs to be balanced for the motor to operate efficiently. An imbalance above 3% means your motor is likely not to meet energy efficiency requirements that are regulated in many countries.
If your motor circuit is balance <3% impedance imbalance and you measure a current imbalance when the motors runs this suggests you have an Inverter defect or supply problem. Note: When measuring variable speed drives currents, a meter is needed with a low pass filter and the ability to measure variable frequency. eg Fluke 381
Standard current clamps do not have this function.
Measuring Motor In Rush current on each phase under start conditions often amplifies a defect and makes it easier to detect.
Winding Testing: The most common winding test is a surge test unfortunately this instrument is quite bulky and expensive.
There is an alternative which uses a stepped frequency method which is validated under IEEE Standards. This portable battery operated instrument makes testing very efficient. The total test takes less than three minutes and at a fraction of the cost.
A winding test enable the condition of the Coil and Insulation to be assessed long before an Insulation Resistance meter picks up a change. Most winding defects develop while staying above 500 Mega Ohm phase to ground.
Insulation Resistance: This is a well known test for electrical workers and determines if a circuit is near failure.
A slightly earlier method is to measure phase to phase without the links connected.
3Phi Reliability recommend limits of circuits that are:
1. Trending below 100 Mega Ohm
2. Absolute limit of 40 Mega Ohm temperature corrected to IEEE 43-2000
Polarisation Index and Dissipation Factor can provide far more insight to the insulation health.
Thermal Image: What are the limitations of Thermography?
1. You must stand in front of a board while it's live, that has risks.
2. The heat emitted is a function of I^2R losses, so that means the load needs to be relatively high, that has risks. Often that condition is only met under start conditions.
3. Many of the connections in a circuit are hidden or have limited access.
e.g Isolators, Motor Terminations, Cable joins in conduit.
While Thermography is a good tool for detecting hot spots in in Motors, Mechanical defects and Process problems, resistance testing is far more effective in detecting the Electrical circuit defect. Also the risks are lower as testing is conducted in a de energized state.
Arguments around infra red windows can be installed but I've never seen one on a Motor or Isolator.
Asset Strategy: How often should Electrical Equipment be checked?
There are regulatory requirements for Industrial facilities which state testing must be on a three yearly schedule.
When first implementing an Electrical Preventative Maintenance Program you are likely to be in a reactive style of work, with majority of technicians attending breakdowns.
You haven't time to wait three years?
The recommended solution is to target larger critical Motors systems that are on drives or star delta starters. Data shows 37% of Motors are on Drives but account for 82% of winding defects.
Then Star Delta Starters where the high starting current exists, and then moving onto motors with a high number of starts, e.g Conveyors.
Alternatively during your next outage get the assistance of 3Phi Reliability to test your total site while's it's available.
The technology of Motor Circuit Analysis compliments Vibration Analysis, often a Spectra in Vibration Analysis will detect a 100 hz peak and further root cause analysis is needed. Motor Circuit Analysis pin points these electrical defects.
Reporting & Remedial Work: Why is it so essential to report your Electrical Preventative Maintenance measurements?
1. It is a regulatory requirement to show proof of the preventative Maintenance Program. Often it's the only defense if someone is injured.
2. When your program has matured and showing results your facility may wish to seek a re rating of the insurance risk.
This can have a significant reward for good work.
An audited program requires each test to be date and time stamped.
An Electrical Preventative Maintenance Program often reduces the ignition risk and that is the basis of the Insurance re rating.
3. Recording the measurement allows for monitoring, if you find a defect you want to be able to go into the history showing previous tests to see what has changed.
Analysis: Why will your Customer (Owner or Executive) be interested to know "What are the numbers" and the results of the Electrical Preventative Maintenance Program?
1. Is it worth spending the resources on this work?
2. Has there been a reduction in failure rates?
3. Where do we rank with failure rates, are we below 0.8%?
4. How can we improve?
Lastly a documented Electrical Preventative Maintenance Program that you have implemented is a great achievement and should be front and center on you CV.
Mark Gurney Motor Analyst/ Reliability Professional
Blog Free Advice on Electric Motor Reliability and Energy Savings
Feel free to Copy Link and use on your Website (Blue Chain Button)- MENU ABOVE