Electric Motors

Flashcards contain key terms and definitions related to electric motors, covering their advantages, disadvantages, specifications, and operational parameters.

Electric Motor

An efficient means of converting electrical energy into mechanical energy.

Approximate Efficiency of EM

efficiencies ranging from 50-99%

Advantages of Electric Motors

Low initial cost, inexpensive to operate, fractional and integral horsepower sizes, easy to start, compact, low noise, no exhaust fumes, minimal safety hazards, potential for automatic control.

Disadvantages of Electric Motors

Not adapted to mobile applications, used only in farms with existing lines, affected by power outages.

Single-phase motors

The most common type of electric motors found in homes, farms, and light industry.

Locked-rotor Torque

Motor torque at zero speed or the maximum torque available to start the load.

Pull-up Torque

Lowest value of torque produced by the motor between zero and full load.

Full-load Torque

Torque necessary to produce the motor’s rated horsepower at rated speed.

Breakdown Torque

maximum torque a motor can carry

without an abrupt drop in speed that may make the

motor stall or be inoperative

what happens when temp of motor increases

both bearing and insulation life are reduced

40 degrees Celcius

Normal maximum ambient temperature for motor operation

Duty rating

Refers to how frequently the motor is started and how long it will run each time it is started

Continuous duty

Operated for more than 60 min

Intermittent duty

Operated for upto 30 min at a time and rest

Service Factor

Indicates the maximum load that can be carried by the motor while operating within a safe temperature range.

Wire Sizing

Wires must be sized to avoid voltage drop and should be able to carry 125% of the full-load current.

Motor Nameplate

Essential information about the motor, including manufacturer name, model number, horsepower, voltage, and current ratings.

Starting Current Requirements

a current of magnitude 2 to 7 times

larger than the full-load current is expected

NEMA

National Electrical Manufacturer’s Association

Motor code

Letter designating starting current requirement

Less than or equal to 2%

Allowable voltage drop of motor