In the drive for energy efficiency motors matter most

Increasingly stringent international regulations, rising energy costs and concerns over CO2 emissions are key drivers of efforts to improve manufacturing efficiency in both new and existing plants.  In some installations, savings of 60-70% can be realised and return-on-investment achieved in months, rather than years. Motors and pumps account for well over half of a plant’s energy consumption in many instances, so these are often at the heart of developing a strategy and plan to measure and minimize the energy used at every point in the process. The main areas to be considered are shown below.

Effective power factor correction improves supply quality from the grid. This is an important consideration in AC drives and in AC-DC power supplies. Adding power factor correction capacitors, such as PP film types from Epcos, to inductive loads like motors provides a modest improvement in energy efficiency but may deliver significant cost savings where power utilities impose a low power factor penalty in their rate structure. Automatic power factor correction systems that switch capacitors in and out under varying load conditions may also be adopted.

For measuring power consumption, wireless power meters offer a quick and easy retrofit option because the need for additional cabling is minimised. A comprehensive range of conventional and wireless meters, from 13 suppliers, is available from RS. These include products from ABB, Merlin Gerin and Schneider Electric.

Both DC and AC variable speed drives (VSD) have become more efficient in recent years, primarily due to advances in power semiconductors. Today, some single phase AC drives now boast efficiencies of 95% or more. ABB, Allen Bradley, Mitsubishi, Omron, Parker, Schneider Electric and Siemens are among the leading vendors of high-efficiency motors, drives and controls. RS offers both single and 3-phase drives, plus a selection of own-brand DC servomotor controllers for the lower power end of the spectrum.

While normally associated with pumps and motors, VSDs can also be used to improve the efficiency of pneumatic systems. Pneumatics are estimated to use 10 to 15% of the electrical energy in a typical manufacturing plant and controlling the air supply so that it varies precisely with demand can produce direct energy savings up to 30% in some installations. Of course, selecting the right size motor for the task is one of the most important considerations in optimising system efficiency.

European standard EN 60034-30:2009 defines legislative requirements for the efficiency of 3-phase motors in the 0.75 to 375kW range (2, 4 and 6 pole). Such motors have had to reach IE2 High Efficiency standards since 16th June 2011 and from January 2015 must meet IE3 Premium Efficiency. Advances in motor design, improvements in bearing technology, and intelligent motor control are the primary factors that lead to improvements in motor efficiency. For example, SKF deep groove bearings for electric motor rebuilds exhibit 30-50% less frictional losses than other SKF bearings. This extends bearing life and improves efficiency without going to the expense of replacing the complete motor. ABB offers a good selection of 3-phase motors in its M3 family and both Panasonic and Parvalux are popular choices for single-phase applications.

With respect to AC-DC power supplies used to provide the correct operating conditions for electronics systems in a plant, efficiencies have risen from some 80% to up to 95% in the past few years. However, it is worth noting that manufacturers tend to quote efficiency figures at full load. Power supplies may operate much less efficiently at lower loads, so it is worth ensuring that the efficiency profile of the selected power supply matches the real-world application. RS markets well over 1000 models of high-efficiency AC-DC power supplies from leading brands including Astec, Mean Well and Power-One.

Of course, plant maintenance has a major impact on overall energy efficiency, particularly with respect to transmission systems. There is limited value in efficiently powering a rusty drive chain! RS can help here too, with a comprehensive range of facility maintenance products and equipment.