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SERIES 21 / Module 08 Drives & Motors


Making motors and drives efficient


Adetunji Lawal, head of energy and carbon, Wates Group Limited


A


n electric motor is a device that converts electrical energy to rotary kinetic (movement) energy to power


a process. Examples of processes include HVAC fans and pumps, washing machines, and conveyor belts. Motors are found in a vast majority of equipment in our everyday life.


Scale of motor energy consumption Electric motive power is likely to form a large part of an organisation’s energy consumption, especially as a typical motor will consume energy ten times its purchase cost over its lifetime. Motor use is significant in the UK, Europe and indeed across the world. In the UK fans use approximately


40% of all electricity in HVAC systems. In the USA, electric motor-driven


systems and components in appliances and equipment account for more than 25% of the primary energy consumption in both residential and commercial sectors . In Europe, there are over 8 billion


electric motors in use and the appliances they power consume almost 50% of the electricity generation. In industry, machines driven by electric motors consume about two thirds of all electrical


AC motor


energy. They are found in machines such as elevators, cranes and cooling systems. More efficient motors could save EU member states around 110 TWh of energy savings annually by 2030, equivalent to the electricity consumption of Netherlands. This means 40 million tonnes of CO2 emissions per year is avoided.


How do motors work? When an electrical current is applied to the motor, a rotating magnetic field is created around the stator. This induces currents and associated magnetic fields in the rotor, causing the rotor and shaft to spin. The shaft is mounted on bearings and is thus able to rotate freely. There are three main types of


motors: direct current (DC) motors, alternating current (AC) motors and electronically commutated (EC). DC motors convert direct current


electrical energy into mechanical energy. There are two main types of DC motors: brushed and brushless. AC motors are generally classified


into synchronous and induction motors. When viewed from the electrical input, induction motors are single-phase or 3-phase induction motors. Single phase motors generally move small loads but can suffer up to a 10% loss in efficiency compared


to three-phase motors used in commercial buildings. Electronically commutated (EC)


motors are essentially brushless DC motors with permanent magnet and built in electronics that control the torque and speed of the motor. Electronically commutated motors are now widely used in the lower power categories due to their higher efficiency performance especially at part-load conditions. Motors can range in size/scale from


small motors for a remote control car to very large industrial shredder motors; small motors having an input of <0.75 kW, to large motors rated at >375 kW. Electric drives are normally


classified into three groups, namely individual, group and multi motor drives. If a single motor is used to drive or


actuate a given mechanism and it does all the work connected with this load, it is called an individual drive. When groups of machines are organised on one shaft and driven or actuated by one motor, the system is called a group drive or line shaft drive. This can be economical overall as a single large capacity motor often costs less than multiple small motors. A multi-motor drive consists of


several individual motors which serve many mechanisms in production applications. This type of drive finds its application in complicated machine tools, travelling cranes, rolling mills, etc. For example, in a travelling crane


three motors are used, one for hoisting, another for long travel motion and third for cross travel motion.


For details on how to obtain your Energy Institute CPD Certificate, see ENTRY FORM and details on page 22


EIBI | MARCH 2024


How is a motor's effi ciency defi ned? Electrical motor efficiency is the ratio between shaft output power and electrical input power. If power output is measured in Watts


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EIBI | OCTOBER 2022


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