Designed with sustainability in mind, electric motors exist to run safely, economically, along with constantly. Theoretically, good use and care of these components will assure years of operation that is good. Nevertheless, the real life is another story, in which motors are put through many environmental and operational risks that create winter pressure on the windings. Thermal stresses degrade the insulating material quality of the motor, therefore diminishing its life expectancy. That is exactly why checking the working condition of motors is now such an essential requirement of predictive maintenance programs.
For numerous years, maintenance as well as reliability engineers have been restricted to off-line or static testing of motors – determining a motor’s suitability for continued responsibility by making use of a handheld volt/ohm meter, clamp on ammeter, or maybe megohmmeter. But very often these tools started to be forensic devices used generally to identify what took place after the engine failed.
Although static testing is still a crucial part in checking & trending motor wellness, the techniques are restricted and are generally meant to explain insulation quality. Modern online test equipment helps the tech support in predicting imminent, insulation related failures. The first detection of these possible issues allows him to plan downtime and make scheduled maintenance over do emergency maintenance.
Online engine testing. Online or dynamic test equipment monitors motors in the organic surroundings of theirs. Dynamic testing offers details about power quality, the motor’s working quality, in addition to a huge quantity of info relevant to the load.
Modern test equipment collects data through 3 voltage probes and 3 corresponding present transformers, which are connected straight to the item of gear. More sophisticated equipment has the extra capability to gather information through permanently mounted gear located within the control box of low voltage motors or maybe the low voltage cabinet of high-voltage and medium- motors. When captured, the information will be calculated and translated through the test equipment and displayed for comparison, reporting, and also trending.
The data collection procedure is non intrusive, allowing the tech support to gather a great quantity of info without interrupting processes or operations. Besides being nonintrusive, the powerful tester can get, diagnose, store, and trend info within seconds. Next, the tech support is able to transport the information to a desktop PC for more analysis and sharing with some other maintenance personnel. Several aspects of concern like high temperature readings or maybe overvoltage situations, previously unavailable to most predictive maintenance personnel and also reliability technicians, are easily and also quickly shot and displayed with electronics based equipment.
5 important indicators. To fully evaluate a motor’s overall health, the tech support should be in a position to find out the total picture, which includes all points affecting the standard functioning of the motor. These aspects of concern are grouped in 5 main categories: power condition, working efficiency,, energy assessment and load, motor condition and motor performance.
Power quality. Incoming power quality is usually over looked by maintenance personnel, who generally just monitor and trend voltage levels. Nevertheless, power condition has a significant and real impact on the safe and proper operation of motors.
Voltage unbalances aren’t unusual, as well voltage levels change throughout the day. Some plant electricians believe larger voltages cause absolutely no actual harm to motors because the state enables lower present levels. They’ll essentially increase voltages to a quality which is going to bring the motor’s present down to nameplate scores, despite the fact that the engine is running above rated horsepower. This misconception is verified false because the ensuing iron saturation leads to extreme heat, in turn, which, degrades the insulating material rapidly. As is more developed and documented, lower voltages lead to increased currents and, once again, extra heat build up within the windings.
Power quality is impacted by harmonic distortion, much of that is produced by variable frequency drives. Modern equipment and plants work with many drives that produce some degree of harmonic distortion. A little quantity of voltage distortion leads to a bigger quantity of recent distortion, in turn, which, leads to today’s levels to increase. This increased present and distortion increases heating inside the windings of a motor, and that degrades its insulation and shortens its daily life. Plant life could certainly additionally be put through harmonic distortion from nearby sources outside their personal perimeters. For instance, additional facilities within the vicinity is able to ship harmonic problems upstream and, eventually onto the buss of its friends. In many cases, these distortions go undetected.
Engine performance. Tracking motor present levels and unbalances is a vital component of a great motor condition monitoring system. Sometimes it’s discovered that existing amount is identified as the average current quality for all phases. For predictive maintenance reasons, nonetheless, the greatest line present level created is of very much higher value. The heat in every motor winding is interdependent on the quantity of current which passes through it. Thus, probably the weakest point of the motor’s insulation with respect to present amount is definitely the stage with the biggest current.
