"Smart" electric motors could save a hydroelectric power plant
Atle Kjærvik
"By replacing or rebuilding thousands of ordinary electric motors, which are used in pumps, refrigeration and ventilation units, in order to turn them into speed-controlled motors, we could save one TWh of energy (equivalent to the output of the controversial Alta hydroelectric plant in Northern Norway)," says Professor Tore M. Undeland of NTH.
NTH's Dept. of Electrical Power Engineering lays great importance on providing training in the problems of speed control of electric motors. Graduate student Jan Hystad is becoming a specialist in motor control systems
Most industrial and domestic electric motors in use today have been designed to run at more or less constant speeds. Many of them are overdimensioned, perform unnecessary work and thus waste energy. Only a small proportion of these motors are speed controlled. "Smart" motors of this type use only as much energy as they require to do their job. "This is where their energy-saving potential lies hidden," Undeland points out.
Large savings to be made
It is estimated that in the USA, 60 - 65% of industrial energy consumption goes into running electric motors. There are no comparable figures for Norway, but if we look at industrial electricity consumption, we find that the aluminium industry uses about 200 GWh a year on electric fans alone. The equivalent figures for the paper and chemical industries are about 180 and 110 GWh respectively. If we assume that the rest of industry operates at about the same level as the USA, i.e. that about 60% of the energy used goes to electric motors, the ventilation market alone accounts for some 500 GWh, or 10% of the Norwegian market."These figures are so large that even a single percent reduction would be a considerable saving."
"Intelligent" electric motors
The most important difference between an ordinary electric motor and a speed-controlled motor is that the latter is fitted with an electronic control unit which supplies the motor with as much energy as it needs. It carefully allocates energy in step with requirements. The control unit can thus be compared with an automatic gas pedal."The asynchronous motor (induction motor) is the most common type of industrial electric motor. It is cheaper and more robust than other types of motors. At the Dept. of Electrical Power Engineering we have therefore placed importance on developing systems for speed control of asynchronous motors. Rapid developments in power electronics and microprocessors have made it possible to develop cheap "mini-brains" or converters that are capable of meeting industrial standards of precision and acceleration. In a lift, for example, such a converter can apportion energy according to the weight the lift is carrying, giving more gentle starts and stops. "Smart" electric motors can also be coupled to systems that recover energy on the way down. The problem has been that converters have produced both acoustic and radio noise and have interfered with other electronics in their vicinity. We are now in the process of solving these problems," says Undeland.