EMSC

ELECTRIC MOTOR SERVICE CENTER Inc.  

 3565 Viaduct SW, Grandville, MI 48418

Phone: 616-532-6007

 

Getting the most from your Electric Motors

Maintenance: Proper maintenance and operation are the keys to getting the most from your general purpose electric motors and other electrical equipment. You should schedule routine preventive maintenance procedures at regular intervals. Routine maintenance should include lubrication, cleaning the inside and outside of your motor and electrical and mechanical testing. To be effective, each of these operations must be performed with accuracy and care.

Lubrication: Too much lubrication is a major cause of premature motor failure (PMF). If too much grease is applied, it is eventually forced out of the bearing housings and begins dripping on motor windings and internal switches. It then attacks and destroys the insulation system. To relubricate standard duty motors, follow the original manufacturer's specifications. Begin by cleaning the grease fitting and removing the drain plug. The best time to lube a motor is while it is at normal running temperature. Turn the motor shaft while installing lube to allow it to find it's "place" rather then pack into the bearing and jam or "stick" the balls. Run the motor for a while before installing the drain plug allowing the excess grease to purge out rather then leaking onto motor insulation. Clean off extra lube. If the motor manufacturer's specifications are not available use the following guide for lube replenishing: RPM Frame range 8 Hr./day service 24 Hr./day service 3600 56 - 256T 8 months 4 months 3600 284T - 286T 6 months 2 months 3600 324T - 587T 4 months 2 months 1800 56 - 256T 4 years 2 years 1800 284T - 326T 4 years 18 months 1800 364 - 365T 1 year 4 months 1800 404T- 449T 9 months 3 months 1800 505U - 587U 6 months 2 months 1200 or less 56 - 256T 4 years 2 years 1200 or less 284 - 326T 4 years 18 months 1200 or less 364T- 449T 1 year 4 months 1200 or less 505U - 587U 9 months 3 months If you can hear a ball bearing "squeal" then the damage is already done and replacement, rather then lubrication, is the proper solution.

Cleaning: It is very important that the air passages be kept clean so that the motor can dissipate the heat it develops by circulating cool fresh air through it. With totally enclosed-fan cooled motors, it is also necessary to keep the cooling fins free of dirt and debris, because these motors depend entirely on heat transfer through the fins to dissipate heat. To assure proper cooling, make certain nothing prevents sufficient amounts of fresh air from reaching your motors. Make sure that your motor is not recirculation the same hot air it pushed out because it's vents are placed to close to a wall or another motor and hot air can't escape.

CAUTION! As service personal you must fully understand electrical safety precautions and apply them during all phases of inspection, cleaning, testing and repair. KEEP AWAY FROM LIVE CIRCUITS! Lock and tag out all electrical circuits and test for voltage before touching anything. Electrical Testing: One of the most useful tests for determining when to remove a motor from service for overhaul or rewinding is the insulation resistance test. To be most effective, this test should be conducted at regular intervals with the results recorded for comparison with future readings. This is referred to as trending. Test the motor at room temperature with a megohm meter between the windings and the motor frame. For motors with voltage ratings of 2400 volts or less, use a 500-volt megohm meter. The resistance readings should trend in a straight line on a graph. If resistance drops for two or three successive tests, the motor should be scheduled and removed for service. NOTE: High humidity can cause resistance values to drop. Lower resistance readings from one test to another may reflect this condition and may not mean the insulation system is deteriorating.

Mechanical Testing: Vibration analysis is helpful in extending the useful life of a motor. By regular inspections for vibration, you can detect problems like bearing wear, mechanical looseness in machine fits, misalignment, defective belts or couplings, defective rotors and electrical unbalance, loose mounts and other things. Early detection of these problems can reduce the number of unscheduled shutdowns and prevent avoidable damage to your equipment while helping you pinpoint the source and probable cause of the trouble.

Predictive Maintenance: Regular, scheduled predictive maintenance can minimize unscheduled outages and downtime. This consists of plotting trends and test values ( ex: insulation resistance and vibration). By projecting test trends (trending) you can determine when corrective action will be necessary. This is also cost effective from a repair standpoint because scheduling jobs in a motor shop on regular time can save you the "time and a half" or over-time, rush charges.

