Detecting and Trending Winding Shorts Using Motor Circuit Analysis
Part 1
Howard W Penrose, Ph.D.
General Manager, ALL-TEST Pro
A Division of BJM Corp
hpenrose@bjmcorp.com
Introduction
One of the primary concerns in any electric motor diagnostics program is ‘how long can I operate the equipment?’ following fault detection. In the case of low voltage (less than 600 volts) equipment, the time may be measured in months, years or seconds. The key is discovering the amount of information that you have available and applying the knowledge.
In this first of a series of BLOGs, we shall review over twelve years worth of electric motor research in this subject and where the research has taken the author.
Motor Repair Research
The early research projects started with comparative reviews of motor repair practices and reliability up through 1994. The primary concerns were the electrical and mechanical impacts of winding removal, rewind, machining, insulation systems and test methods. The evaluation and research included:
1. Winding Removal and impact on the stator
1.1. Burn out ovens
1.2. Direct flame and other thermal methods
1.3. Dreisilker/Thumm method
1.4. Core materials
1.5. Mechanical variation
1.6. Core damage impact on winding life and efficiency
2. Rewind Methods and impact on energy and reliability
2.1. Hand winding
2.2. Automatic winding machines
2.3. Computer controlled winding machines
2.4. Winding modification
3. Insulation systems
3.1. Amount and type of insulation materials impact on reliability
3.2. Varnishing systems and impact
4. Machining impacts
4.1. Peening
4.2. Metalizing
4.3. Welding
4.4. Sleeving
5. Test methods
5.1. Test methods for verifying condition
5.2. Measurements and quality control
The studies included work performed by Ontario Hydro, Hydro Quebec, BC Hydro and Dreisilker Electric Motors, Inc. These research projects will be reviewed and discussed in detail in the coming days.
Motor Repair for Inverter Applications and Field Testing
Through 1997, a series of field studies were performed by Dreisilker Electric Motors, Inc’s Field Service and Research and Development Department led by Howard W Penrose who served as the Director of Field Service and Research and Development from 1992 to 1997.
The research involved research standards for motor repair related to motors in inverter environments, including the reliability of existing motors for these applications. The study included evaluating the method of winding failure within inverter environments and early detection of the problems that lead to these failures. A repair standard was developed based upon the results of the project.
Electric motor system maintenance and management programs were also developed in 1994 through 1996 with full application following that time. The program centered around the US Department of Energy’s MotorMaster Plus software and is still in application today.
Electric Motor Energy and Reliability
Through 1999, Dr Penrose continued his research as a Senior Research Engineer at the University of Illinois’ Energy Resources Center. Phase one was a project relating to the impact of burn out ovens on the stator frame, soft-foot conditions and air gap eccentricity. Phase two related to industrial evaluations for energy, reliability, production and waste stream studies. Phase three consisted of the PG&E Performance Analysis Tool which involved reviewing electric motor condition and estimating time to failure. The key to phase three was the application of Motor Circuit Analysis techniques.
Motor Circuit Analysis Techniques for Reliability and Time to Failure
Starting in 2000 and continuing today, research has been performed by ALL-TEST Pro, A Division of BJM Corp, in collaboration with equipment users, on data interpretation, motor diagnostic applications and time to failure studies. These will be the primary focus following updates and references to the previously published studies.
Each of the studies have been published through the Institute of Electrical and Electronics Engineers, Inc. (IEEE), a variety of other professional societies, industry publications and white papers. Most of these remain available via the web. The following presentations will link to these papers.
ABSTRACT for the following paper
Low Voltage Vs High Voltage Testing (follow this link)
by Dr. Howard W. Penrose, Ph.D.
Since the mid-1980’s, new technologies have been introduced that perform low voltage nondestructive evaluation of your electrical rotating machinery. Prior to this introduction, high voltage test method manufacturers would commonly caution users about the potential destructive tendencies of their technologies.
After this period, the story changed as the low voltage technologies took market share. The result? Marketing became the driving force with engineering the victim.
It is the purpose of this paper to discuss some of the myth and misdirection presented, and to reaffirm the direction of the industry. For de-energized Motor Circuit Analysis (MCA), the capabilities include: Cable faults; Winding shorts; Insulation to ground faults; and, Rotor/Air gap issues.
Understanding the Tests that are Recommended for Electric Motor Predictive Maintenance by Curtis Lanham, President, Baker Instrument Company
Abstract:
This paper will discuss the root causes of electrical failures in motors and how high voltage testing can help in early detection. The paper will review the insulation resistance test, polarization index test, DC hipot test, and the surge test along with outline the types of problems they can and cannot find.
Most electrical failures are caused by a combination of the voltage spikes that occur at start up and normal deterioration. The problem often begins as a turn-to-turn short that will eventually go to ground. Without high voltage testing many of these problems will go undetected.