From component efficiency to system efficiency in variable speed motor drives

Panel: 4. Technology, products and systems

Authors:
Norbert Hanigovszki, Danfoss Drives A/S, Denmark
Aksel Jepsen, Danfoss Drives A/S, Denmark

Abstract

Motor systems have a large potential for energy savings, as they use approximately 65% of the electricity consumed in the European Union. In the recent years there have been a number of political initiatives to improve the efficiency of motor drive systems. These initiatives all address efficiency at component level, like motors, pumps and fans.

We are looking into three practical examples to assess the savings potential at three stages: component level, use of variable speed and system level. The baseline is an existing ventilation system with a 22 kW motor, 20 years old, with 3900 operating hours yearly and a defined duty cycle. Upgrading to a new IE3 motor will lead to an annual energy use of 90770 kWh, a saving of 6%. If the ventilation system is retrofitted with a frequency converter and high-efficiency IE4 motor, the annual energy use will fall to 26271 kWh, a saving of 72% – not unusual in retrofit applications!

For illustrating the advantages of system level optimization we will present the case of Marselisborg wastewater treatment plant (Denmark) which has turned from an electricity consumer to an electricity producer with 30% net annual surplus. System level optimization can give the highest energy savings, and there are some key elements within motor drive technology which make this possible:

– Freedom of choice to combine frequency converters with the right motor technology for the specific application (induction motor, PM, Synchronous reluctance)

– Open availability of efficiency data, also in part load conditions, to be used in optimal system design

– Use of energy optimized motor control is key to harvest the efficiency potential of electric motors

– Authorities and regulators are encouraged to focus less on component efficiency and more on system efficiency in legislation and regulation.