Voltage Problems: Incorrect Voltage… One of the best ways to insure economical performance and long motor life is to make sure your motors operate at nameplate voltage. Applying too high a voltage may reduce the motor's efficiency and increase iron core losses. This shortens motor life by overheating the insulation system. Operating on too low a voltage reduces the motor's effective horsepower. (ex: a 5 HP motor operated 10% below rated voltage becomes a 4 HP) The motor will try to drive the load it was intended to drive but become overloaded, draw more current and overheat the insulation system causing motor failure. TIP: Get rid of the cheesy extension cords.

Unbalanced Voltages… Operating a three phase motor with unbalanced voltage or on an open-delta distribution system can also cause serious overheating that will shorten motor life dramatically. You can determine the amount of overheating with this formula: 2x (% voltage unbalance squared) = percent of additional temperature rise. Example: A motor with a 3.5% voltage unbalance will experience an additional temp. rise of approximately 25% above its rated temp. rise (2 x 3.5squared = 25). A standard, totally enclosed, fan cooled T-frame motor has a temperature rise of about 75 degrees C. An increase of 25% would raise the operating temp. about 19 degrees C (75 x .25 = 18.75) Generally speaking, each 10 degrees C rise above the rated temperature cuts motor life by half. An increase of 20 degrees C would reduce motor life by about one-fourth of normal. This condition can be addressed using motors with higher temperature insulation systems. Motors generally have a class "B" insulation system rated at 130 degrees C. If you use motor with a higher rated insulation system class, like class "F" rated at 155 degrees C, you raise the "Service Factor" and get longer life with the same voltage problems. Motor Application tips: Be sure you use the right motor for the application. For instance, in an application that requires high starting torque; a 3 phase, general purpose, NEMA Design B or single phase PSC motor might be inadequate. A NEMA Design C, 3 phase motor or a capacitor start, single phase motor that has more starting torque may be required.

(For more information request an "Electric Motor Engineering Handbook" from EASA)

Continuous-Duty motors should not be used in applications that require frequent starting or reversing unless special provisions are made. These motors must be allowed to run long enough after each start to dissipate the heat that builds up from the "inrush" current (about six times the rated full load current) that surges through the windings during the starting period.

Avoid "plug-stopping" (stopping a motor by electrically reversing it) when frequent stops and starts are required. Plug-stopping develops three times more heat in a motor then starting does. If frequent stops are required, consider using an electro-mechanical braking/clutch devise.

Keep motors dry. Moisture greatly shortens motor life because it can deteriorate the insulation and create electrical paths to the motor frame or electrical ground. To prevent condensation you can try electric space heaters in your motor or apply a low DC voltage to one phase of the motor windings whenever the motor is at rest. With either method, the objective is to keep the temperature of the windings 5 to 10 degrees C warmer then ambient temperature. Make sure they turn off while motor is operating to avoid motor overheating.

Installation: Proper shaft alignment and mechanical placement are vital to the successful operation of your motor. Also make sure all electrical connections are tight and properly insulated. Run your new motor uncoupled for a few minutes and check direction of rotation and no-load current. No-load current is about a third to a half of full load current and is higher in slower speed motors. Lock out and tag out the voltage control and couple the motor to the load. Rotate the shaft manually to be sure there is no binding in the drive or other problems with the load. This is a good time to take vibration readings to be sure the drives are aligned and also to establish a base line for future readings.

Spare Motors: Having a spare motor can keep down time to a minimum especially for motors that are vital to your operation. Store your spare motor in a clean, dry area and rotate the shafts periodically to keep lubricant on the bearings.

Replace or repair?  If you're thinking replacement consider an energy-efficient motor for applications requiring near full output on continuous loads. The term energy-efficient covers a wide range of efficiencies so carefully check all of the manufacturer's actual ratings. How long can you be with out this motor? If it's that critical to your operation should you get the new one and repair the old one for a spare? Repairing a motor often has advantages over replacement. Some adaptation costs can be high on special mounts so repairing the original motor can save these costs. In most cases, the insulation system in a rewound motor will have a higher temperature rating which will extend the life or the motor. Feel free to discuss any motor in question with us at the Electric Motor Service Center.

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Open Monday - Friday 7:00am to 5:00pm

Mike Dertien  ~   Adam Dertien  ~  Sam Dertien