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great a sacrifice of efficiency via core loss, and too great a burden
of copper loss through impaired permeability. The possibility of
obtaining grain texture and orientation should not be ruled out, bringing
additional benefits.
This excess consumption is not only an unnecessary burden on the
energy bill, but it damages the equipment and motor as the excess
energy released is through the winding and core of the motor in the
form of heat, vibration and noise.
Power electronics in induction electric motor
efficient operation
There are VFD systems that not only vary the frequency, and therefore
the speed, but have facilities to monitor the load and adjust the voltage
to optimise the power usage.
VFD operation of induction motors gives a number of benefits in
power saving as they are able to optimise and control the speed of
the driven equipment. There are other benefits that can be obtained
by controlling the input voltage to the motor because of this unique
characteristic of ac induction motors.
• Reducing speed eliminates the necessity of throttling and wasting
power
• Reducing voltage moves the PF curve to the left resulting in
reduced current, reduced current due to the improved power
factor and reduced voltage reduced I
2
R losses (copper losses)
• Reducing voltage reduces flux density in the iron (laminations)
reducing iron loss
• VFD systems reduce the stresses on the motor as they are
effective soft start devices. The low frequency start controls the
current and torque produced by the motor which results in low
current and not the six to 10 times starting current found in DOL
motor starting systems
• Mechanically this is beneficial as there is no shock load applied
to the mechanical system such as coupling, shafts and load
Transmission lines and the distribution system
In the early days of commercial electric power, transmission of electric
power at the same voltage as used by lighting and mechanical loads
restricted the distance between generating plant and consumers.
In 1882, generation was dc, which could not easily be increased in
voltage for long-distance transmission. Different classes of load (for
example, lighting, fixed motors, and traction and railway systems) re-
quired different voltages, and so used different generators and circuits.
When the ac systemwas introduced, transformers developed that
enabled voltages to be increased and decreased as required assisting
in facilitating transmission over long distances.
Losses in transmission line are related to I
2
R so reducing the
current reduces the losses proportionally to the square of the current
whereas the power is proportional to the product of voltage and current.
1
Electro technology
– at well over 100 years old –
is due for a radical breakthrough.
The sky’s no longer the limit!
13
ENERGY EFFICIENCY MADE SIMPLE 2015