Torsional stability of hydropower units under influence of subsynchronous oscillations

• Hydropower units are known to be comparatively insensitive to subsynchronous power oscillations. During a startup test of an electrical island in the Nordic power system, a series capacitor tripped due to a subsynchronous oscillation within the normal frequency range of hydropower unit torsional modes. Since no thermal units were connected, it is motivated to question the traditional view. In this paper, the small-signal and transient torsional mode stability of hydropower units is assessed through time-domain simulations. The model is based on the first IEEE benchmark model for subsynchronous resonance which has been tuned to fit one of the blackstart test system units for which detailed measurements are available. The stability conditions are investigated for several load conditions and machine configurations. It is found that the damping in the startup test system is sufficient to prevent growing oscillations. A fault however could expose the machines to high transient torques.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

Teknisk fysik med inriktning mot elektricitetslära

Engineering Science with specialization in Science of Electricity

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