Prevent Motor Failures with Partial Discharge Testing | Schleich

Motor Life: Not a Simple Concept

Mon, 28 Apr 2025 22:03:01 GMT

How long will a motor last?

It depends on what the meaning of the word "last" is: by Richard L. Nailen EA Engineering Editor

Adapted and summarized from “Motor Life: Not a Simple Concept,” Electrical Apparatus Magazine, December 2019.

Fast Facts: Quick Takeaways

Average Motor Failure Rate: ~10% per year (combining mechanical and electrical causes)
Top Failure Cause: Bearings (over 50% of failures)
Motor Life by HP: Motors above 50 HP last significantly longer
Rewinding Does Not End Life: Proper rewinding maintains efficiency
Biggest Life Factors: Environment, maintenance, load management
Efficiency vs Reliability: No significant reliability difference between standard and premium-efficiency motors

Introduction

How long will a motor last? It depends on what "lasting" means. Motor life is a complex topic shaped by numerous factors beyond simple operating hours.

A 1959 IEEE report published failure rates for a variety of electrical apparatus, including induction motors up to 200 horsepower. It showed an average annual failure rate around 10%, divided between electrical causes (3–4%) and mechanical causes (about 7%). Despite extensive studies over decades, predicting the life span of any individual motor remains elusive.

Understanding Motor Failure

Motor failure does not necessarily signal the end of a motor’s useful life. Motors often experience breakdowns that are repairable, meaning they can continue operating long after initial failure events.

Key Causes of Motor Failure:

Bearings (largest cause)
Winding failures
Environmental stresses (voltage, moisture, contaminants)
External mechanical damage
Unknown or multiple factors

A failure may merely trigger a repair— not total retirement of the motor. In fact, bearing replacement is cited as the most common reason motors enter the repair shop and is far less costly and time-consuming than rewinding.

Failure vs. End of Life

"Motor life" and "first failure" are not interchangeable concepts. Many motors can be repaired multiple times before actual retirement.

The true "end of life" is better defined by economics :

When the cost of repair outweighs the value of continued operation.
When replacement offers better long-term reliability and cost efficiency.

Proper repairs (especially rewinding) do not automatically shorten a motor's life or compromise efficiency when conducted to best-practice standards.

Factors Influencing Motor Life

Motor longevity is heavily influenced by a combination of factors:

Operating Environment: Exposure to dust, heat, moisture, vibration, and chemical agents.
Maintenance Quality: Timely bearing lubrication, alignment, insulation monitoring, and cooling management.
Motor Design and Materials: Original manufacturing quality and materials durability.
Installation Practices: Correct sizing, alignment, and connection methods.
Duty Cycle and Loading: Continuous overloads, frequent starts/stops, and harsh service conditions shorten life.

Motor Life Trends by Horsepower

Surveys and studies, including U.S. Department of Energy and IEEE data, suggest that motor life expectancy correlates with motor size:

Please see below table

Observation: Larger motors tend to have a longer average service life, partly due to sturdier designs and more careful maintenance practices.

Impact of Rewinding and Repairs

A common misconception is that a motor’s life ends with its first rewind.

In reality:

Properly rewound motors can maintain efficiency and reliability .
Industry studies (e.g., EASA/ANSI standards) show minimal efficiency loss when rewinding is performed correctly.

Graphs such as Figure 4 in the original publication demonstrate that performance deterioration is more dependent on poor repair practices than on the act of rewinding itself.

Motor Efficiency vs. Reliability

With the rise of energy-efficient motor designs, concerns emerged about whether “new” motors sacrifice longevity for higher efficiency.

Studies consistently show that, when comparing motors built to similar quality standards and operated under proper conditions:

There is no significant reliability gap between traditional and premium-efficiency motors.
Failures are more often due to operational and maintenance conditions, not motor design compromises.

Defining True "End of Life"

End of life for motors should be evaluated based on:

Percentage of motors reaching true worn-out condition.
Operating environment uniformity across surveyed populations.
Installation consistency.

