Electric motors consume over 25% of the world’s electric power. In industrial facilities motors account for most of the power consumption. Despite the vast amounts of energy they consume, motors are some of the most efficient pieces of machinery ever created. Motors that are properly maintained and loaded to their design limits, provide efficiencies that are upwards of 95%. In more simple terms we get 95% work out of the 100% energy consumed. Compare that to our average motor vehicle where a 20% efficiency would be considered remarkable. All of that being stated, for the most part, motors are neglected and do not come close to the longevity that they can easily attain. Motors are like a roof on a building or tires on a vehicle. We don’t think much about a roof until it leaks, we don’t think about tires until they go flat, we don’t think about motors until they fail. Yet motors are some of the easiest equipment to maintain. The U.S. Department of Energy, DOE, conducted a study and determined that proper motor maintenance can increase motor efficiencies by 16%.
In 1986, the Electric Power Research Institute (EPRI) funded General Electric to conduct a study on the causes of motor failures.
The test group of medium and high voltage motors showed that at minimum 37% stator and 10% rotor failures, or 47% electrical failures with 41% bearing failures. No further study was accomplished to determine if or how many bearing failures were electrically induced. The overall results of the study revealed that monitoring motors with specific testing equipment could mitigate a considerable number of catastrophic electrical motor failures.
Companies started up with specific goals of providing motor test instruments. Until the EPRI study, motor test equipage was minimal, a multimeter and maybe a meg-ohmmeter. Computers also helped accelerate motor testing and technology development. Use of computers to control inductance and capacitance bridges, digital low resistance ohmmeter development, coupling the power and versatility of computer software and acquired motor test data, in a brief time, revolutionized the monitoring of electric motors.
De-energized motor testing has been predominantly performed in the motor repair industry. Use of surge and hi-pot equipage was common in reputable repair facilities as a means of identifying motor faults as well as a quality assurance method for checking the integrity of rewinds. These equipments eventually became modified to provide a reliability maintenance-based platform and can be found in commercial and industrial facilities all over the world.
The newest reliability tool in the predictive maintenance tool box is “energized” electric motor testing. This emerging technology has tremendous capabilities coupled with expedient data collection. In addition to providing a good insight into a facilities power quality, the technology also provides a means of identifying numerous electrical and mechanical anomalies.
It was discovered in the in the 1960’s that electrical load anomalies would modulate current. The process involved in determining the “affect frequencies” required extensive signal processing calculations. The process required computers and was not cost-effective in that time period. The Department of Energy and Robert Gordon Institute of Technology, in Aberdeen, Scotland, worked to develop a cost effect and simple method to conduct the necessary signal processing.
This process is more commonly known as a Fast Fourier Transform (FFT). Energized motor testing instruments have been around in rudimentary form since the early 1980’s. This was a result of a need expressed in the early 1970’s for a method of testing remotely operated valves in the containment areas of nuclear power plants. The Department of Energy answered, and the Oak Ridge National Laboratory (ORNL) oversaw development of motor current signature analysis, MCSA. The advent of the personal computer and vibration data loggers provided the platforms necessary for this data collection and complex analysis. The vibration data logger provided a single channel control transformer input. Vendor software provided for segregating the component frequencies and magnitudes riding on the fundamental 60HZ waveform.
Compared with today’s motor test instruments that collect 6 channel data, a single-phase capture seems insignificant. However, when monitoring current in an FFT spectral presentation, we still, in most cases, just monitor one phase. What has evolved from the research in the 1960’s and the needs expressed in the 1970’s are energized motor test instruments that provide analysis capability for many power quality issues as well as electrical and mechanical anomalies.
Energized motor testing has both benefits and concerns. The benefits are that it provides a means of identifying electrical and mechanical problems that contribute to a reduction in motor longevity. It enables expedient testing without necessitating equipment shut down. The concerns are we must test energized and that requires working in the vicinity of energized electrical equipment. Of considerable importance; when testing energized, we cannot evaluate the circuit insulation integrity. “Partial discharge” test instruments are capable of some testing of insulation on energized equipment, but currently motor tester vendors do not combine the partial discharge capability with power quality and signature analysis equipment.
With all the test equipment, methods and practices now available specifically for testing electric motors, the new problem is a huge knowledge void. Understanding motor operation, failure mechanisms and the diagnostics available to detect problems before they result in catastrophic failure is an area where little training is available. Vendors of motor test instruments teach their specific equipment’s operation and software, but few places provide comprehensive training including technical schools, colleges and universities.
The Snell Group realized this need and developed comprehensive “hands-on” curriculums for both energized and de-energized electric motor testing as well as a combined course that includes both curriculums in a condensed 1-week course.