Using motors and ancillary equipment that’s well designed and matched to the application can cut energy costs significantly.
In terms of potential energy savings, the best candidates on
a packaging line are the workhorse, analog, three-phase AC motors that power
main machinery components and conveyor driveshafts, along with their
accessories: the drives that feed them current and the gearboxes that convert
their shaft rotation into torque.
When it comes to energy consumption, it pays to be aware of
an important recent regulation governing AC motors.
Under the Energy Independence and Security Act, signed into
law in December 2007, general purpose electric motors of 1 to 200 horsepower
(HP) manufactured in the United States after 2010 have to meet an efficiency
standard known as NEMA Premium.
NEMA is the National Electrical Manufacturers Association, a
trade and standard-setting organization. The NEMA Premium standards for
electric motor efficiency, generally speaking, exceed the previous regulatory
standard by one to two percentage points. These motors cost about 15% to 20%
more than standard motors, but the energy savings often give a quick return on
investment. That situation applies to aftermarket motors replaced by end users
as well as those that come with original equipment.
The new regulation includes most AC motors on today’s
packaging lines-but there are exceptions. For example, if a motor is mounted to
a gearbox but doesn’t have a mounting base, it can legally operate at less than
the efficiency standards specified by the Energy Independence and Security Act.
Therefore, it can pay for a purchaser who is mindful of energy efficiency to
make sure that all motors on new equipment, even those that fall within EPAct
loopholes, meet the standard or are specified with NEMA Premium efficiency.
In many cases, end users find it more cost-effective to
repair motors instead of replacing them. When motors are repaired, they also
can have their energy efficiency enhanced.
End users can insist that repairs be done according to
ANSI/EASA (American National Standards Institute/Electrical Apparatus and
Services Association) standards. The most common repair option to improve
energy efficiency is rewinding the copper wire in the stator (the motor’s stationary
inner core). Switching to a traditional, hand-inserted lap winding and
increasing the slot fill (the overall amount of copper in the stator’s hollow
slots) can improve heat transfer and reduce copper loss and winding
temperature, improving the motor’s overall efficiency.
Power-transmission equipment also presents an opportunity
for energy savings. The most common such devices are gearboxes, also known as
speed reducers, which mechanically convert the rotation of a motor’s shaft into
torque that turns machine components or moves conveyor belts.
As with motors, more expensive equipment can lead to
long-term savings. Worm-gear speed reducers have been commonly used because
they have relatively few moving parts, which makes them inexpensive to buy and
maintain. The downside is that they can lose up to 50% of efficiency in
translating the motor’s power into torque. Devices like helical-gear reducers
are more expensive but can operate at up to 98% efficiency. For this reason,
worm-gear devices are being phased out, but some equipment manufacturers still
use them, either to save money or because their smaller size warrants their use
in a given machine.F&BP
April 30, 2008