Title page for etd-0204104-103739


[Back to Results | New Search]

URN etd-0204104-103739
Author Jong-ian Tsai
Author's Email Address No Public.
Statistics This thesis had been viewed 4711 times. Download 3788 times.
Department Electrical Engineering
Year 2003
Semester 1
Degree Ph.D.
Type of Document
Language zh-TW.Big5 Chinese
Title Torsional Torques and Fatigue Life Expenditure for Large-Scale Steam Turbine-Generator Shafts and Blades Due to Power System Harmonics
Date of Defense 2004-01-30
Page Count 156
Keyword
  • Turbine
  • Blade
  • Electrical Arc Furnace
  • High Voltage DC Transmission
  • Harmonics
  • Fatigue Life Expenditure
  • Torque Vibration
  • Shaft
  • Abstract During the three decades, the torsional impact on turbine-generator sets due to power system disturbances has been extensively discussed in many research works. However, most of them are focused on the fatigue damage of turbine shafts due to large-signal disturbances. For example, network faults occur. Obviously, the torsional effect subject to small-signal disturbances has not received much attention. In fact, although the small disturbances would not immediately damage the turbine mechanism, the cumulative long-term damaging effects may not be negligible under certain circumstances.
    Many operating conditions in power systems may lead to small disturbances on blades; for examples, shedding loads, switching transmission line, resetting control system parameters, and harmonics etc. Nevertheless, others only cause short-term or transient non-resonant disturbances occasionally except the power system subharmonics which could results in electro-mechanical resonance. Therefore, two types of subharmonics in power systems are proposed so as to investigate the toque impact and long-term fatigue life expenditure in turbine shafts and blades.
    Firstly, from the steady-state disturbance viewpoint, the long-term cumulative fatigue estimation based on the three-year project of the GE Co. shows that there are potential damages for both the shafts and the blades of the nearby generators caused by the subharmonic excitations of the HVDC link. The fatigue life sensitivity works are also carried out to provide the recommendations for the safety operation. The optimal damper type and disposition scheme for depressing the resonant torque and prolonging the turbine lifetime is consequently motivated, which is based on participation factor of linear systems with the electromechanical analogy. The effectiveness of this scheme on suppressing vibration torque arising from network faults is also satisfying. In addition, the authors propose the new electromechanical supersynchronous resonance phenomenon for the turbine-generators near the inverter station owing to asymmetric line faults near the rectifier station.
    Secondly, the dramatic real and reactive power consumption during the melting period of an electrical arc furnace load. The voltage flicker pollution is mainly caused by the reactive power fluctuation while the stochastic subsynchronous oscillation in turbine mechanism is excited by the electromagnetic torque of the subsynchronous frequency which is induced by the real power fluctuation. Such a small stress imposed on the low-pressure long turbine blade combined with its evitable corrosive environment contributing to the corrosion fatigue effect. Although the voltage flicker severity at the point of common coupling is still within the limit, the blade may have been damaged from the long-term corrosion fatigue life expenditure estimation. In other words, the conventional voltage flicker limit established to make human-eye comfortable might not protect the blade from damaging risk. The long-term influence resulted from the electric arc furnace loads cannot always be neglected. It is necessary to take care of the blade material intensity and operating environment. If there is the potential of blade damage, one has to strengthen the output capacity at the power plant or separate the peak load durations among the steel plants to limit the over-fluctuation real power of the generator.
    Advisory Committee
  • Yin-Chyn Wu - chair
  • Gary-W. Chang - co-chair
  • Whei-Min Lin - co-chair
  • Chwen Chyn - co-chair
  • Jiann-Fuh Chen - co-chair
  • Ta-Peng Tsao - advisor
  • Files
  • etd-0204104-103739.pdf
  • indicate accessible in a year
    Date of Submission 2004-02-04

    [Back to Results | New Search]


    Browse | Search All Available ETDs

    If you have more questions or technical problems, please contact eThesys