Copper and Motor Efficiency .pdf
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Copper and Motor Efficiency
Key words: motor copper,copper motor,copper rotor motor,copper wire
motor,copper coil motor,motor efficiency,electric motor efficiency,induction
motor efficiency,motor losses,stator and rotor,motor stator
What’s Motor Efficiency?
Motors convert electrical power(input power) into mechanical power(output
power). All motors have stator and rotor. When an electric current flows
through, the magnetic field produced by the stator rotates, causing the rotor to
rotate. Since the rotor is fixed to the shaft, the shaft also rotates. For an electric
motor, efficiency is the ratio of mechanical power output to the electrical power
Stator and Rotor Conductors
For a motor, either the stator or the rotor can be permanent magnet. When the
stator is an electromagnent instead of a permanent magnent, it will be a field
coil or field winding, made of either copper or aluminum.
For an induction motor, the rotor can be either wound type or squirrel-cage
type. A wound-rotor motor has a rotor winding made of insulated wire. A
squirrel-cage rotor is composed of conductive bars and end rings commonly
made of copper or die cast aluminum. Almost 95% of the induction motors
used is of squirrel cage type.
Electric motors experience various losses during power conversion, including
magnetic core losses(iron losses), friction and windage losses(mechanical
losses), stator resistance losses, rotor resistance losses, and stray load losses.
Losses reduce the efficiency of the machine and usually result in unwanted
Stator and rotor I2R losses, also called copper losses, are major losses in
motors. They are caused by current flowing through stator and rotor
conductors. Reducing stator and rotor losses can improve motor efficiency.
Importance of Improving Efficiency
* High efficiency cuts the operating costs. Even one-point rise in efficiency can
result in massive savings in the motor’s service life.
* Improving efficiency contributes to energy saving and reduces gas emissions.
By reducing energy loss, we can reduce the consumption of fossil fuels used to
produce electricity, thus reducing emissions of CO2.
Use More Copper for Higher Efficiency
Since stator and rotor losses are I2R losses, losses reduction can be achieved
by decreasing R(resistance).
The stator coil can be either copper or aluminum, while copper coils are the
norm due to its high electrical conductivity. To reduce stator loss, one can
increasing the cross-sectional area of the copper conductors to decrease
Aluminum is also used for stator coils for its lower cost. As aluminum has a
much lower electrical conductivity, it requires a cross-section that is much
Squirrel cage rotors are commonly made of copper or die cast aluminum. To
reduce rotor losses, one can increase the size of rotor conductive bars and
Motor Stator Recycling Equipment
Companies can recover copper from motors that are no longer in use. While
you may think it is labor intensive, there are machines that special designed for
recycling copper windings from motor stator. The equipment involves a copper
wire cutting machine and copper wire pulling machine. The former is used to
cut one end of the copper windings in the stator, while the latter is used to pull
the windings out.