Abstract
This paper presents a simple analysis tool for torsional vibration of the rotor shaft of turbine generator which is interconnected with a power system with self-commutated converters. The evaluation is based on the analysis of measurement data in the field and the instantaneous value based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originated from self-commutated converters cause the torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machine and converters is known as sub-synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft cause the large torsional vibration, which leads to the shaft damage. In this paper, the influence of interharmonics to turbine generators is investigated. If there were air gap torque fluctuations with frequency near the natural frequency caused by interharmonics, which have frequency less than 100 Hz of sideband wave caused by asynchronous pulse width modulation, the rotor shaft might be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact to the generator are investigated.
