Electric motor efficiency depends upon power factor - Part 1

Electric motor power efficiency has taken center stage. Individuals, corporations, and governments are increasingly interested in saving power, now that technology can make it possible and economy demands it. Advances in motor control algorithms and cost-effective electronic components for implementing motor drives are creating a revolution in virtually every electric motor market. Control of the power factor in an efficient manner also means less lost energy, both in the motor and drive electronics, and in the power grids supplying the electricity to the homes, offices, and factories where the motors are used.

Potential Savings

The potential energy savings are staggering. Over 40 million electric motors are used in manufacturing operations in the United States alone.1 Electric motors account for 65 to 70 percent of industrial electrical energy consumption and approximately 57 percent of all electrical consumption worldwide.2 Saving even a few percent of the world's estimated 16,000-plus terawatt-hours (TWh) annual consumption of electricity amounts to several hundreds of trillions of watt-hours per year. Currently, the average motor in use today has an efficiency of 88 percent in converting electrical into mechanical energy. Figures on the order of 96 percent conversion efficiency are technically feasible for larger motors.

For comparison, the electrical generation capacity of photovoltaic solar cells in all of Europe, where both Germany and Spain currently lead the US in installed base, is projected to be only 15 TWh/yr in 2010. In the UK alone, with an annual total electrical consumption of approximately 350 TWh, the Institute of Engineering and Technology estimated that 5 TWh could be saved annually through the use of more efficient electric motors. Furthermore, many motors are not used in an efficient manner. For example, the motor may be oversized for the job at hand, or much of its mechanical output power may be wasted, meaning that additional savings may come from how the motor is used, on top of the savings from the motor itself. In 1996, the United States Department of Energy speculated on savings of 5 TWh per year by 2000, and a 100 TWh per year savings potential by 2010,6 considering both motor and related system-level savings.

The potential is there to make significant advances in the next few years as older motors and drives are replaced by newer more efficient ones. Because of the cost savings in electricity, many industries are voluntarily accelerating the turnover of their installed motor base, even replacing motors before they wear out. This is because the payback for the newer, more efficient motors and drives can be realized in less than a year and usually less than two years. Great strides are already being made. In the UK, for instance, sales of the least efficient motors, grade Eff3, have dropped from 68 to 8 percent between 1997 and 2004. During the same period, sales of the most efficient grade (Eff1) have increased from 2 to 7 percent, and further jumped to 17 percent in 2006, with the middle grade (Eff2) making up the balance of sales.