Produced in Association with


SERIES 21 / Module 08 Drives & Motors


(W) then efficiency can be expressed as: ηm = Pout / Pin where ηm = motor efficiency Pout = shaft power out (Watt, W) Pin = electric power in to the motor (Watt, W) The efficiency of electric motors


is different depending on the type of the motor. It is higher in high-power machines and lower in the low-power ones. It usually varies between 75% and 95%. While 100% efficiency is desirable,


its useful to understand how efficiency losses occur in motors from a variety of sources: ● Copper losses – this is electrical


power lost in the primary rotor and secondary stator winding which is from resistance. ● Iron losses – they occur as a result


of magnetic energy dissipated when the motor's magnetic field is applied to the stator core. ● Mechanical losses – includes


friction in the motor bearings and the fan for air cooling. ● Stray losses – these are the


losses that remain after primary copper and secondary losses, iron losses and mechanical losses. The largest contribution to the stray losses is harmonic energies generated when the motor operates under load. These energies are dissipated as currents in the copper winding, harmonic flux components in the iron parts, and leakage in the laminate core. In general, as motor power


increases, the efficiency of the motor at full load also increases. This is partially due to the difficulty in dissipating heat in smaller motors. Higher power motors also operate close to peak efficiency for a wide range of loading conditions.


Regulatory view on motors? The International Electrotechnical Commission (IEC) has published an international standard that defines


UK legislation for motor energy efficiency Date


1 July 2021 1 July 2021 1 July 2023 1 July 2023


1 July 2023 Motor Range


0.12 kW to 0.75 kW 0.75 kW to 1000 kW 0.12 kW to 1000 kW >0.12 kW


75 kW to 200 kW UK Minimum Efficiency Standard


IE2 (except if Ex eb increased safety motors) IE3 (except if Ex eb increased safety motors) IE2 for Ex eb increased safety motors IE2 for Single-phase motors


IE4 for 2, 4, or 6 pole 3-phase motors (except for brake motors, Ex eb increased safety motors & other explosion protected motors)


Produced in Association with Figure 1


Chevrolet Bolt. The power of a vehicle’s electric


motor, as in other vehicles, is measured in kilowatts (kW). 100 kW is roughly equal to 134 horsepower, but electric motors can deliver their maximum torque over a wide RPM range. This means that the performance of a vehicle with a 100 kW electric motor exceeds that of a vehicle with a 100 kW internal combustion engine, which can only deliver its maximum torque within a limited range of engine speed. Energy is lost during the process


5 distinct energy efficiency classes for single-speed, three-phase motors (IE1, IE2, IE3, IE4 and IE5). This standard has also been adopted as a European and UK Standard (BS EN 60034-30:2014). Using the graph in Figure 1, it can be


seen that an IE1 10kW motor is around 86% efficient and an IE5 10kW motor is around 95% efficient. Therefore changing an older pump with IE5 motors can result in 10% energy savings and a 25% reduction in payback time. The UK, in recognition of energy


use associated with motors, has set energy-efficiency legislation (statutory Instrument 2021/745). This ensures that motors sold in the UK from 2023 are minimum IE2 efficiency.


Motors in electric vehicles An electric car is an automobile that is propelled by one or more electric motors, using energy stored in


Power path in an electric car


rechargeable batteries. Globally, electric cars are witnessing rising growth, a development only made possible by advances in motor technology alongside battery technology. In practice, electric vehicles take


in electricity into the batteries which store energy in direct current (DC). Electricity is then fed into a DC/AC inverter where it is converted to alternating current (AC) electricity. This AC electricity is connected to a 3-phase AC motor to drive the wheels. It is notable that DC motors are also often used. Several electric cars now have a regen feature, such that during braking, the motor turns into a generator and delivers power back to the batteries. In recent production vehicles,


various motor types have been implemented: Induction motors within Tesla cars and permanent magnet machines in the Nissan Leaf and


of converting the electrical energy to mechanical energy. Approximately 75% - 90% of the energy from the battery is converted to mechanical energy, the losses being in the motor and drivetrain. In February 2024, there were over


one million fully electric vehicles and a further 600,000 thousand plug-in hybrid vehicles in the UK. This is a significant rise from just under 300,000 combined full electric and plug-in hybrids in 2019.


How do we control motors? Different starting methods are employed for starting induction motors because the motor draws more current during starting in order to overcome its initial inertia; also, to prevent damage to the windings due to the high starting current flow. The simplest form of motor


starter for the induction motor is the Direct On Line (DOL) starter which essentially connects the motor direct to the supply. It is viable for scenarios where the load driven by the motor can cope with shock produced by the high starting torque. This control method is often used to start small water pumps, compressors, fans and conveyor belts. Star-delta or soft starters connect


the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps. With this form of starter, the three-phase supply voltage to the stator windings can be switched between star and delta configurations. Variable-speed drives (VSD)


present a most energy efficient method to control motors. VSDs provide a means of driving and adjusting the operating speed of a mechanical load. They are also known as variable frequency drives (VFD), however a VFD refers to AC drives


20


EIBI | MARCH 2024


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