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. See my blog
Failure rates from 1983 Electric Power Research Institute (EPRI) project performed by General Electric (GE) [1] where 4797 motors were evaluated with 1227 failures. State failure rates of Motors 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, Drives, Isolators, Cables and Terminations etc).
Even at the Average a facility with 500 motors that’s an electrical failure every 21 days which if critical will take your plant down.
An Electrical Preventative Maintenance Program is considered excellent if the failures rates are less than 1%, that’s one failure every 2 Months.
Best Practice Motor Management can achieve failure rates well below 1% which means your facility can run without downtime between outages.
My question is As a Reliability Professional,
What Is that Acceptable failure limit to Your Enterprise?
Implementation & People
This is often overlooked in your Preventative Maintenance Program and why your initiatives don’t gain momentum and sustainability. Successful Implementation of your Electrical Preventative Program pivots on good engagement of people.
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 improved on 0.8% failure rate?
Second is to research the current practices, What is being checked and How.
Do you have the Skills & Resources to make a success?
Engagement: Armed with you data (Root Cause Analysis, downtime etc) engage you electrical team in a 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 to” & “What”.
Typical Problems: What are the problems in Implementing Electrical Preventative Maintenance, its 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 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. erg. That Calibration done weekly never drifts much so can it be monthly. If Scoping of work is done well so your Electrician isn’t spending hours in the storeroom, and When the job starts is it suitable for the Operations or does your skilled trade go and have another cup of tea.
The reason you got your your executive engaged first is sometimes ironing these issues out requires their support.
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 your Champion.
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 Tool, MilliOhm meter, Motor testing meter, and some decent hand tools like torque drivers.
Procedures: Procedures are important to for the smooth working of your Electrical Preventative Maintenance Programme, Is the Lock Out Tag Out process optimized and taking longer than the planned job, is my Champion a competent electrical worker, what tests are you going to conduct and What are the expected defects to be identified.
Will my procedure improve reliability?
Electrical Preventative Checklist
Visual: A visual check of you Electrical Assets is required annually, and the reason for this is most of the defects are detected by our eyes,feel,smell,ears, but not Taste (I’m not keen on licking electrical stuff).
What to look for visually in you 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 has pointed out the problem and shown the technician it is a common problem.
This is why a checklist is important to standardized your Electrical preventative maintenance program, it ensures each technician is conducting the same quality of work.
There’s a checklist within IEEE 1415:2006 that really only covers motors, 3Phi Reliability has further developed this checklist and it is available on request for clients.
A good quality checklist should identify known common failure modes and can include:
1. PE (Protective Earths) should be not corroded or placed on painted surfaces. Visually follow the entire length for any high resistance defects.
2. Visually check for any exposed live conductors, eg 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 the ends will dome when defective. Overheating of circuit breakers, poor terminations will have a plastic smell.
4. Separation of Supply and Drive Output cables often shown signs of blooming (White Powder or burning near terminations). Insulation tape that has gone brittle is also a indicator of 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. Drives fans need to be checked for airflow. Fan bearings have a finite life and should be checked regularly.
7. Cabinets exposed to vibration accelerates component failures especially in drives.
8. Cable strain either on Communications or Power terminations. Communication plugs not making a good connection because of cable strain or terminations were 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).
Removal of Insulation Tape: My experience tells me that Insulation tape is used to hide installation defects. 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).
Testing of Electrical Equipment: What should be included in your Electrical Preventative Maintenance Schedule?
You should be targeting common failure modes which include:
Isolators connections contacts and wear
High Resistive Terminations at Motors
Motor Insulation Quality
Motor Winding degradation
Circuit Breaker Contact degradation
Contactor Wear
High Resistance Screw Terminals
Cable degradation
Motor Rotor defects
Drive Emission attack on Motors, Cables,and Terminations
Earth Loop Impedance & R1 + R2 ensuring safe grounding
Resistance Testing: On average 22% of Motor circuits have a resistive defect, and therefore this testing procedure is the most rewarding.
The use of a Micro Ohm or MilliOhm meter from the Electrical Cabinet will identify imbalances in the entire circuit.
When an imbalance of more than 3% is measured, 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.
Motor sizes 75kW or above have resistances below 10 milliOhm therefore a micro Ohm meter is necessary to measure imbalances.
As a guide these motors may have balanced resistances above 10 milliOhm but an opportunity exists to check all terminations.
Often the termination practice has defects on all connections.
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 this should be noted on the Work Order for followup.
It is very common on the first scheduled work to find 50% plus connections loose.
Impedance Testing: Impedance determines how much current will flow in each winding, and in turn create magnetic flux which drives the mechanical function of the motor.
This magnetic flux needs to be balanced for the motor to operate efficiently. A 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 balanced <3% impedance imbalance and you measure a current imbalance when the motor runs this suggests you have a drive defect or supply problem. Note: When measuring variable speed drive current, a meter is needed with a low pass filter and ability to measure at the operating frequency.
Standard current clamps do not have this function.
Measuring Motor In Rush current on each phase under starting conditions often amplifies a defect and makes it easier to detect.
Winding Testing: The most common winding test is surge testing, unfortunately the instrument is quite bulky and expensive.
There is an alternative which uses a stepped frequency method validated under IEEE standards. This portable battery operated instrument makes testing very efficient. The total test takes less than 3 minutes and are fraction of the cost.
A winding test enables the condition of the coil and insulation to be assessed long before an Insulation Resistance picks up a change. Most winding defects develop while staying above 500 megaOhm phase to ground.
This winding test is the electrical equivalent of Vibration Analysis and compliment each other in a predictive maintenance program.
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 link connected. See here.
3Phi Reliability recommend limits of circuits that are:
1. Trending below 100 MegaOhm
2. Absolute limit of 40 MegaOhm.
Thermal Image: What are the limitations of Thermography?
1. You must stand in front of a board while its 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.
3. Many of the connections in a circuit are hidden or have limited access.
Eg Isolators, Motor Terminations, Cable joins in conduit.
While Thermography is a good tool for detecting hot spots in Motors, Mechanical defects, and Process problems Resistance Testing is far more effective in detecting the Electrical Circuit defects.
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?
The regulatory requirement for Industrial facilities is a three year 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 Motor systems that are on drives. Data shows 37% of Motors are on Drives but account for 82% of winding defects.
Then Star Delta Starters where high starting exist, and then motors with a high number of starts.
Alternatively during your next outage get the assistance of 3Phi Reliability to test your total site while it's available for testing
The technology of Motor Circuit Analysis compliments Vibration Analysis, often a Spectra in Vibration Analysis will detect 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.
2. When your program has matured and showing results your facility may wish to seek re rating of the Insurance Risk.
This can have significant financial 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 Insurance re rating.
3. Recording the measurements allows for monitoring, if you find a defect you want to be able to go into the history showing previous tests of that same circuit and see if a change has occurred.
Analysis: Why will Your customer (Owner or Executive) be very interested to know “What are the numbers” and 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% per annum.
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 your CV.
