The BL-MOTOR drive system (BL = brushless ) mainly comprises a simple thyristor converter and synchronous machine, which is excited by brushless means. Nowadays, the applications normally feature large driving power, e.g. greater than 3MW. In those cases, it is not possible to feed asynchronous squirrel cage motors with converter on technical or price grounds. The reference lists pertaining to BL motors shows the following applications over the past 15 years: piston compressors, turbo compressors, extruders, mixers, ship propulsion, pumps, ventilator. The BL-converters comprise a control-regulation-excitation cabinet and one or more thyristor cabinets. For the latter, standard power components with air cooling, air-water cooling or pure water cooling are used. The driving power is practically unrestricted, 50MW and more being possible. 6-, 12- and 24-pulse circuits have been designed. The efficiency amounts to approx. 99.0 %, 4-Q operation being standard. Any nominal driving speed can be selected. 2 examples:

• 20MW 135 rpm motor for ship propulsion: 16-pole converter, frequency 0- 18Hz
• 5MW 6000 rpm motor for feed pump: 2-pole converter, frequency 0-100Hz