"Motor life" should not be defined solely by "time to first failure," but by comprehensive serviceability and cost-effectiveness.

Common Misunderstandings About Motor Life

Motor failure does not equal motor end of life .
Time to first failure is not an accurate measure of motor lifespan.
Manufacturer life claims (like 20+ years) often lack rigorous experimental backing and depend heavily on environment and maintenance.

Key Practical Insights:

Motors operated part-time or lightly loaded often last far longer than continuous full-load motors.
Maintenance discipline remains the most reliable method to extend motor life .
Knowing "how long" is less important than knowing how to maintain and when replacement makes more sense than repair .

Conclusion

Motor life is not a simple, fixed figure.

It depends on:

The operating conditions
Maintenance practices
Economic evaluations

Rather than relying solely on theoretical life ratings, organizations should focus on proactive maintenance, careful repairs, and informed replacement strategies to optimize motor service life.

Motor longevity is, ultimately, a combination of engineering, economics, and maintenance discipline .

Appendix: Key Figures & Graphs

1. Causes of Motor Failure:

Bearings – 51%
Winding – 16%
External environment (voltage, moisture, etc.) – 16%
Unknown – 10%
Rotor – 5%
Shaft/Coupling – 2%

2. Motor Life by Horsepower Table: (See Motor Life Trends by Horsepower section above)

3. Efficiency After Rewinds:

Proper rewinding maintains original motor efficiency if best practices are followed.

4. Failure vs Repair Decision Chart:

Failure ➞ Assess ➞ Repair or Replace based on severity, application, and economic analysis.

Adapted and summarized from “Motor Life: Not a Simple Concept,” Electrical Apparatus, December 2019.

Original Photocopied article complete in PDF format can be found here at this link.

Modified article in clean format abridged can be found at this link.

Winding Test Techniques for Reliable Motor Diagnostics

john.wilson@mdsusa.net (John Wilson) — Wed, 19 Feb 2025 21:07:28 GMT

Advanced Winding Test Techniques for Enhanced Motor Reliability and Safety

Summary for the Test Method Handbook: Safety and Function Testers PDF:

Essential Safety & Function Testing for Electrical Compliance and Performance

Explore the definitive guide to winding insulation testing with Schleich's Test Method Handbook. This technical paper is an essential resource for engineers, maintenance teams, and quality control professionals involved in electric motor testing. It offers an in-depth breakdown of modern winding test strategies, including surge voltage testing, partial discharge, insulation resistance, high-potential (HiPot) testing, and more. Whether you're troubleshooting failures, validating motor quality, or designing new testing processes, this handbook delivers the practical insights and structured methodologies to ensure comprehensive motor analysis and long-term reliability.

�� Download the full handbook to deepen your expertise in Safety & Function Testing.

Comprehensive Guide to Motor Winding Testing & Diagnostics

john.wilson@mdsusa.net (John Wilson) — Wed, 19 Feb 2025 20:31:18 GMT

Ensuring Precision in Motor Winding Testing: A Comprehensive Guide

Summary for the Test Method Handbook: Winding Testers PDF:

Ensuring Precision in Motor Winding Testing: A Comprehensive Guide

In the world of motor diagnostics, ensuring the reliability and efficiency of winding systems is crucial. The Test Method Handbook: Winding Testers by Schleich provides an in-depth exploration of advanced testing techniques used to detect faults in electric motor windings. This essential resource covers key testing methodologies, including surge voltage tests, partial discharge detection, high-potential (HiPot) testing, and insulation resistance measurements. Whether you're in manufacturing, quality control, or maintenance, this guide offers invaluable insights to optimize motor performance and longevity.

�� Download the full handbook to deepen your expertise in winding diagnostics.

