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