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Predictive Maintenance: extending the life of a motor

Predictive maintenance of Motor systems is a critical task to implement in any facility. It is designed to boost uptime, maximize productivity and increase revenue at the same time. Off-line or static tests are only necessary periodically based on your maintenance period. What’s more, the motor may still be operated while performing in-service or dynamic testing to determine potential or existing problems in your electric motors.

Companies using PdM programs prevent downtime & extend the lives of motorsClick To Tweet

Predictive Maintenance Benefits

Organizations that employ Predictive Maintenance programs in their facilities can prevent unplanned downtime, which can significantly impact production and normal business operations. Also, such program can extend the lives of rotating equipment and motors, which spares the company from spending so much on replacement of motors due to premature failure. Predictive maintenance analyzes the health trends of your electric motors as load and power quality are determined through periodic tests.

There are two types of test equipment used for electric motors – the dynamic and the static testing. The latter reproduces a real-world situation on motors that are off-line while the other type of test equipment monitors motors while in use.

Data gathered from a static motor test offer information on the condition and quality of the motor circuit and insulation. With the use of advanced technology in test equipment, potential failures that may arise in a motor are detected before these get worse. The discharge test is an important part of the testing method, as this determines the integrity and reliability of turn to turn insulation. During the testing period, reports and trend logs are gathered, which technicians analyze in checking for degradation or decline to the health of motors.

Organizations employing predictive maintenance programs are able to prevent unplanned downtimeClick To Tweet

Vibration Analysis

As for dynamic tests, equipment used help determine load problems of power-related concerns in motors. Other issues include circuit condition and vibration that are evident while operating the motor. Analyzers who perform these tests calculate the torque and speed, as well as determine rotor bar issues and check distortion levels. Mechanical issues such as motor shaft misalignment and bearing problems are also identified.

Mainly, predictive maintenance aims to reduce unnecessary downtime. The root of failure is determined before significant problems arise, which can spare you from costly repairs or replacement. Through dynamic and static test analysis, technicians are properly guided on how to maintain the condition of motors and prolong its lifespan.

Static Testing

Also called off-line testing, static testing is performed during power outages in a facility or periodically. To determine the quality of rewound, reconditioned or brand new motors, this type of test is also done. By doing so, the appropriate motor function is ensured before it is stored or used. Static tests also offer a baseline that will be helpful in measuring future tests.

Most static tests involve a series of procedures including winding resistance, meg-Ohm, polarization index, DC step voltage, followed by surge testing. This sequence is followed, and modern pieces of equipment are used in each process. Throughout the procedure, real-world situations are reproduced by analyzers while sparing the condition of the insulation system of the motor.

A test performed in checking winding resistance determines whether the motor’s phases are well-balanced. Thus, out-of-spec resistance connections opens, and shorts are monitored in the motor’s windings. As for the meg-Ohm test, this checks for contamination or grounding in the windings, and a meg-Ohm meter is used. When a low meg-Ohm result is obtained, it may mean an impending failure. As for a high meg-Ohm value, this does not completely indicate an absence of a problem in the motor.

Next, a polarization index test is performed to determined degraded insulation in a motor. However, it cannot be used to check for copper-to-copper faults since it only focuses on the condition of the motor’s insulation. The DC step voltage test, on the other hand, is used to identify cable problems and poor ground-wall insulation. It is done at double the line voltage with an additional 1000 volts without causing issues on the motor insulation once properly implemented.

The last phase of the testing period is the surge test, which can locate poor insulation, turn to turn. Any copper-to-copper faults are also detected, which are the main cause of about 80% of winding-related damages and failures. Once the weak insulation is located at its initial stage, repairs can be done before significant damages occur. So, loss of production, costly repairs, and unscheduled downtime are prevented.

Dynamic testing

In-service, or dynamic, testing refers to the test performed on motors while it is run. It is intended to gather data that reveal any distortion, unbalances and issues with the voltage level or power quality of the motor. A simple multimeter or Amp probe reading cannot determine minor harmonic voltage distortion, yet this can be obtained through dynamic tests. While this type of test is a relatively new approach, it is becoming a standard procedure for monitoring the condition of motors. It is also intended to be done more often that static testing.

Analyzers who perform dynamic testing are capable of predicting potential or existing failures on rotor bars with a steady load. The motor is stressed by the load under normal operation. During the test, a torque waveform is gathered, and this is analyzed to determine the stress level and check for mechanical concerns such as belt flapping and cavitation presented in the image.

Newer dynamic and static testers come in portable sizes, and these may be used on-site such as in the case of static testers. As for dynamic testers, these are used in the field or any place where the motors being used are located. Modern testers are now created such as the online motor analyzer, which is installed permanently, and it is in proximity to areas of 32 motors through motor buses within the motor control center. Thus, aside from being capable of performing similar tests done by a dynamic motor tester, this allows for continuous viewing and monitoring of the motor’s status from any place in the world (as long as there is a computer and internet connection). Information can be quickly captured, which may not be possible with one testing session using a portable dynamic tester. Trend data gathered from several months of monitoring can also provide the indispensable insight necessary for an effective predictive maintenance planning. Lastly, safety hazards during in-service tests on motors while in the field can be prevented through remote monitoring.

Through dynamic and static testing, your company’s predictive maintenance program can lead to successful results. A combination of these tests offers comprehensive data on the motor’s health, which will allow you to implement the right solution for obtaining an accurate diagnosis of the problem.


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Predictive Maintenance: extending the life of a motor


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