Prevent Motor Failures Before They Happen: The Power of Partial Discharge Testing

john.wilson@mdsusa.net (John Wilson) — Wed, 19 Feb 2025 18:39:33 GMT

A Critical Guide to Detecting Early Insulation Breakdowns and Ensuring Long-Term Motor Reliability

Innovative Test & Measurement Technology for Motors and Generators

The document discusses the importance and methodology of partial discharge testing in electric motors, particularly in the context of variable frequency drives (VFDs) and high-voltage applications, to assess insulation integrity and prevent catastrophic failures.

Summary for Partial Discharge Testing Paper Download

Enhancing Motor Reliability with Partial Discharge Testing

(Authors: Dipl.-Ing. Jan-Philipp Lahrmann, Dipl.-Ing. Martin Lahrmann)

As the use of Variable Frequency Drives (VFDs) continues to grow, ensuring the reliability of low-voltage electric motor insulation has never been more critical. Partial Discharge (PD) testing is a vital method for detecting early insulation failures that could lead to costly motor breakdowns and operational disruptions .

This comprehensive paper provides a detailed explanation of PD testing, including:

✅ What is Partial Discharge? – Learn how insulation defects lead to breakdowns.

✅ Causes & Consequences – Understand how undetected PD can erode insulation over time, leading to catastrophic motor failure.

✅ Testing Techniques – Compare high-voltage tests, surge tests, and PD inception/extinction voltage analysis.

✅ Applications & Best Practices – Discover why PD testing is crucial for motors operating under VFDs, high-voltage conditions, and industrial environments.

With insights from Schleich’s industry-leading test technology, this paper is an essential resource for maintenance teams, motor repair professionals, and manufacturers looking to improve motor longevity and performance.

�� Download the Whitepaper Now and take a proactive step in motor insulation health monitoring!

PD testing is essential for both manufacturing and maintenance of electric motors. SCHLEICH offers reliable PD testing equipment, combining high-voltage and surge tests, ensuring comprehensive motor diagnostics.

For more information, visit Our website or contact our sales team.

Contact: MOTOR DIAGNOSTIC SYSTEMS, INC. 6387 Aviation Circle, Loveland, Colorado, 80538

Email: inside.sales@mdsusa.net Phone: +1 (970) 461-1348 or +1 (877) 461-1348 Fax: +1 (866) 223-0800

Prevent Motor Failures with Partial Discharge Testing | Schleich

Motor Life: Not a Simple Concept

How long will a motor last?

It depends on what the meaning of the word "last" is: by Richard L. Nailen EA Engineering Editor

Adapted and summarized from “Motor Life: Not a Simple Concept,” Electrical Apparatus Magazine, December 2019.

Fast Facts: Quick Takeaways

Introduction

Understanding Motor Failure

Failure vs. End of Life

Factors Influencing Motor Life

Motor Life Trends by Horsepower

Impact of Rewinding and Repairs

Motor Efficiency vs. Reliability

Defining True "End of Life"

Common Misunderstandings About Motor Life

Conclusion

Appendix: Key Figures & Graphs

Winding Test Techniques for Reliable Motor Diagnostics

Advanced Winding Test Techniques for Enhanced Motor Reliability and Safety

Summary for the Test Method Handbook: Safety and Function Testers PDF:

Essential Safety & Function Testing for Electrical Compliance and Performance

Comprehensive Guide to Motor Winding Testing & Diagnostics

Ensuring Precision in Motor Winding Testing: A Comprehensive Guide

Summary for the Test Method Handbook: Winding Testers PDF:

Ensuring Precision in Motor Winding Testing: A Comprehensive Guide

Prevent Motor Failures Before They Happen: The Power of Partial Discharge Testing

A Critical Guide to Detecting Early Insulation Breakdowns and Ensuring Long-Term Motor Reliability

Innovative Test & Measurement Technology for Motors and Generators ​

Summary for Partial Discharge Testing Paper Download

Enhancing Motor Reliability with Partial Discharge Testing

Innovative Test & Measurement Technology for Motors and Generators