Motorblog

Energy and Reliability Analysis Using Motor Diagnostic Technologies

Electric motor energy retrofits offer facilities both energy and reliability opportunities. Unfortunately, in many cases, most companies will not consider the opportunities unless a two-year simple payback is identified.

The costs which are considered, that make the decisions challenging, include the full cost of the replacement motor, the labor involved in removing and re-installing and other associated costs. When reviewing the cost benefits of a few percent efficiency, the load and the actual annual operating hours, the payback may show as a great many years.

Instead, when considering a repair versus replace decision, the costs involved are only the difference between the replacement cost of the new motor and the repair costs of the old motor. In this case, the increase in efficiency will normally provide a generous return on investment. However, if left until it is time to make the repair versus replace decision, getting equipment up and running takes precedence over energy improvements.

Energy and premium efficient motors provide not just an improvement to energy costs, but are normally more reliable than standard efficient motors. Therefore, it is a benefit to both energy and reliability, and to the resulting bottom line, to use energy and premium efficient motors where possible.

Through all of this, another opportunity presents itself: Determine what motors are operating in poor condition and replace them before it becomes urgent. In 1989 through 1991, such a program was developed to consider electric motor and condition analysis. In the Performance Analysis Tool project, by Pacific Gas and Electric, electric motors were evaluated using datalogging instruments, motor circuit analysis, vibration analysis and the US Department of Energy’s MotorMaster Plus software.

Datalogging times varied depending upon the operation of the equipment. Vibration analysis, which required access to each electric motors, took longer. Motor circuit analysis time was quick, as testing was performed from the motor control center or disconnect. For example, testing 20 motors required less than 90 minutes to test with motor circuit analysis, another 90 minutes for basic electrical measurements and a full day using vibration analysis. It should be noted, however, that numerous maintenance opportunities were noted during the walk-through necessary to perform vibration.

In 1990, as part of the project, ALL-TEST Pro, A Division of BJM Corp, Dreisilker Electric Motors, Inc. and Pruftechnik co-funded modifications to MotorMaster Plus as the first US DOE Bestpractices (http://www.oit.doe.gov/bestpractices) Market Transfer success. Coordinated by Dr. Howard Penrose of ALL-TEST Pro, the modification included the ability to enter MCA, insulation to ground and vibration data directly into MotorMaster Plus, then to be able to sort the motors by condition.

The program was found to be very successful with the following comments:

1) While MCA was very successful, detecting 64% of the problems found within 1 of 6 motors tested, it required equipment to be de-energized.
2) Vibration analysis took a significant amount of time
3) Potential return was significant enough to make any inconveniences insignificant

Now, with the application and ability of motor current signature analysis to detect electrical and mechanical faults, a combination of motor circuit analysis and motor current signature analysis will allow a technician or analyst to take data and analyze it quickly. Coupled with MotorMaster Plus, an electric motor energy and condition analysis can be performed quickly and with great success.

There are several basic steps to such a program:

1) Select candidate motors to be evaluated
2) Collect motor nameplate information and note anything unusual
3) Collect MCSA data
4) Collect MCA data
5) Enter the findings into MotorMaster Plus
6) Run repair versus replace reports and return on investment reports
7) Make changes and enter data into MotorMaster Plus
8) Verify energy savings using MotorMaster Plus reporting features.

Selecting the electric motors for review will be the most challenging part of the project. The most successful programs select motors from 5 to 250 horsepower from one department, as a pilot project. Otherwise, full surveys of a large plant usually become overwhelming and are either not pursued or only partially successful. In addition, complete motor nameplate information is required for an accurate MotorMaster Plus survey. Ensure annual operating hours are noted.

A motor current signature analysis instrument which provide automated information on condition as well as reporting voltage, current, power factor, RPM and kW is recommended. If necessary, for variable loads, an MCSA device which allows datalogging should be selected. Motor circuit analysis data should be collected when the motor can be de-energized and a device selected which provides automated analysis.

Enter the nameplate information and findings into the MotorMaster Plus software. MCA information can be entered into the MotorMaster Plus maintenance fields and MCSA information can be entered into the vibration fields.

Repair versus replace reports can be run through MotorMaster Plus including condition analysis. Once the repair versus replace scenario has been run and printed, a cost analysis can then be performed.

For example: A 50 horsepower, 1775 RPM, 64.5 Amp, 440 Vac motor was tested on a Glycol pump in a critical application. It was determined that there were motor and driven equipment related mechanical problems including: Soft foot, stator faults, unbalance or misalignment, and looseness. A MotorMaster Plus study identified that the motor was operating at 75% of load and was 90.6% efficient. A premium efficient motor rated 94.9% efficient motor could be selected with a simple return on investment of 0.9 years. This equated to an after tax ROI of 366% and a benefit to cost ratio of 5.55. Simple decision to make.