About two thirds of all the electrical energy consumed by industry is used to power electric motors. This is a figure that is mirrored in most industrialised nations. The incorporation of variable speed drives in many applications can save significant amounts of energy and reduce the by-product of that electricity generation CO2.
Under the Framework Convention on Climate Change, signed by Britain and 150 other nations at the 1992 Earth Summit in Rio de Janeiro, each nation’s goal was to take voluntary actions to reduce greenhouse gas emissions to their 1990 levels by the year 2000. It is widely understood that if all electric motors in use around the world were as efficient as the best designed machines available now, the saving in electricity and consequently reduction of CO2 in the atmosphere would be dramatic. If all electric motors were controlled to the point that their speed was governed and use was on demand, those savings magnify manyfold. It is therefore a fact that most drive Systems benefit from the incorporation of AC inverters, but the greatest savings are where varying demand is met by constant motor operation, such as in many fan and pump applications.
That said, it is a difficult task to persuade factories using thousands of motors on fans, pumps, compressors and the like that it is a worthwhile investment retrofitting even the lowest priced of presently available inverters. That is especially true if the drive is to be fitted to an ageing, and inexpensive, motor which appears to be running just fine.
Awareness of the energy issue relating to electric motors is set to rise, thanks in part to the efforts of ETSU. The de facto UK national energy agency, ETSU is a government funded company dedicated to managing public and private energy programs. ETSU has many roles in energy technology, across the coal, solar, wind and wave power fields and is responsible for administering a number of Government-launched energy related best practice plans, including the Energy Efficiency scheme. It also acts as an advisory Unit to manufacturing companies who are reluctant to approach suppliers for information regarding the benefits of power management techniques such as the installation of variable speed drives. ETSU is also helping to increase understanding of the potential for variable speed controls used with AC motors by supporting the promotional efforts of qualifying drives companies.
The government, eager to encourage such power management ideas, is prepared to offer financial incentives to companies undertaking innovative and wholesale overhauls of their power use, and ETSU assesses any new initiatives on an individual basis before putting them forward to government.
Under the Energy Efficiency scheme, AC drives companies can now qualify to use the nationally promoted ‘Energy Efficiency’ labels that were seen in a recent campaign of TV commercials focused on domestic heating Systems. Whilst the logo cannot be applied to the products themselves, since they may not always be applied in energy saving situations, it can be used in the promotion of drives for fans and pumps.
These sorts of initiatives have existed for some time in the USA, where electricity consumption is a major issue for industry. Spurred by these circumstances, drives companies that are active in the North American markets have been quickest to bring to market energy efficient products. The EpAct initiative has already put in place minimum standards for motor efficiency that must be adhered to by anyone making or selling motors in North America.
Motor efficiency is only part of the problem. In New Zealand in 1995 an energy consultant named John Banks reported that the two most effective opportunities to save energy in motor drives are to better match the motor and mechanical systems using variable speed controllers; and to optimise the process which includes improving the efficiency of the driven load and the motor drive transmission. Banks estimates that the potential of these two opportunities for saving energy is more than six times the more traditional measure of improving motor efficiency. In other words, irrespective of the age or condition of a motor, in many circumstances fitting a correctly rated inverter will save more energy than replacing the motor. Naturally, the best option is to do both.
The prime industries where energy savings can be achieved using VSDs are iron, steel and non-ferrous metals manufacture; wood, pulp and paper processing; and food and beverage processing. It is estimated that these industries account for more than 80% of power consumed through motor drives. Pumps and fans are the predominant loads in these sectors with motors usually over 7.5kW.
Apart from the savings any inverter can enable, increasing numbers of the latest models incorporate specific energy saving features. These range from being able to switch on and off on demand, automatically tune themselves to deliver optimum performance with any standard AC motor and to ramp speeds up and down according to varying loads.
Much has been written about the growth of AC inverters in recent years but this is largely thanks to the increased use of small drives for control purposes Use of these drives for energy saving is a huge and relatively untapped market. That may not be the case for much longer if ETSU and the UK’s drives industry succeed in their quest for better understanding of the technology and economics of drive usage.
Most of the key players in the variable speed drives market can be seen at the Drives and Controls Exhibition, as can ETSU which is also exhibiting at the show. Those interested in learning more about the services ETSU has to offer should call 01235 432361.