Electrical Motor Selection & Maintenance Quiz

Electrical Motor Selection & Maintenance

• Objectives: Identify components for motor selection, explore maintenance techniques, and identify motor replacement information.

Major Motor Types

• Alternating Current (AC) motors:
  • Single-phase motors
  • Polyphase (three-phase) motors (require three-phase service).
• Direct Current (DC) motors:
  • Ideal for variable speed control.
  • Used when AC is unavailable.

End Bells & Enclosures

• Open enclosure:
  • Motor casting and ends are vented
  • Outside air cools the windings.
  • Less expensive.
• Totally enclosed:
  • Motor casting and ends are enclosed.
  • Prevents outside air (wet, flammable, corrosive, dirty) from entering the motor.

External Features

• Open enclosure
• Totally enclosed

External Features Mounting

• Solid, rigid base: Motor mount is part of the motor casting.
• Resilient base:
  • Mount is separate from the motor.
  • Resilient rings absorb vibration and noise.
  • Conductor attached to complete grounding.

Internal Features Shaft

• Shaft is a round rod protruding through the motor center.
• Responsible for power output.
• Keyed shaft and threaded shaft types must be considered.

Internal Features Sleeve Bearing

• Brass, bronze, or tin-lined cylinder.
• Mounted parallel to the floor.
• End shield may need rotating to prevent oil spill issues.
• Used where low noise is important.

Internal Features Ball Bearing

• Round steel balls in a special cage surround the shaft.
• Can be mounted in any position.
• Used when high shaft load capacity is needed.

Mechanical Considerations Drives

• Types of direct drives:
  • Flexible hose coupling drive: Plastic or rubber hose as the drive.
  • Flange coupling: Two metal discs and a flexible middle disc; “flange” attaches to motor, other to equipment.
  • Cushion-flange coupling: Tire-shaped cushion between flanges.
  • Flexible shaft: Used for operating at various angles (e.g., grinders, buffers).
• Gear drives & Chain & sprocket drives

Mechanical Considerations Pulley & Belt Drive

• Often used in farming.
• Larger pulleys offer reduced slippage.
  • Standard V pulley
  • V-step pulley
  • Adjustable V pulley

Mechanical Considerations Types of Pulleys

• V-belt:
  • Motor mounted closer to machine.
  • Belt stays on better.
  • Webbed multi V-belt: Two or more V-belts webbed together; eliminates slippage, belt turnover.
• Flat belt: Requires flat pulley on motor and machine.
• V-flat: One or more V-belts, one V-pulley and one flat pulley.

Electrical Considerations Voltage

• Common 60Hz voltages:
  • Single-phase motors: 115V, 230V, 115/230V
  • Three-phase motors: 230V, 460V, 230/460V

Electrical Considerations Current (Amps)

• Measures current flow.
• Capacitor stores electrical energy and blocks current flow.
• Capacitor starts motor and assists primary windings' speed attainment.

Electrical Considerations Hertz Frequency

• Hertz measures electrical frequency (cycles per second).
• North America: 60Hz
• All other countries: 50Hz

Electrical Considerations Horsepower (HP)

• Measures work rate.
• 746 watts = 1 HP (at 100% capacity).
• Watts x % capacity = 746 or 1 HP.

Electrical Considerations Torque

• Force applied to a shaft.
• Usually expressed in inch-pounds.
• Torque = distance × weight.
• "Twisted force".
• Torque Types:
  • Starting (locked rotor) torque: Force from standstill to acceleration.
  • Full-load torque: Force while running at rated horsepower and full-load speed.
  • Breakdown (pull-out) torque: Maximum torque a motor can produce without speed drop due to load increase.
  • Pull-up torque: Minimum torque when increasing from zero RPM.

Motor Controls

• Manual, semi-automatic, and automatic controls protect motors from overheating.
• Functions: Limiting inrush, reversing the motor, controlling speed, and acting as a brake.
• Types of switches: Pushbutton, toggle, snap action (with/without overload protection).

Overload Protection Thermal Protection (Overload)

• Built-in overload protection: Automatic reset (power restored once cooled). Unexpected starts can be hazardous. Manual reset (external button; for applications like saws and conveyors where unexpected starts are hazardous).
• Resistance temperature detectors(RTD): Resistors mounted onto machines used with heat detection instruments.

Replacement Factors

• Nameplate data
• Motor type
• Mechanical construction
• Electrical and performance characteristics.

Replacement Name Plate Data

• Most important step in the process.
• Record name plate information (saves time, avoids confusion, prevents misapplications)
• Name Plate Data to Record:
  • Type (AC or DC)
  • Phase (single or three)
  • Horsepower (HP)
  • Rotations per minute (RPM)
  • Duty (e.g., 15, 20, continuous)
  • Code (current required for start)

Maintenance

• Properly selected and installed motors operate for many years with little maintenance.
• Disconnect power before servicing.
• Clean motor surfaces and ventilation openings (dust and lint) to prevent overheating and failure.

Maintenance Lubrication

• Essential maintenance type.
• Consult operator manuals.
• Excessive/frequent lubrication damages motors.
• Adhere to motor-supplied instructions.
• Avoid mixing petroleum and silicone grease in motor bearings.

Maintenance Bearings

• Sleeve bearings: Use SAE 20 non-detergent or electrical motor oil. Avoid over-oiling; wipe off excess.
• Ball bearings: Hand-packed bearings need disassembly and greasing every 2-5 years.
• Special fittings bearings require bottom plug removal for greasing.

Acknowledgements

• Credits for multiple sources of information used in creating these notes. (Note: Specific acknowledgments are included in the original OCR.)