Negnevitsky, "Subsynchronous torsional interaction behaviour of wind turbine-generator unit connected to an HVDC system," in IECON 2010: 36th Abstract-Utilisation of wind energy to generate electricity has attracted considerable attention worldwide, and is rapidlygrowing. The integration of large wind farms with high voltage direct current (HVDC) transmission network could be one of the preferred options for supplying bulk power over a long distance. Since HVDC rectifier stations with constant current control may introduce negative damping on the nearby generating units, it is important to identify the torsional interaction characteristics between turbine-generator units and the HVDC systems over a frequency range of interest. However, very little related information exists in regard to wind turbine-generators. This paper presents the electromagnetic transient time domain analysis to investigate the possible subsynchronous torsional interaction (SSTI) phenomenon of fixed-speed (induction machine based) wind turbine-generator (WTG) unit interconnected to a CIGRE first HVDC benchmark system. Electrical disturbances, such as three-phase short circuit fault at the inverter station and DC power flow change are simulated to examine the possible dynamic interactions of the WTG unit. Simulation studies are conducted using PSCAD R /EMTDC c .

Power system performance is affected by dynamic characteristics of hydraulic governor-turbines during and following any disturbance, such as occurrence of a fault, loss of a transmission line or a rapid change of load. Accurate modelling of hydraulic governor-turbines is essential to characterise and diagnose the system response during an emergency. In this article, both detailed and simplified hydraulic systems governed by proportional-integral-derivative and proportionalintegral controllers are modelled. This article examines their transient responses to disturbances through simulation in Matlab/Simulink. The article also investigates the dynamic performance of an isolated hydraulic system through evaluating stability margins, eigenvalues, root loci and frequency deviation time responses of the system. The results obtained provide an insight into the stability of the power system governed by different governor settings.

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Classical ideal lossless representation of the hydraulic turbine has been used widely in the past for governor stability studies. This model is suitable for small perturbations around the initial operating condition, and approximates to the practical turbine characteristics at low frequencies only. For satisfactory fast response and stable operation of governor studies, this classical model may not be adequate, rather a more accurate modelling of the turbine-penstock characteristics is desired to capture and depict the essential dynamic performances for wide variety of system analyses. In this paper, a hydraulic turbine model with long penstock is represented where the water hammer effects and friction are taken in consideration. A detailed hydraulic turbine-penstock utilised for governing stability studies is used to analyse the transient response when subject to a load disturbance. Frequency response analysis as well as transient response analysis is performed to evaluate the effects of the detailed modelling of the turbine-penstock to the stability analyses and the dynamic performances. Index Terms--Governors, Hydraulic Systems, Hydraulic Turbine-Penstock Model, Stability VII. BIOGRAPHIESYin Chin Choo was born in Malaysia in 1983. She received her B.E. (Hons.) from the University of Tasmania, Australia, in 2005. She is currently pursuing the Ph.D. degree at the University of Tasmania. Her special fields of interests are power system analysis, hydroelectric turbines, power system stability and power system planning, operation and control.