Industry

Electrical Drives

Trade and industry require electrical drives worldwide. Motor-driven systems consume 64% of all electricity used in industry. Here, there is also great potential for improved efficiencies.

Picture: BMWi

Electrical drive systems consist of the following units:
The electric motor, which converts electric power into mechanical power, A frequency converter, which converts the electrical power of the mains in a controlled form (electronic speed control), And the gearbox, which adjusts the mechanical power of the motor to the working point of the driven machine (reducing speed and increasing torque). The individual components have been highly optimised already. However, there remains an enormous savings potential in the use of optimum system concepts if such concepts are evaluated by their costs across the entire life cycle. When you consider the lifetime of an electric motor, the costs associated with the consumption of electricity account for up to 96% of the total cost. Therefore, when purchasing a motor, it is important to bear in mind its expected electricity consumption as this is a considerably greater factor than the initial purchase cost.

Great savings potential in electrical drive systems lies in the use of energy-saving motors. These energyoptimised motors convert electrical into mechanical energy with the fewest possible losses whilst maintaining the required technical properties. In industry, three-phase asynchronous motors are widely used as standard drives. They are good value for money and reliable machines that require very little maintenance. In terms of energy efficiency, strong efforts have been made in the past years to reduce the energy losses of such asynchronous machines substantially.

In the highest class of the European motor efficiency scale, EFF 1, losses are on average reduced by 40%. Higher efficiency levels may be obtained when using special motor types such as synchronous motors or EC motors:

• Synchronous motors have a very high electrical efficiency, even during partial load operation. Precise regulation of frequency converters is possible
• Electronically commutated (EC) motors, also known as brushless DC motors (BLDCs), supplement the positive attributes of synchronous machines by being able to adjust to their load. They are highly efficient, even when working with partial loads, have a high power spectrum and are easily regulated.

In 1998, the European motor manufacturers made a voluntary agreement towards the European Commission to promote selling energy-saving motors. The share of energy-saving motors of efficiency class EFF 1 has been rising constantly ever since. Simply replacing an old motor with an EFF 1 motor is, at first glance, the simplest step toward achieving energy efficiency. To assess, however, the economic efficiency of an electrical drive, it is not primarily the motor that determines the optimal efficiency but rather the way in which the motor or machine speed is controlled. The savings potential of electronic speed control is four to five times greater than that of highefficiency motors. Electronic speed control can save between 20% and 70% of the energy costs of conventional mechanical methods such as throttle valves or flaps.

Taking life cycle costs into consideration, investments made in energy-saving methods can often be redeemed within a matter of only a few months. Only about 12% of the motor capacity installed in Germany today is operated with energy-saving electronic speed controls. It is  estimated, however, that it would be beneficial for over 50% of this motor capacity to be equipped with electronic speed control.

There are basically two different types of industrial drive systems:

• Drive systems, which require an electronic speed control simply for them to work.
  Electrical drives that could be operated, in principle, without speed control. They run continuously at fullpower independent of the varying load requirements of the machine. It is in this group that the use of electronic speed controls opens up great energy savings potential.
• The great energy savings potential that lies in mechanical system optimization falls within the competence of mechanical engineers and designers of machinery and plants. It accounts for almost 60% of total energy savings potential in electric motor driven systems.

In drive engineering, there are numerous ways to save energy and increase efficiency:

•  Use motors that have the best possible efficiency class, for example, the "CEMEP seal of approval" (CEMEP: European Committee of Manufacturers of Electrical Machines and Power Electronics).
• Use motors that have variable power.
• Use frequency converters (recuperation of brake energy into the system). 

Several projects are currently underway in a bid to unlock more potential energy savings in trade and industry. One such project, in particular, is the "Motor Challenge Programme". Its goal is to motivate companies to optimise the efficiency of their electric motor systems. For decades, electrical drive engineering has been one of the German economy?s main export items. Both a proclivity for innovation and comparatively high energy costs in Germany contribute to Germany?s high-tech products receiving increasing levels of global attention because of their impressive energy efficiency.