Process Efficiency Includes Motors

When your latest high-priority process design project gets into full swing, several objectives must be met. Product yields must hit high levels. Product quality must provide a competitive advantage. You must minimize process cycle times, whether batch or continuous, to improve overall throughput. Last, but hardly least, you must control product costs to ensure acceptable profit margins.

The first line of defense in cost control usually is raw materials, since they often represent the largest component of total cost. System automation also is a strong cost-controlling element and can contribute to rapid recipe changeover, better accuracy and subsequently improved equipment usage.

Energy consumption also can be a significant part of the total cost. However, more often than not, it is considered in the context of steam generation, compressed air production and heat-transfer requirements. Energy should not be treated as an expense, but as a raw material that can be managed. With wise management and the addition of premium-efficient motors, your processing plant's uptime also might be improved.

As you analyze every cost element, it makes sense to evaluate a frequently overlooked source of inefficiency: the electric motors driving the process equipment. The cost impact of electric motors includes much more than initial purchase or rewind price.

You should evaluate the purchase of electric motors and drives on life-cycle cost ," not initial purchase price. In today's competitive market, chemical processors are concerned about eliminating downtime, but also recognize the need to operate motors using the least amount of energy.

Now is the time to consider investing in motors and drives upgrades.

Source: U.S. Department of Energy

It comes as a surprise to many users that the initial purchase price of an electric motor generally is only 2 percent to 4 percent of its lifetime operating cost (Fig. 1). Many equipment manufacturers sell in a very competitive market and often do not or cannot differentiate equipment by cost of operation. Purchase price usually is the only issue. Higher-efficiency motors and drives would add value to the equipment and ensure lower operating costs over the equipment's life.

According to a 1998 study by the U.S. Department of Energy, the typical life of an AC motor is 28 years. When a company considers life-cycle costs, it often looks no further than a return on invested capital for the motor. Most companies seek a 2-3 year payback. With motors lasting far longer, they continue to save money throughout the operating lifetime.

The National Electrical Manufacturers Association (NEMA) first made a distinction between standard and energy-efficient motors in September 1990. The "energy-efficient" motor efficiencies later became standards for the Energy Policy Act of 1994 (EPAct).

In October 1997, EPAct took effect, mandating minimum efficiency levels for general-purpose totally enclosed, fan-cooled (TEFC) or open drip-proof (ODP) 1 horsepower (hp) - 200 hp (0.75 kilowatt [kW] - 150 kW) two-, four-, six- and eight-pole foot-mounted motors. The act requires any EPAct motor sold in the United States to comply with minimum nominal efficiency, testing and labeling standards. EPAct does not cover special-purpose motors such as footless motors with C-faces, pump mountings or other non-standard mountings.

In 1996, the Consortium for Energy Efficiency (CEE) established premium-efficiency guidelines, used by many utilities for rebate programs. In mid-2001, NEMA and CEE harmonized their efficiency standards, establishing NEMA Premium efficiency standards for ODP and TEFC 1 hp - 500 hp (0.75 kW - 370 kW) two-, four- and six-pole motors in low and medium voltage. The NEMA Premium standard first defined in NEMA MG1-1998, Rev. 2 does not differentiate between mounting configurations, and covers all types of motors.

Source: U.S. Department of Energy

The No. 1 failure mode for electric motors is the bearing system. Ideally, motors that comply with the IEEE 841 standard will provide additional protection, resulting in reduced downtime without the need for the specifier to write a custom proprietary motor specification. By specifying a motor that complies with this standard (IEEE 841-2001 Standard for Petroleum and Chemical Industry ," Severe Duty Totally Enclosed Fan-Cooled (TEFC) Squirrel Cage Induction Motors ," Up to and Including 370 kW [500 hp]) the user gets a motor available from stock, designed and manufactured to a proven standard. The user could even upgrade the IEEE 841-2001 motor by specifying a motor with NEMA Premium efficiency, resulting in lower operating costs.

IEEE 841 covers 1 hp- 500 hp (0.75 kW - 370 kW) TEFC two-, four-, six- and eight-pole motors. With the adoption of IEEE 841-2001, minimum nominal efficiency was set up slightly better than EPAct. The previous 841 (1994) standard was set at EPAct levels. The nominal efficiencies of motors from most manufacturers comply with NEMA Premium. It is expected that the NEMA Premium efficiency levels will be the new minimums for the next revision of IEEE 841.