Pumps & Systems - September 2007

Improving Motor Life Cycle Costs
Efficiency and
Your Bottom Line
Getting to the Meaning
Behind the Nameplate
John Engman, Emerson Motor Company
Because operational costs ride on efficiency determinations, accurate
measurements of losses occurring within the motor are paramount. The reliability
of efficiency data is key to any energy-savings plan, and knowing the meaning
behind the rating can make or break a smart purchasing decision.

Whether you are a municipality or an industrial facility, you know that operating costs are one of management’s biggest concerns when considering how to power your pumping system.

So, now that you have convinced management to lower costs by purchasing a premium efficient motor, what’s next? It’s time to ensure you’re really getting that efficiency rating you purchased.

The topic of efficiency has been a mainstay in industrial circles since the Energy Policy Act went into effect in 1997, requiring motors to meet minimum efficiency standards. Facilities using highly efficient systems are taking advantage of costs savings on their utility bills and positively contributing to the bottom lines – real financial returns for an industry the U.S. Department of Energy estimates consumes more than $30 billion a year in electricity to power motorized systems.

While the DOE provides a wealth of information on what industrial facilities can do to maximize efficiency, the only way to obtain a reliable figure for operational-cost purposes is to measure it.

In technical terms, efficiency is a ratio of energy watts out to energy watts in. Watts in are determined by measuring the losses occurring in the motor’s stator winding, rotor or iron, as well as by friction and windage. The more mysterious stray losses that occur within the motor are also taken

into account when determining efficiency.

Because operational costs are riding on efficiency determinations, accurate measurements of losses occurring within the motor are paramount.

To measure these losses, IEEE 112 helps motor manufacturers determine efficiency ratings by approving several methods of measuring motor losses. Motor manufacturers typically use two methods for a majority of motor efficiency testing today.

For variable loads like fans and pumps, the most popular motor designs follow the NEMA design class B guideline for speed and torque characteristics. For these machines, IEEE 112 Method B is commonly considered the preferred method of testing. This method uses a carefully calibrated dynamometer to measure the motor’s power and torque – key components of determining efficiency percentages.

However, larger horsepower motors (500-hp and above) require substantial electrical power systems and load cells to run performance testing, making the dynamometer an impractical option for some manufacturers. In these instances, testers use IEEE 112 Method F, an equivalent circuit methodology based on calculations and assumptions.