Motor energy use, efficiency and loading
How electric motors work and the energy savings that can be made during start-up and by correct loading.
By understanding how an electric motor works you can get a better idea of how energy wastage in your business may occur.
Reducing wear when starting an electric motor
A motor connected directly to an electrical power supply accelerates to a fixed speed. When it starts up, the motor draws a very high current as it accelerates - this is known as the 'motor starting current' and it generates a great deal of heat. This excess heat considerably increases motor wear and reduces its life expectancy. For this reason, motor manufacturers normally give a maximum number of 'starts' per hour.
However, by connecting a motor to a 'soft starter' or a variable-speed drive (VSD) the starting current can be limited. This gives a much smoother start and results in less wear on the motor. To find out more about soft starters and VSDs, see upgrading your system equipment.
Electric motor loading
Only around 75 to 80 per cent of the energy put into an electric motor is used by the load being moved. This includes:
- heat wastage of around five per cent in the motor's drive unit
- internal losses in the motor of around eight per cent
- additional losses through friction if the motor is attached to a transmission system like a gearbox or pulley
The 'loading' of a motor is the actual amount of work it does compared with its maximum rated power output. For example, a motor rated at 90 kilowatts driving an 81 kilowatt load is described as 90 per cent loaded. Modern motors typically operate most efficiently at above 75 per cent loading, peaking at around 90 per cent efficiency.