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Identifying Electric Motor Health through Motor Circuit Analysis

Identifying Electric Motor Health through Motor Circuit Analysis

HOW LONG HAVE I GOT is Often the question I get when a Motor tests bad.

Testing of Electric Motors entire circuit from the Motor Control Center is essential to eliminating Motor failures. It only takes two surveys to weed out the problems and stop more than 90% of Motor Failures.

During that work on going Energy Savings contribute to the time spent and nearly always exceed the costs in the first year.

The ALL TEST Pro instruments use test methods listed in IEEE 1415:2006 as an "Effective Means of Identifying Winding Condition".

These tests can effectively identify Turn to Turn, Coil to Coil, Phase to Phase, and Phase to Ground condition. The identification of the defect type allows an estimate to be made on on Remaining Time to Failure combined with Starting Frequency, Supply Quality, Environmental Factors and Loading.

The recommended Asset Strategy in Best Practice Motor Management is to identify your Motor condition through Health Assessments, together with a judgement of How critical the Motor is to your facility.

This first step provides you with the Risk to your business.

Using this Risk a suitable Asset Strategy then can be chosen and this may be:

1. Replacement with a critical Spare that is held onsite, before it fails

2. Plan the replacement before the Motor Fails, by purchasing from Vendor

3. Negotiate that your Motor Vendor Hold a spare for you, and take the risk of Response time and possible stock out

4. Don't have a strategy and HOPE you have a working spare when the Motor is RUN TO FAILURE. Rush the purchase and accept any motor what ever the condition.

5. Rush a Rewind or Overhaul, and suffer the Down Time.

Sadly most facilities default to the last two options, not knowing when the next Motor is going to drop.

This is What is called a Reactive Strategy where the Machine dictates what people do. The strategy is to reverse this situation and Ensure People are in Control of the Electric Motors.

This Control is Safer for Personnel, Reduces Downtime, Lowers the Total Cost of Ownership, and the Insurance Risk is lowered. (Lower premiums can be negotiated).

I praise facilities who REVERSE THIS SITUATION, and desire to be in Control, but often after the first survey I get the same question.


If a suitable Strategy has been developed then it probably doesn't matter because your in Control. The Question is the result of being in a REACTIVE STRATEGY where operations are scared of the failure.


To elevate this fear of failure ALL TEST PRO have developed a great little Estimator. While not guaranteed it is quite accurat

Remaining Motor Life Estimator

These estimates are based upon the research as published in IEEE Dielectric and Electrical Insulation Society (DEIS) conference papers.

So if your Proactive Strategy isn't quite developed or wish to know how much planning time you have to replace the Motor the estimator is very useful.  It answers the question will the Motor last until my next Maintenance Window (Shutdown).

This was that Motor Test:

MegOhm OK, Resistance OK, Winding Defect Identified

If you look at the Resistance, and Insulation Resistance Tests they Passed.

These two tests are traditionally used by Electricians to assess Motor Condition and this Motor would have Passed with no problems.

Traditional Motor Tests do not identify the very common Turn to Turn shorts, and Coil to Coil, but possibly a Phase to Phase or Phase to Ground could be detected.

Different levels of severity exist between these Winding defects, a Turn to turn short in the same winding coil on average takes longer to go to failure. A Coil to Coil, or Phase to Phase short has a much shorter time to failure, and a ground fault is near failure with no usable planning time.

There are analysis rules to identify these types of defects,

Generally (80% Predictability), and regardless of Motor Size:

A Turn to Turn short is when Phase Angle & Current Frequency response are > 2 from Average.

A Coil to Coil Short Phase Angle > 1 from Average, & Current Frequency is <2

A Phase to Phase Short is determined by Phase Angle <1, and Current Frequency Response > 2 from Average.

It is essential your technical staff have the tools to complete a full motor test identifying all the possible defects, including Isolators, cables, and Terminations.

The two winding tests can be viewed in my blog posts:

Phase Angle

Current Frequency Response

Other tests such as Inductance, Impedance, Dissipation Factor, Capacitance, Insulation Resistance, 4 Wire Resistance Testing, are included in the Motor Testing to complete a comprehensive Analysis.

Motor Management

When you engage 3Phi Reliability your personnel receive Termination guidelines, method of fault finding to quickly identify defects and these are the areas of ENERGY SAVINGS.  The estimator is part of that guidance.

It is highly recommended that you Motor Test all your existing Critical Spares, and implement the same testing on Newly purchased and Overhauled Motors. This ensures that your spares are FIT FOR USE.

Once you pay for a Motor New or Overhauled Motor its YOURS, make sure its a good one.  It is surprising how many should be returned.

3Phi Reliability is an independent unbiased service which has no commercial ties to Motor Manufacturers. Speak to us and the real quality issues in Electric Motors.

When your Best Practice Motor Management strategy is implemented it allows planning time and motor defects aren't forced upon you to accept them due to time constraints.

Yon can then setup a Motor Store which is Kind to your Motors

If you desire to reverse the REACTIVE strategy, and GAIN ELECTRIC MOTOR RELIABILITY & RETURN ENERGY SAVINGS then a prompt reply will be provided to your inquiry.

3Phi Reliability wish you all the best in your goal of Lower Cost of Ownership.

Best Practice Motor Management

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3Phi Reliability strive to provide interesting and informative topics to clients to Gain Electric Motor Reliability and Return Energy Savings

Gain Electric Motor Reliability & Return Energy Savings

Most of clients make gains on the every first day of implementation. Best Practice Motor Management has a short Return on Investment, improving Electric Motor Reliability and Energy Savings are immediate.