Impact of Wind Generation Mix on Transient Stability for an Interconnected Power System Lasantha Meegahapola 1 , Damian Flynn 2 , Jason Kennedy 3 and Tim Littler 4 Power & Energy Research Centre, The Queen’s University of Belfast, United Kingdom 1 lmeegahapola01@qub.ac.uk, 2 d.flynn@qub.ac.uk, 3 jason.kennedy@qub.ac.uk, and 4 t.littler@qub.ac.uk Abstract The rapid growth of wind generation in many European countries is pushing power systems into uncharted territory. As additional wind generators are installed, the changing generation mix may impact on power system stability. This paper adopts the New England 39 bus system as a test system for transient stability analysis. Thermal generator models are based on a likely future plant mix for existing systems, while varying capacities of fixed-speed induction generators (FSIG) and doubly-fed induction generators (DFIG) are considered. The main emphasis here has been placed on the impact of wind technology mix on inter-area oscillations following transient grid disturbances. In addition, both rotor angle stability and transient voltage stability are examined, and results are compared with current grid code requirements and standards. Results have shown that FSIGs can reduce tie-line oscillations and improve damping following a transient disturbance, but they also cause voltage stability and rotor angle stability problems at high wind penetrations. In contrast, DFIGs can improve both voltage and rotor angle stability, but their power output noticeably oscillates during disturbances. Keywords: DFIG, FSIG, inertial response, inter-area oscillations, rotor angle stability, voltage stability 1. Introduction Rapid developments in distributed generation, system interconnection and synchronous islanding have given rise to new issues for power system planning and operation. In this context, power system transient stability is a major concern for both academia and industry. Wind generation, in particular, has become the most dominant form of distributed generation in many European countries [1-2]. The island of Ireland, for example, is likely to install 5500 MW wind power, which will constitute 40% by 2020 [3]. It is anticipated that this capacity will largely employ DFIG-based wind farms. Modern power networks are increasingly interconnected by tie-lines with more generation coming from distributed generation, consequently raising system security concerns in terms of transient stability. A number of studies have been conducted on the highly interconnected European power network [4-5] to investigate inter-area oscillations in different parts of the network. They have adopted methods based on eigenvalue analysis and the fast Fourier transformation (FFT). These studies have investigated the inter-area oscillations from a small signal stability perspective. They have analysed power flow oscillations in tie-lines, frequency oscillations in each part of the interconnected system and concluded that sufficient damping can be achieved through extra control measures taken at conventional power plants, such as power system stabilisers. The Irish power system is comprised of networks in Northern Ireland and the Republic of Ireland, which are mainly interconnected by a 275 kV double-circuit transmission line. Tie- line oscillations in this interconnector have also been analysed and it has been concluded that certain oscillatory modes are correlated with power variations from wind farms [6]. A study conducted on wind power integration for the Nordic power network [7] analysed the damping effect on inter-area oscillations with different wind generator technologies. A further grid study conducted on large-scale wind power integration has also analysed the effect on inter-area oscillation damping with different generators [8]. Both studies have investigated the effect of wind generator technology on inter-area oscillations based on small signal stability. They have concluded that FSIGs can damp inter-area mode oscillations while DFIGs decrease the damping. Studies conducted from a transient stability perspective are less common in the literature. In addition, wind