Motors normally see 6 to ten times rated today’s levels during each start. Hot starts are a lot more damaging to the windings because the excessive heat produced during this time period leads to quick insulation degradation. Besides gathering and keeping the regular working data, contemporary dynamic test gear can shoot startup info, current, including voltage, and torque levels. This info displays the enormous stress to that a motor is subjected whenever it has going. Many motors fail during this particular startup period as a result of these stresses.
Motor quality. You are able to consider motor state as anything associated with a motor’s health. Rotor bar problems are a single problem that directly impacts the motor’s capacity to deal with its load. Rotor bar concerns have grown to be a key problem for reliability engineers, who spend a good deal of time checking out the recorded dynamic details related to this problem to be able to find and determine this particular problem. Rotors are put through significant stresses during startups, during fluctuating load circumstances, and also during power quality problems. Monitoring these stresses is of vital importance when figuring out a motor’s potential to keep in operation. Broken or even cracked rotor bars are accountable for losses in productivity and dramatic increases in winter stress.
Motor problem may additionally be described as changes in the method which impacts the working condition of the engine. Working condition is definitely the complicated signature of the motor responding to stuff and power conditions. Trending and tracking these circumstances provides proof that the motor’s earth has changed, and additional scrutiny of information is required.
Stuff and energy assessment. Load, percentage of load, kilowatt usage, horsepower demand, and strength factor are key elements concerning a motor’s health. Significant load fluctuations may possibly indicate a potential load related problem. Many motors remain operating within nameplate current ratings while being pressured to transport load demands above the capacity of theirs. These over the top load demands result in the windings to operate above a safe temperature level. Motors needed to run above nameplate horsepower ratings in addition are afflicted by higher torque demands, that inflict undo pressure on the motor’s rotor.
Dynamic test tools could be put in place to monitor torque information, which includes periodic changes and torque levels referred to as torque ripple. These torque signatures are obvious photographs of the load’s operational state and also offer insight into the stresses subjected on the motor’s rotor. Trending and monitoring torque as a characteristic of the daily operating condition of a motor is important when separating electrical concerns from mechanical issues. Bearing faults, variable-frequency-drive-related issues and numerous mechanical problems might be seen and diagnosed through the torque spectra.
Operating efficiency. The never ending initiatives to lower a plant’s cost of operations demands that facilities personnel intelligently monitor energy use and motor repair/replacement costs. Often motors were oversized or maybe undersized due to subsequent changes or incorrect engineering to a connected device. Oversized motors have larger initial costs and are usually much more expensive to fix and use. Undersized motors perform poorly and also are afflicted by higher losses, which causes them to fail much earlier than properly sized motors. Put simply, improperly sized motors are much less effective, and consequently much more expensive to use. Dynamic testing delivers adequate info about the motor’s general working setting to enable a skilled specialist to correctly assess the sizing of all replacement motors.
Summary of benefits. Dynamic motor testing is rapidly turning into an important component of all great predictive maintenance programs, as fresh innovations consistently be available in the form of both hardware along with program upgrades. It may be performed much more frequently and with no concern of interrupting some plant or processes operations. If not for the powerful test, numerous issues that create insulation degradation will be ignored.
The latest innovations in dynamic test equipment capabilities have enhanced their parameters, expectations, and horizons. Besides identifying electrically related trouble areas, lots of hardware problems may today be identified, such as bearing faults, imbalance, physical and mechanical looseness, then eccentricity.
All this ability offers help on the reliability engineer’s method of keeping a safe, effective, and effective operation. But simply gathering information isn’t adequate when managing a predictive maintenance program. As with any specialized field, good training and knowledge is needed for a reliability tech support to properly and successfully identify and utilize the powerful evaluation data. To be able to properly manage a vegetable or maybe facility motor reliability application, present day predictive maintenance personnel has to be highly trained, do probably the newest equipment, and stay within the academic loop.