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The Snell Group...Our Knowledge. Your Advantage

Motor Circuit Analysis eBrief

June 2008

Greetings Fellow Thermographers,

As a recipient of our Infrared eBriefs, you may already know that The Snell Group is producing a new e-newsletter dedicated to Motor Circuit Analysis. Similar to our regular Infrared eBriefs, this new e-newsletter contains updates on upcoming MCA training classes, useful tips on motor circuit testing, details on available MCA consulting and inspection services as well as information regarding online resources for motor technicians.

Please Note: This is the last sample issue that we'll be sending to our Infrared eBrief distribution list. In order to continue receiving our new MCA e-newsletter, those interested must register by subscribing via the following link:

Register for MCA eBriefs from The Snell Group

Thank you for your time during this special trial offer. We hope you enjoy the content.

Upcoming MCA Training

Motor Circuit Analysis - Offline

Charleston, South Carolina, September 15-19

Price: $1,895 USD/person

REGISTER HERE

Course Overview: The intent of The Snell Group's training course is to simplify the motor testing process by examining the individual tests utilized by today’s motor circuit analysis equipment. LEARN MORE

On-Site MCA Training

Motor Circuit Analysis courses can also be administered for one set price as a customized on-site training class at your location. There are many advantages to hosting an onsite including:

  • A lower total training cost for groups with six or more participants.
  • The ability to integrate hands-on field work with your plant’s equipment.
  • A lower student to teacher ratio, maximizing the attendees learning experience.

To receive a quote on a customized on-site training class, please contact us online via this link.

Motor Circuit Analysis Case Study

Overview

During a recent inspection a Snell Group technician conducting an offline motor test at the Motor Control Center Starter found a 45% resistive imbalance. This imbalance appeared to be on B-phase.

The motor in question needed to be returned to service the next day. As there was not sufficient time to isolate the high resistance problem the customer planned to monitor the system closely. Returning to conduct a follow-up scan with his infrared camera, the technician now found what appeared to be a current imbalance at the local disconnect for the motor in question. Thinking he would also find a "high resistance connection" because of what the previous day’s motor test indicated, the technician was instead surprised to see that B-phase was in fact running cooler than the other phases with no apparent connection problem.

Additionally, a clamp-on ammeter also indicated higher current in both A & C phases explaining why A & C-phases were running warmer.

What is happening with this circuit?

The problem was not at the local disconnect, but was instead on B-phase at the motor connection box. The issue was confirmed by a thermal image showing a hot B-phase wire at the termination, caused by high resistance at the connection.

Outcome:

A three phase motor with high resistance in one phase still tries to carry the entire load it is driving. As such it will draw more current through the other two phases until the over current protection circuits trip. This explains why the two phases, which were warmer and had higher current at the local disconnect, were not the phases which had the connection problem.

Lesson Learned:

Whenever possible confirm fault data with a second or third technology, in this case thermal imaging and an amp reading.

New MCA White Papers Posted to Knowledge Center

The Snell Group is pleased to announce that new White Papers have been posted to the online Knowledge Center and are now available for free download (with registration) through June 30th, 2008.

White Papers are professional technical articles written by instructors, consultants and inspectors who have, combined, hundreds of years of experience in the industry teaching and practicing both infrared and motor circuit analysis.

Thermal Profiles of Electric Motors and Their Relationship to Motor Circuit Analysis

By Elmer DeForest

Download Here

Read about a study that was performed on twenty-one motors. Eighteen of them were identical motors in identical service with the same model number and sequential serial numbers. This created a unique situation where motor data could be compared and analyzed.

Understanding Motor Starter Circuits

By Roy Huff

Download Here

Whether it’s your first infrared inspection or you’re a veteran with hundreds of surveys under your belt, understanding the equipment under inspection is crucial to the successful identification and analysis of thermal anomalies. This paper will identify and discuss the components and potential problem areas involved with motor starter circuits. It will also look at methods of infrared inspection and illustrate some common and some not-so-common thermal anomalies.

About The Snell Group

We are the world’s leading expert on using Infrared Thermography (IR) and Motor Circuit Analysis (MCA) to reduce risk, increase uptime, save money, conserve energy and improve safety. The Snell Group offers training, certification, inspection, consulting and information services for IR and MCA professionals and their programs world-wide.

Learn more at www.thesnellgroup.com