DRIVES, MOTORS + SWITCHGEAR
I
n recent years the majority of emphasis has been on the improve-
ments which have been made in electric motor efficiency, in part
due to the changing regulations which have focusedmanufacturers
and customers alike. However, in terms of overall efficiency within
drive systems which are powered by electric motors, the mechanical
system also needs to be considered as it possesses a very significant
potential for optimisation.
In between the electric motor and the final process there is usually
a series of mechanical drives, gears, couplings and bearings which
transmit the mechanical power supplied by the motor. By examining
each component within this mechanical section and optimising the
design, further efficiencies and savings can be made.
Improved motor efficiency
It is well known that electrical motors use 65% of the energy used
in industry, but a lesser known fact is that 96% of the lifetime costs
of an electric motor is associated with the energy consumption.
This shows the importance of the overall efficiency compared to the
initial purchase cost in the terms of importance of the total cost of
ownership (TCO).
PMSM (Permanent Magnet Synchronous Motors) already fulfil
the requirements of the soon-to-be-implemented IE4 (Super Premium
Efficiency) classification. This is evidenced by their potential to achieve
energy savings of up to 40% compared to an IE2 inverter- driven squir-
rel cage motor. PMSM's offer considerably improved efficiency when
compared to inductionmotors even under partial load conditions; and
extremely high efficiency under rated operating conditions. They also
have considerably higher power density, which, for geared motors,
yields higher system efficiency with minimal installation volume
The synchronous design of the PMSMs means that not only are
they superior at converting electrical energy into mechanical power,
but they also offer the added benefit of maintaining constant speed
independent of the load. This means that motor speed does not vary,
despite overload variations, or cases of voltage drop, as long as the
mains frequency is kept constant. This design offers a number of key
benefits. It reduces heat losses from the rotor by 100%, total losses
by approximately 25%, and increases total efficiency by 10% or more.
For the PMSM user, this improved performance translates into lower
total cost of ownership, a reduction in CO
2
emissions, and ongoing
savings that buffer against future increases in energy costs.
The low operating and maintenance costs of the PMSMs mean
that they provide the optimum energy saving drive for use on fans,
pumps and compressors; and for constant torque applications such
as elevators and conveyors.
From January 2015 onward, energy efficiency class IE3 (Premium
Efficiency) will be the standard for motors with rated power of 7,5 to
375 kW, and from January 2017 onward for motors with rated power
Motor and drive efficiency –
collective approach for
better results
By M Kutny, Bauer Gear Motor
Efficiency, reliability and total cost of ownership are terms that are at the forefront of engineering considerations, however looking at items of
equipment on an individual basis may not deliver the maximum benefits.
The improved performance of a PMSM translates into a lower total cost of
ownership, a reduction in CO
2
emissions and ongoing savings.
Electricity+Control
July ‘14
20
