DRIVE CAREFULLY and save the planet

Energy consumption in the process industries is easily identified, when it's being used to supply heat. Less apparent, but more costly, are the countless items of electrically driven equipment.

While it is easy to see where smelting, heating and so on can swallow energy, about two-thirds of all the electrical energy consumed by industry in industrialised nations is used to power electric motors.

The incorporation of variable speed drives in many applications within the process engineering sector - especially those involving motors used to power fans and pumps - can save significant amounts of energy. Moreover, it reduces the by-product of that electricity generation - harmful CO2 emissions.

Under the Framework Convention on Climate Change, signed by Britain and 150 other nations at the 1992 Rio Earth Summit, each nation agreed to reduce greenhouse gas emissions to 1990 levels by the year 2000. It is widely understood that if all ac electric motors were as efficient as today's best designed induction machines, the saving in electricity and its consequent CO2 emissions would be dramatic. If all electric motors were controlled so that their speed was governed and use was on demand, those savings would increase tenfold.

However, it's difficult to persuade the operator of a process plant 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 adequately.

Awareness of the energy issue relating to electric motors is set to rise, thanks in part to the efforts of ETSU (Energy Technology Support Unit), the now-privatised de facto UK national energy agency. ETSU is a government funded organisation which manages public and private energy programs.

ETSU has many roles in energy technology across the coal, solar, wind and wave power fields, and administers several government-launched best practice plans relating to energy. It also advises manufacturing companies that are reluctant to approach suppliers for information regarding the benefits of power management techniques. ETSU is also helping to increase understanding of the potential for variable speed controls with ac motors, by supporting the promotional efforts of drives companies.

The government, eager to encourage such 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.

Such initiatives have existed for some time in the US, where electricity consumption is a major issue. Spurred by these circumstances, drives companies active in North America have been quickest to bring energy efficient products to market.

Motor efficiency is only part of the problem. In 1995, a New Zealand energy consultant, John Banks, reported that the two most effective opportunities to save energy in motor drives are to match the motor and mechanical systems using variable speed controllers, and to optimise the process. The latter includes improving the efficiency of the driven load and the motor drive transmission. Banks estimated that the potential of these two opportunities for saving energy is more than six times the more traditional measure of improving motor efficiency - replacing the motor. And this applies irrespective of the motor's age or condition.

Apart from the savings any inverter can enable, many of the latest models incorporate specific energy-saving features. These range from being able to switch on and off on demand, to automatically tuning themselves to deliver optimum performance with any standard ac motor.

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 succeeds in its quest for better understanding of the technology and economics of drive usage.

Most of the major UK manufacturers and suppliers of variable speed drives are exhibiting at the forthcoming Drives and Controls Exhibition (16-19 March, Telford), as is ETSU. PE

John Houston is a writer on industrial and technology issues