Title: Process optimisation by using variable speed drives.
Author: Dr. Sven Demmig / Siemens AG of Germany / Drive Technologies
Abstract: At the beginning of the industrialization one electrical motor was driving multiple machines. This has been succeeded by one motor for each machine. The speed could only be adjusted by the number of pole pairs. The process had to be optimized if possible by mechanical components. Since variable speed drives are available the process can be optimized directly by controlling the speed and the torque of the motors. Due to the progress in the development of electrical motors direct integration of the motor in the mechanical train is possible. Additional, new drive technologies offer higher dynamics, higher power and improved control possibilities. New topologies reduce the impact of the drive at the motor and the line side. Process specific control algorithms are implemented directly within the drives. Furthermore the sensors of the drive system are used for monitoring the status of the process and the conditions of the different drive train components. This offers the possibility of planning preventive maintenance and monitoring the drive e.g. via the Internet.
Because of the wide range of available drives and motors for different applications the best drive system solution can be found. Following a few examples are shown. In order to increase the efficiency of high power LNG trains the gas turbine has been replaced by electrical drive systems on some projects. This was only possible because of the availability of drive systems up to 120 MW. More and more Electrical Submersible Pumps are fed by a drive in order to run at optimum speed. Necessary for this application are drives that are able to feed a motor over a long cable connection in the range of a few kilometers. In order to reduce the size of the equipment and to omit the gear box there is a trend to integrate the motor directly in the machine. One example is a cement mill having an integrated permanent magnet motor that has just been developed.
On the one hand drive systems are available for new applications with optimized processes. On the other hand more and more solutions are on the market for retrofitting existing applications in order to optimize the process and reduce energy consumption. Drives have been introduced that are able to run with existing direct on line motors. Complete drive systems have been developed that meet the space requirements of existing machines.
The progress in drive technologies and motors offers a lot of new possibilities in order to optimize the process of new and existing plants. By using variable speed drives the process can be optimized regarding quality, availability and the power consumption, just to mention some examples.