# Impacts of Integration of Wind Farms on Power System Transient Stability
## 1 Introduction  
With the growing population, the electrical load is increasing day by day. To compensate the ever-growing energy gap, renewable resources have undergone fast expansion worldwide in recent years [1], but they also result in some challenges for power system operation such as the static security and transient stability issues [2; 3]. In particular, as wind power generation accounts for large share of these renewable energy and reduces the inertia of the power network, the transient stability of power systems with high-level wind generation is decreased and has attracted wide attention recently [4; 5]. Therefore, it is of great significance to effectively evaluate the influence of wind power generation on power transient stability to improve the safe level of power system operation. In practice, a power system is widely disturbed by small and large disturbances. Since small disturbance is constantly occurring in the form of load changes, the system must be able to accommodate these fast changing conditions and ensure satisfactory operation [6; 7]. However,the more important thing is that the system should survive serious disturbances such as the loss of large generators or transmission line faults or short circuits, which is the so-called transient stability problem. Transient stability is the capability of a power system to regain a stable equilibrium operation point when exposed to a severe disturbance, where the dynamic behaviours and interactions of multiple complex dynamic components should be considered [8; 9]. If the power system is stable after large disturbance, it will get to new state of balance for maintaining the integrity of the system. Some loads and generators may be isolated from fault components or intentionally tripped to maintain operation continuity of most systems. Interrelated systems can also be intentionally divided into two or more islands for some serious disturbances. The operation of an automatic control device and the system operators eventually restore the system to a normal state. If the system is in the state of instability, it will cause run-down or run-away states [9; 10]. For example under a sustained fault, the angle separation of the generator rotor increases gradually, or the bus voltage gradually decreases. Unstable system conditions may lead to cascading outages and turn off the main part of the power system. It is very important to conduct stability analysis when the system is connected to a renewable energy system like wind farms, to avoid system instability [11; 12]. There are numerous types of wind turbines in which a doubly fed induction generator (DFIG) has become an advanced development and the mainstream technology because of the high energy efficiency, low power consumption of the electronic converter and the low mechanical stress of the wind turbine [13]. The dynamic response of DFIG depends mainly on the well-coordinated control strategy of the converters in the DFIG excitation system, which is basically different from the old synchronous generator. With the continuous increase in penetration of wind power, it has become an important issue to systematically and effectively evaluate the impact of integrated DFIGs on transient stability [14]. The influence of DFIG integration on power system transient stability has received considerable attention, and the influence of integrated DFIGs on rotor dynamics of synchronous generator can be studied. Some important work about the different network structures, different penetrations of DFIG, and common coupling points to evaluate the impacts of integrated DFIGs was investigated in [15]. To find the equivalent inertia of all power sources, i.e., generators or wind turbines, the use of synchronous pharos measurement can found in [16]. Authors of [17] explored the relationship between wind power generation and the rotor angle stability of conventional synchronous generators from the viewpoint of controlling the reactive power from variable speed wind turbine generators in the system.