project maker
08-08-2014, 10:27 AM
Efficiency trends in electric machines and
drives
[attachment=66727]
Abstract
The key challenges to increased efficiency in systems driven by electrical machines
lie in three areas: firstly, to extend the application areas of variable-speed electric
drives through reduction of power electronic and control costs: secondly, to integrate
the drive and the driven load to maximise system efficiency: finally, to increase the
efficiency of the electrical drive itself.
By adopting known, proven concepts it is possible to dramatically increase the
efficiency of systems driven by electrical machines and reduce total electricity
consumption by over 7%. Some of this improvement arises from the efficiency of the
machine, but the majority is due to the improved system efficiency, which can be
achieved with a variable-speed drive.
Almost all electricity in the UK is generated by rotating electrical generators, and
approximately half of that generated is used to drive electrical motors. Hence,
efficiency improvements with electrical machines can have a very large impact on
energy consumption. In the short to medium term, efficiency gains within electrical
machines will result from the development of new materials and construction
techniques.
Approximately one-quarter of new electrical machines are driven by variable-speed
drives. These are a less mature product than electrical machines and should
therefore see larger efficiency gains over the next 50 years. Advances will occur, with
new types of power electronic devices that reduce switching and conduction loss.
With variable-speed drives, there is complete freedom to vary the speed of the driven
load. If fixed-speed machines were replaced with variable-speed drives, for a high
proportion of industrial loads, this could give 15–30% energy savings. The potential
efficiency improvements within the driven load are projected to save the UK 15 billion
kWh per annum which, when combined with the motor and drive efficiency gains,
amount to a total annual saving of 24 billion kWh.
Introduction
Electrical machines have advanced significantly in recent years due to the
introduction of new materials. New electrical steels have reduced losses and rarearth permanent magnet materials have provided a 'lossless' source of magnetic flux.
Recent advances in construction methods have reduced winding losses, so there is a
continued trend to increase efficiency. For large electrical machines, efficiency is
already high and so, although significant, the potential gains are limited. Greater
gains are possible in smaller machines, which may be only 50% efficient.
Variable-speed drives are created when a motor is combined with a power electronic
converter. By introducing variable speed to the driven load, it is possible to optimise
the efficiency of the entire system and it is in this area that the greatest efficiency
gains are possible.
This paper has three main sections – one covering the statistics of energy
consumption and current predictions of possible savings using existing technology; a
second covering the current state of the science, and a final one on future, more
long-sighted possibilities.
Current state of the science
Industrial motor systems are dominated by induction motors running at effectively
constant speed. Variable-speed drives, in which the speed of the machine is
controlled by a power electronic converter, are taking an increasing size of the
market and in 2004 accounted for 25% of new systems (de Almeida et al. 2005). The
efficiency of the electrical system in isolation will first be considered, before
progressing to the entire system where, with the addition of variable-speed drives,
much larger energy savings can be made.
Generation
Large turbogenerators of 100–660 MW rating supply the vast majority of the UK's
electricity. These are wound rotor synchronous machines whose efficiency is over
98%. The very high efficiency arises by virtue of their very large size, with designs
only changing marginally in the last few decades as newer, low-loss materials
emerge.
There is much more diversity in electricity generation from renewable resources.
Most wind generators are doubly-fed induction machines, fed through a step-up
gearbox, but direct-drive permanent magnet generators are emerging as an
alternative. With direct-drive permanent magnet systems, the efficiency of the
generator is increased, and the gearbox losses are eliminated, but additional power
electronic converter losses are introduced, and the system costs rise due to the large
mass of the low-speed generator.
CONCLUSIONS
By adopting known, proven concepts, it is possible to dramatically increase the
efficiency of systems driven by electrical machines and reduce total electricity
consumption by over 7%. There is a trend for increasing efficiency within the
electrical machine itself, but the greatest gains are at system level when the machine
is combined with a power electronic converter to create a variable-speed drive. The
main barriers to this lie in the initial cost of a variable-speed drive, even though in
many cases the payback period is short. Future advances in technology will reduce
the capital cost of the drive, and so existing markets will grow and new markets open
up. In the future, electric drives will become integral to the propulsion of road
transport vehicles, so the need for maximising their efficiency will become even more
pressing than it is today.
drives
[attachment=66727]
Abstract
The key challenges to increased efficiency in systems driven by electrical machines
lie in three areas: firstly, to extend the application areas of variable-speed electric
drives through reduction of power electronic and control costs: secondly, to integrate
the drive and the driven load to maximise system efficiency: finally, to increase the
efficiency of the electrical drive itself.
