Electrical energy savings in excess of 40% are achievable, by improving energy efficiency in drive systems is the statement made by CEMEP, the European Committee of Manufacturers of Electrical Machines and Power Electronics.  CEMEP has updated its 32-page guidance brochure of the same name, which is available from the Gambica website.

The brochure shows the potential offered by choosing the correct drive system to save energy, how the normative and legislative environment is defined on the national and international markets, and finally considers future developments.

The potential energy savings from electrical drive systems are approximately 40 per cent, through overall system optimisation (10 per cent from increased use of energy-efficient motors, 30 per cent from electronic speed control). Their essential components (switchgear or variable speed drive, electric motor and gear unit) therefore deserve particular attention.

About 60 per cent of total potential energy savings can be achieved by mechanical system optimisation of the machine itself (optimising pump impeller, fan blade angles etc.). The brochure concentrates on the other potential savings that can be achieved by the design of the electrical drive systems. These are quite substantial as well, amounting to 40 per cent of the total potential.

Consider the entire drive train

Electric drive systems essentially consist of the following components:

• a device for controlling the motors from the power grid, usually a contactor, soft-starter or variable speed drive;

• an electric motor that converts electrical power into mechanical power;

• a gearbox that adjusts the motor’s mechanical speed to the working point of the driven machine.

Some fixed-speed applications do not need a variable speed drive, merely a contactor for switching the motor on and off, or a soft-starter for soft motor start-up. In other applications, such as pumps, the speed of the electric motor is matched to the speed requirement of the machine, so that the gearbox is not required.

Variable speed drives

For speed control of a three-phase motor, the frequency and the voltage have to be varied. This is automatically done in a variable speed drive (sometimes called an inverter drive). A wide power range of variable speed drives is available, from a few watts to several megawatts.

Over the past few decades, their properties (start-up, power losses, size, cost) have been continually improved by the progress made in microelectronics and in power electronics. The performance of a controlled three phase motor meets today’s highest requirements. The efficiency of modern-day variable speed drives typically lies between 96 and 98 per cent (depending on power) and is determined by the efficiency of the power electronics.

The principal task of a variable speed drive is to control the motor’s speed. According to the requirements of the process, the motor’s speed can be changed to match the process need and thus optimize the energy taken from the grid.

This mode of process control offers enormous potentials in terms of energy savings, and is significantly more efficient than a throttle control, for example, in a pump application. EU’s Motor Regulation also permits the use of an IE2 motor with speed control using a variable speed drive as an alternative to a line-operated IE3 motor.

CEMEC guide from Gambica

More energy saving inverter drives here