Type of Electric Motors
The motor's bearings
Allow for low-restriction rotation of the rotor. They help reduce friction and the heat generated by the motor's moving and rubbing parts and surfaces.
Motors
Are rated with two different current ratings, full-load or rated-load amperes (LRA) or rated-load amperes (FLA or RLA).
Motor slip%=
Calculated motor speed-actual motor speed/calculated motor speed x 100
S (rpm)=
Frequency * 120/ number of poles
Motor Slip
Represents the difference between the motor's calculated and actual speed.
Is not wired to the power source like the stator is
Rotor
The Starting and Running Characteristics
Two major considerations of electric motor applications
Magnets
are known to have two different electrical poles, north and south. Unlike poles attract each other, and like poles repel each other.
Electricity and magnetism
are used to create the rotation in an electric motor to drive the fans, pumps, and compressors.
Excessive motor slip
can be an indication of improper motor lubrication, defective motor bearings, poorly adjusted belts (too tight), or an improperly selected motor for the desired application (overload)
Capillary Tubes Applications
can typically use compressors with low starting torque as a the system pressures can equalize during the off cycle.
Single-Phase Motor
has two run windings and one start winding. The two run windings have the same resistance and the start winding has a high resistance.
Start Windings
have more turns than the run windings and are wound with smaller diameter wire.
Motor Housing, End Bells, and Base
hold the motor components in place and provide a means for securely mounting the motor itself.
The Stator
is a winding that, when energized, will generate a magnetic field-because there will be current flowing through it.
Typically, the LRA for a motor
is about 5 times the FLA/RLA.
The Motor Shaft
is connected to the rotor; therefore, when the rotor turns, so does it.
Start Winding
is in the circuit only for as long as it takes the rotor to get close to its rated speed and it then is electrically disconnected.
Slip
is often expressed in percentage.
Locked-rotor amperage
is often referred to as inrush current.
RPM
is rotation per minute.
Starting Torque
is the power to turn the shaft from the stopped position.
The Rotor
is the rotating portion of the motor and is made of iron or copper bars bound on the ends with aluminum.
Synchronous speed
is the rpm of a motor without a load.
Torque
is the twisting power of the motor shaft.
Start Winding
is wound next to the run winding but is a few electrical degrees out of phase with run winding.
When a motor is still
it takes a great deal of torque to get it turning, particularly if the motor has a load on start-up.
Split-Phase Motors
many have fours poles and run at 1800 rpm.
Some Motors
must have a great deal of starting torque and to turn the motor at the stopped position but do not need a great deal of torque to maintain speed.
A motor applied to a refrigeration compressor
must have a high starting torque, it must be able to start under heavy starting loads.
The Motor
must have enough torque to operate with the load of the application.
Some TXV systems
require greater starting torque as there may be a pressure differential across the compressor even when the compressor is not operating.
