The Finland-based company The Switch is a world leader in directly driven permanent magnet generators (PMG) for wind turbines with a power output of 1 MW up to 5 MW at medium to high rotational speeds. To determine the efficiency of the generators, a torque flange from HBM is installed into the shaft train as additional measuring system.
Combined with special converters and monitoring and control systems the solutions offered by the company can be integrated into the drive train of wind turbines as complete packages. The PMGs offered by The Switch feature a special, patented arrangement of the permanent magnets. This arrangement enables both high efficiency and a smooth running of the turbine. Use of a direct drive eliminates the need for a transmission gearing and results in reduced mechanical stress on the system as well as increased reliability and a longer service life.
The technical challenge is to control high torque and, at the same time, achieve high efficiency. To determine the efficiency, two identical generators are installed such that their shafts can be directly connected for testing. The generator under test is driven by the second generator which, in this case, functions as an engine. Current and voltage measurements on both generators enable a relationship between the power output and the power consumption to be established and thus to determine the efficiency.
The Switch installs a torque flange into the shaft train as an additional measuring system. A resulting benefit is the verification of the efficiency determined through measurement of the electrical parameters. Moreover, effects resulting from modifications to the engine or generator or from simulation of different loading scenarios can be determined fast and precisely. However, the main parameter for determining the efficiency is the transmitted power. Through direct measurement of torque and rotational speed of in the shaft train transmitted power, measurement uncertainty is small.