As energy costs rise, manufacturers are now, more than ever, looking for strategies to cut their energy usage. According to the U.S. Department of Energy, electric motor-driven machinery uses more than two-thirds of all electricity in industry. Due to tough economic conditions, companies may be holding off replacing older motors with more efficient designs. However, it’s important to remember that any motor upgrade should be evaluated by its life-cycle cost rather than its purchase price. Recent studies show the initial cost of an industrial AC electric motor is less than five percent of its life-cycle cost, with energy making up more than 95 percent.

System review for
maximum savings
Looking beyond simple motor replacement and analyzing the system will generally provide more savings.

For example, if a right-angle worm speed reducer is used, changing to an in-line helical (ILH) or right-angle helical bevel (RHB) reducer will have a significant impact on raising efficiencies, especially when paired with NEMA Premium efficient motors.

Helical gearing technology delivers a wide range of ratios while maintaining 98-percent efficiency per stage of reduction. Helical-bevel, right-angle gearing technology delivers efficiencies of up to 95 percent. Conversely, a single-stage worm gear reducer’s efficiency can be as low as 60 percent.

The reason helical gearing is more efficient is a result of how the torque is transmitted through a rolling action. For a worm gear, torque is transmitted through a sliding action between the worm and the worm gear. This sliding action causes considerable friction and heat, which leads to greater efficiency loss than other types of gearing.

The overall system efficiency of the motor and gearbox is the product of the individual efficiency of each item. With worm gear reducers, efficiency is lost at each stage of reduction. Although upgrading to a premium efficient motor provides some benefit, the maximum energy efficiency can only be seen by pairing the helical reducer with a premium efficient motor.

An additional benefit of replacing the gearbox can be seen by the total load of a particular system. The gearbox accounts for part of the total load seen by the motor. As an example, for a 1.0-HP motor that is seeing total loading of 1.0 HP, if the gearbox being used is 80 percent efficient, the actual load itself is only 0.8 HP (the other 0.2 HP is required for the gearbox).

If the gearbox is switched to a 95-percent efficient model, for the same system, the total load now required by the motor is 0.8 HP / 0.95 efficiency = 0.842 HP (15.8 percent less HP required). Using the same assumptions as earlier, and assuming 85-percent motor efficiency (not changed) for the calculation, yields the following results:

• Annual electrical cost with old gearbox: 
{(1.0 HP)(0.746 kW/HP)(7200 hrs/yr)(0.1 kW/hr)}/85% = $631.91

• Annual electrical cost with new gearbox:
{(0.842 HP)(0.746 kW/HP)(7200 hrs/yr)(0.1 kW/hr)}/85% = $532.06

So the cost of the old minus the cost of the new ($631.91 - $532.06) equals $99.85 saved annually.

The overall cost savings in the last column is a factor of the efficiency gain of the motor, efficiency gain of the gearbox, as well as reduced electrical usage required by the motor. Analyzing the motor/gearbox combination and choosing both NEMA Premium efficient motors and high efficiency helical gearing is the best solution for keeping energy costs to a minimum.

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Mike Fulton is a Baldor industry engineer for food, beverage and pharmaceutical. For more information, visit www.baldor.com.