Page 54 - Energize September 2021 HR

TECHNICAL

Efficiency of electric motor

driven systems

by Mike Rycroft, Now Media

According to the International Energy Agency (IEA), electric motors are responsible for 53% of the world’s
total electricity consumption, and 70% of industrial energy consumption. A small reduction in energy
usage from motors could make a huge difference to total energy consumption.

esearch has shown that the upfront cost and maintenance The efficiency of an EMDS (such as a pump, fan, compressor
of a motor is less than 5% of the total lifetime cost, the other or industrial handling and processing) is determined by the total
R95% is electricity. Reducing the electricity cost significantly system, i.e., the multiplication of efficiencies for each component.
reduces the lifecycle cost. Within the various electric motor technologies that are in use,
Electric motors consume energy. Controlling the operation energy‐savings options are available for both components and
of an electric motor by means of a drive can substantially integrated systems. Figure 2 gives an illustration of the savings
improve efficiency and result in a consequent reduction in energy possible for an EMDS.
consumption. To focus on the efficiency of the motor alone
overlooks opportunities to improve the overall efficiency of the
electric motor driven system (EMDS), which can be substantially
more than that of the motor alone.

Electric motor driven systems
An electric motor driven system (EDMS) comprises four layers of
equipment:
1. A fully functioning electric motor driven from the supply.
2. The motor together with its drive and sensing equipment,
referred to as the power drive system (PDS). The motor and
drive may be supplied as a matched unit.
3. The extended motor system (EMP) or core motor system,
comprising the PDS and its driven piece of mechanical
equipment (fan or pump wheel, compressor, etc.) plus the
Figure 2: Savings possible for an EMDS 2
necessary interconnection (clutch, gear, transmission belt) and a
variable‐speed drive (VSD) system between the electrical supply
and the motor to control torque and speed. Overall, using the best available motors will typically save about
4. The system: The eventual application of power (a water 4% to 5% of all electric motor energy consumption. Linking these
heating piping system, an air ventilation ducting system, a motors with electromechanical solutions which have been cost‐
cooling system with its cold-water network and the cooling optimised for the end‐user will typically save another 15% to 25%.
tower, a compressed air pipe system and the storage The potential exists to cost‐effectively improve energy efficiency of
tank, a conveyor belt installation, an elevator for people or motor systems by roughly 20% to 30%, which would reduce total
3
goods, etc.). global electricity demand by about 10%. The three major ways of
achieving these savings are:
• Use of properly sized and energy‐efficient motors
• Use of variable speed drives, where appropriate, to match motor
speed and torque to the system mechanical load requirements.
This makes it possible to replace inefficient throttling devices
and, in some cases with “direct‐drive”, to avoid wasteful
mechanical transmissions and gears.
• Optimisation of the complete system, including correctly sized
motor, pipes and ducts, efficient gears and transmissions,
and efficient end‐use equipment (fans, pumps, compressors,
traction, and industrial handling and processing systems) to
Figure 1: Components of an electric motor driven system (EMDS) deliver the required energy service with minimal energy losses.

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