Art of Electric Motor Repair Part 1

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This series is a re-run of a series that I had published in 2005 and includes some updates based upon changes in the industry. The series will also be kept on the MotorDoc blog at http://motordoc.com.

“There is no such thing as something for nothing.” Napoleon Hill

“81% of electric motor repair shops modify your windings through the rewind process. 73% of the modifications are for ease of rewind and shop preference. Less than 4% of modifications are for reliability.” 2003 Motor Diagnostics and Motor Health Study (http://motordoc.com archives)

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Introduction:

I started my career in the electric motor repair business, first as a US Navy electric motor repair journeyman (NEC 4621) then with Dreisilker Electric Motors, Inc. (Glen Ellyn, Illinois), and Dunkums Electric (Richmond, VA). The experience included performance, standards work, research and development, root cause failure analysis (forensics), warranty investigations and much more. I have literally performed the types of repair that I have recommended and have either performed or investigated repair that I warn about. Since 1997, when I was the senior research engineer at the University of Illinois’ Energy Resources Center, I started evaluating repair shops for end users. At the same time, since 1994, I have been directly involved in the development of standards for electric motor testing, manufacturing and repair.

As we progress in this lecture series, I am not only going to provide information concerning repair standards, specifications and practices, but information on the parts that directly impact reliability and motor life that are not covered by standards. This is important to understand, in your motor diagnostics and/or motor management program, because how your vendor takes care of your electric machine will directly impact your bottom line as well as your impact on the environment. We will cover electrical and mechanical repair processes.

What is Electric Motor Repair?

Within this part of the lecture series, we are going to define electric motor repair as the function of returning an electric motor to the ‘as new’ condition, regardless of its condition prior to the repair.

The scope of presentation will start with the beginning, removal, transportation to a repair facility, the repair process, the communication process between a repair facility and motor owner, testing and repair standards, transportation to the motor owner, commissioning and installation, root cause analysis by the owner and repair facility and developing a motor repair specification that the motor owner and repair facility can live with. Also included will be the repair versus replace decision, impact of repair on reliability, energy and environment. As such, we will explore each part of the repair process and options for each, which will be graded upon my personal experience and observations.

To be Continued….

Tech Tip: ALL-TEST PRO OL for Power Analysis

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One of the uses I have for the ALL-TEST PRO OL (ATPOL) electrical signature analyzer is power quality and power analysis studies. The settings in the ATPOL data collector can be changed via the memory card or Bluetooth with all of the associated settings including CT and PT ratios if data is being collected via CT or PT.

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Figure: Power Analysis Settings

These studies include harmonics, power factor, data logging, sags, swells, spikes and other conditions, and it is fully capable of taking this data in an inverter and DC machine environment.

In a recent case, we were reviewing inrush on a system. We set the datalogger to grab data every 0.1 second and allowed it to datalog through the starting cycle. This allowed us to watch the impact of the inrush and which system(s) tripped off line and at what times as larger electric machines started up. This allowed us to look at solutions for each of the systems.