Electrical Motor Selection & Maintenance PDF

 Objectives To identify components influencing motor selection To explore proper maintenance techniques for electrical motors To identify proper information needed for motor replacement 2  Major Motor Types Alternating curr...

 Objectives To identify components influencing motor selection To explore proper maintenance techniques for electrical motors To identify proper information needed for motor replacement 2  Major Motor Types Alternating current (AC) motors − single phase motors − polyphase (three phase) motors must have three phase service Direct current (DC) motors − ideal for variable speed control − also used when AC is not available 3  End Bells & Enclosures Open enclosure − motor casting and ends are vented − outside air passes over the windings for cooling − less expensive Totally enclosed − motor casting and ends are enclosed − prevents outside air from entering the motor − used in wet, flammable, corrosive, and dirty environments 4  External Features Open enclosure Totally enclosed 5  External Features Mounting Solid, rigid base − mount is part of the motor casting Resilient base − mount is separate from motor − resilient rings absorb vibration and noise − conductor is attached to complete grounding 6  Internal Features Shaft A shaft is a round rod protruding through the center of the motor The shaft is responsible for power output Shaft types must be considered in motor selection − keyed shaft − threaded shaft 7  Internal Features Sleeve Bearing Brass, bronze or tin-lined cylinder Should be mounted parallel to the floor End shield may need to be rotated to prevent oil from running out of the reservoir Used where low noise levels are important 8  Internal Features Ball Bearing Round steel balls surround the shaft in a special cage May be mounted in any position Used when there is a need for high shaft load capacity 9 Mechanical Considerations Drives Types of direct drives Flexible hose coupling drive − a piece of plastic or rubber hose is used as the drive Flange coupling − two metal discs and flexible middle disc are components of this type − “flange” attaches to motor, another attaches to equipment and each attach to the flexible middle disc, allowing all to fasten together 10 Mechanical Considerations Drives Cushion-flange coupling − tire-shaped cushion between flanges 11 Mechanical Considerations Drives Flexible shaft − utilized in those situations where operating at various angles is necessary − direction of rotation is important because one must buy the shaft accordingly example: grinders and buffers 12  Mechanical Considerations Conversion Drives Gear drive Chain and sprocket drive 13 Mechanical Considerations Pulley & Belt Drive Most often used on the farm Less slippage occurs with larger pulley Types of pulleys include: − standard V pulley − v-step pulley − adjustable V pulley 14  Mechanical Considerations Types of Pulleys V-belt − motor can be mounted closer to the machine − belt stays on the pulley better Webbed multi v-belt − two or more v-belts webbed together − eliminates slippage and belt turnover 15  Mechanical Considerations Types of Pulleys Flat belt − must have flat pulley on the motor as well as on the machine V-flat − one or more v-belts − one v-pulley and one flat pulley 16  Electrical Considerations Voltage Common 60hz voltages for: Single phase motors − 115 volt, 230 volt, 115/230 volt Three phase motors − 230 volt, 460 volt, 230/460 volt 17  Electrical Considerations Current (Amps) Amperage measures current flow − capacitor stores electrical energy and blocks current flow − capacitor starts motor and aids primary windings in reaching operational speeds 18  Electrical Considerations Hertz Frequency Hertz is the measurement of electrical frequency (cycles per second) North America − 60hz All other countries − 50hz 19  Electrical Considerations Horsepower (HP) Measures rate of work 746 watts = 1HP at full capacity (100%) Watts x % capacity = 746 or 1HP 20  Electrical Considerations Torque Force applied to a shaft Usually expressed in inch X pounds Torque = distance X weight “Twisted force” 21  Electrical Considerations Torque Types Starting torque (locked rotor torque) − force produced from standstill to acceleration Full load torque − force produced while running at rated horsepower and full-load speed Breakdown torque (pull-out torque) − maximum torque a motor will develop under increasing load conditions without an abrupt drop in speed and power Pull-up torque − minimum torque delivered between zero and rpm 22  Motor Controls Manual, semiautomatic, automatic controls protect motors against overheating 23  Motor Controls Functions To limit inrush To reverse the motor To control motor speed To act as a break 24  Motor Controls Types of Switches Pushbutton Toggle Snap action with/without overload protections 25  Overload Protection Thermal Protection (Overload) Built-in overload protection: Automatic reset − automatically restores power to engine once it cools − unexpected starting can be hazardous Manual reset − external button restores power − use where unexpected starting is hazardous − saws, conveyors, etc. 26  Overload Protection Thermal Protection (Overload) Resistance temperature detectors: − resistors are mounted onto machine − used in conjunction with heat detecting instruments 27  Replacement Factors Name plate data Motor type Mechanical construction Electrical and performance characteristics 28 Replacement Name Plate Data The most important step in replacement process Recording name plate information: − saves time − avoids confusion − prevents misapplication 29 Replacement Important Name Plate Data Type (AC or DC) Phase (single or three) Hp (horsepower) Rpm (rotations per minute) Duty (15, 20, continuous, etc.) Code (current required for start) 30  Maintenance Properly selected and installed motors are capable of operating for many years with a small amount of maintenance Power must be disconnected before servicing Clean motor surfaces and ventilation openings periodically of dust and lint to avoid overheating and failure 31  Maintenance Lubrication Most necessary type of maintenance Always consult an operator manual before service Excessive or frequent lubrication may damage motor Follow instructions furnished with motor Do not mix petroleum grease and silicone grease in motor bearings 32  Maintenance Bearings Sleeve bearings use SAE 20 non-detergent or electrical motor oil Do not over oil and wipe off excess Ball bearings Hand-packed bearings need to be disassembled and packed with grease every two to five years Special fittings bearings need bottom plug removed before greasing 33  Acknowledgements Glossary of Electric Motor Terms. Electrical Motor Warehouse. 3 May 2002. http://www.electricmotorwarehouse.com/Glossary.htm Selecting Pulley Types. 1998. Phoenix Manufacturing Company. 5 May 2002. http://www.Phoenix-mfg.com/service.htm. Technical Reference Guide. 1996-2001. Leeson Products. 3 May 2002. http://www.leeson.com/products/tehref/maintenance.htm Bear & Hoerner. (1983). Electric Motors. Minnesota: Hobar Publications. 34  Acknowledgements Production Coordinator Garry Powers Graphic Designer Melody Rowell Technical Writer Jessica Odom V.P. of Brand Management Clayton Franklin © MMXIV CEV Multimedia, Ltd. 35