chapter 2

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dc series motor

develops 500% of its full-load torque at starting. this motor is used in applications where large amounts of starting torque are needed

squirrel cage motor

enclosed motor, due to the absence of any moving electrical contacts they are suitable for use where they are exposed to flammable dust or gas

...

exposed live parts must be guarded if operating at 50 volts

dc motor

feild poles are the stationary magnet

wound rotor induction motor

frequent starts without overheating. limited starting current

FLA

full load amps is noted on nameplate indicating the current the motor will draw at nameplate horsepower frequency and voltage

Copacitor-start motor

gives its motor a starting torque of about 4 times its rated torque. highest starting torque.

capacitor start motor

high starting torque

dc compound motor

high starting torque and constant speed under load

variable -torque load

horsepower varies approximately as the cube of the speed and the torque fairies approximately as the square of the speed

name plate

information for motor

DC injection breaking

is a method of braking in which direct current(DC) is applied to the stationary windings of an AC motor after the AC voltage is removed.

weather protected motors

is minimizing exposure to the elements

rotating magnetic field

is the principal of both induction and synchronous motor

depending on how the stator is wound

it may have 2,4, or any even number of poles.

Shaded Pole Motor

low starting torque, low efficiency, and high noise level.

shaded pole motor

low starting, low efficiency, high noise

...

nec requires disconnecting needs be in sight

P

number of magnetic poles

Dynamic Braking

of a DC motor maybe needed because DC motors are often used for lifting and moving heavy loads that may be difficult to stop.

Field Poles

produces a magnetic field

Split-phase Motor

produces a starting torque of about one to two times its rated torque

rpm

rated full load speed is the value indicated in rpm on the nameplate

Alternating Current (AC)

reverses between positive and negative polarities and varies in amplitude with time.

...

speed goes up, frequency up. poles up, speed down.

N

speed in rpm

Self Inductance

the ability of a conductor to induce voltage in itself when the current changes.

inductance

the characteristics of an circuit that opposes the change of current flow.

slip

the difference in rotation speed between the rotor and the stators magnetic fieldin an induction motor

Frequency

the frequency of a waveform is the number of times per second an identical pattern repeats itself.

constant-torque load

the torque remains constant throughout the speed range, and the horsepower increases and decreases in direct proportion to the speed

Hertz (Hz)

the unit of frequency. one Hz equals one cycle per second(cps)

due to the absence of moving electrical contacts

they are suitable for use where they are exposed to flammable dust or gas

totally enclosed motor type

water-cooled

open motor type

weather-protected (type l & type ll)

frequency

determines the speed of ac motor

Synchronous speed

120f/p

Synchronous motor

A three phase motor that operates at synchronous speed from no load conditions to full load conditions

Sine Wave Generation

An electric current in a conductor creates a magnetic field that surrounds the conductor

NEC Article 430

Covers the application and installation of motors, motor controls, and motor circuit connections including conductors circuit and ground fault protection starters, and overload protection.

dynamic braking

Of a DC motor may be needed because DC motors are often used for lifting and moving heavy loads that may be difficult to stop. for example, forklifts often use dynamic braking

# of motor nema designated

abcdf , 5 motors

weather protection

according to NEMA is an open motor

dc motor

best choice for adjustable motor

field winding and armeture

can vary the speed on a dc shunt motor

reverse motor

change two connections

speed

constant torque load is directly proportionat to speed


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