By adopting known, proven concepts it is possible to dramatically increase the
efficiency of systems driven by electrical machines and reduce total electricity
consumption by over 7%. Some of this improvement arises from the efficiency of the
machine, but the majority is due to the improved system efficiency, which can be
achieved with a variable-speed drive.
Almost all electricity in the UK is generated by rotating electrical generators, and
approximately half of that generated is used to drive electrical motors. Hence,
efficiency improvements with electrical machines can have a very large impact on
energy consumption. In the short to medium term, efficiency gains within electrical
machines will result from the development of new materials and construction
techniques.
Approximately one-quarter of new electrical machines are driven by variable-speed
drives. These are a less mature product than electrical machines and should
therefore see larger efficiency gains over the next 50 years. Advances will occur, with
new types of power electronic devices that reduce switching and conduction loss.
With variable-speed drives, there is complete freedom to vary the speed of the driven
load. If fixed-speed machines were replaced with variable-speed drives, for a high
proportion of industrial loads, this could give 15–30% energy savings. The potential
efficiency improvements within the driven load are projected to save the UK 15 billion
kWh per annum which, when combined with the motor and drive efficiency gains,
amount to a total annual saving of 24 billion kWh.
Introduction
Electrical machines have advanced significantly in recent years due to the
introduction of new materials. New electrical steels have reduced losses and rarearth permanent magnet materials have provided a 'lossless' source of magnetic flux.
Recent advances in construction methods have reduced winding losses, so there is a
continued trend to increase efficiency. For large electrical machines, efficiency is
already high and so, although significant, the potential gains are limited. Greater
gains are possible in smaller machines, which may be only 50% efficient.
Variable-speed drives are created when a motor is combined with a power electronic
converter. By introducing variable speed to the driven load, it is possible to optimise
the efficiency of the entire system and it is in this area that the greatest efficiency
gains are possible.
This paper has three main sections – one covering the statistics of energy
consumption and current predictions of possible savings using existing technology; a
second covering the current state of the science, and a final one on future, more
long-sighted possibilities.
Current state of the science
Industrial motor systems are dominated by induction motors running at effectively
constant speed. Variable-speed drives, in which the speed of the machine is
controlled by a power electronic converter, are taking an increasing size of the
market and in 2004 accounted for 25% of new systems (de Almeida et al. 2005). The
efficiency of the electrical system in isolation will first be considered, before
progressing to the entire system where, with the addition of variable-speed drives,
much larger energy savings can be made.
Generation
Large turbogenerators of 100–660 MW rating supply the vast majority of the UK's
electricity. These are wound rotor synchronous machines whose efficiency is over
98%. The very high efficiency arises by virtue of their very large size, with designs
only changing marginally in the last few decades as newer, low-loss materials
emerge.
There is much more diversity in electricity generation from renewable resources.
Most wind generators are doubly-fed induction machines, fed through a step-up
gearbox, but direct-drive permanent magnet generators are emerging as an
alternative. With direct-drive permanent magnet systems, the efficiency of the
generator is increased, and the gearbox losses are eliminated, but additional power
electronic converter losses are introduced, and the system costs rise due to the large
mass of the low-speed generator.
CONCLUSIONS
By adopting known, proven concepts, it is possible to dramatically increase the
efficiency of systems driven by electrical machines and reduce total electricity
consumption by over 7%. There is a trend for increasing efficiency within the
electrical machine itself, but the greatest gains are at system level when the machine
is combined with a power electronic converter to create a variable-speed drive. The
main barriers to this lie in the initial cost of a variable-speed drive, even though in
many cases the payback period is short. Future advances in technology will reduce
the capital cost of the drive, and so existing markets will grow and new markets open
up. In the future, electric drives will become integral to the propulsion of road
transport vehicles, so the need for maximising their efficiency will become even more
pressing than it is today.