chapter 2
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
