Voltage Stability Investigation of Grid Connected Wind Farm Abstract—At present, it is very common to find renewable energy resources, especially wind power, connected to distribution systems. The impact of this wind power on voltage distribution levels has been addressed in the literature. The majority of this works deals with the determination of the maximum active and reactive power that is possible to be connected on a system load bus, until the voltage at that bus reaches the voltage collapse point. It is done by the traditional methods of PV curves reported in many references. Theoretical expression of maximum power limited by voltage stability transfer through a grid is formulated using an exact representation of distribution line with ABCD parameters. The expression is used to plot PV curves at various power factors of a radial system. Limited values of reactive power can be obtained. This paper presents a method to study the relationship between the active power and voltage (PV) at the load bus to identify the voltage stability limit. It is a foundation to build a permitted working operation region in complying with the voltage stability limit at the point of common coupling (PCC) connected wind farm. Keywords—Wind generator, Voltage stability, grid connected I. INTRODUCTION. ECENTLY Wind Generator (WG) has been experiencing a rapid development in a global scale. The size of wind turbines and wind farms are increasing quickly; a large amount of wind power is integrated into the power system. As the wind power penetration into the grid increases quickly, the influence of wind turbines (WT) on the power quality and voltage stability is becoming more and more important.. Highlight a section that you want to designate with a certain style, then select the appropriate name on the style menu. The style will adjust your fonts and line spacing. It is well known that a huge penetration of wind energy in a power system may cause important problems due to the random nature of the wind and the characteristics of the wind generators. In large wind farms connected to the transmission network the main technical constraint to take into account is the power system transient stability that could be lost when, for example, a voltage dip causes the switch off of a large number of WGs. In the case of smaller installations connected to weak electric grids, power quality problems may became a serious concern because of the proximity of the generators to the loads. Trinh Trong Chuong is with the Department: Electric Power System, Hanoi University of Industry, Vietnam. Email: chuonghtd@gmail.com. Tel: (+84)0904993611 The existence of voltage dips is one of the main disturbances related to power quality in distribution networks. In developed countries, it is known that from 75% up to 95% of the industrial sector claims to the electric distribution companies are related to problems originated by this disturbance type [4, 5]. These problems arise from the fact that many electrical loads are not designed to maintain their normal use behaviour during a voltage dip. The aim of this paper is to conduct a voltage stability analysis using exact representation of distribution line with ABCD parameters, to evaluate the impact of strategically placed wind generators on distribution systems with respect to the critical voltage variations and collapse margins. This paper concludes with the discussion of wind generators excellent options for voltage stability [1]. II. INDUCTION MACHINES Induction machines are use extensively in the power system as induction motors but are not widely used as generators. Despite their simplicity in construction, they are not preferred as much as synchronous generators. This is mainly due to the defined relationship between the export of P and absorption of Q. However, induction generators have the benefits of providing large damping torque in the prime mover, which makes it suitable for the application in fixed speed WTs. The fixed speed WT uses a squirrel cage induction generator that is coupled to the power system through a connecting transformer as shown in Fig 1 [1]. Due to different operating speeds of the WT rotor and generator, a gearbox is used to match these speeds. The generator slip slightly varies with the amount of generated power and is therefore not entirely constant [4]. Fig. 1 Modelling wind turbine connected grid [1] However, because these speed variations are in the order of 1 per cent this wind turbine is normally referred to as constant speed. Nowadays, this type of wind turbine is nearly always combined with stall control of the aerodynamic power, although pitch-controlled constant speed wind turbine types have been built in the past. Induction machines consume reactive power and consequently, it is present practice to provide power factor correction capacitors at each WT. These are typically rated at around 30 percent of the wind farmcapacity. As the stator voltage of most wind turbine electrical generators is 690V, the connecting transformer of Trinh Trong Chuong R gearbox G vG PG QG Wind turbine Grid iG Induction Generator World Academy of Science, Engineering and Technology International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering Vol:2, No:6, 2008 1163 International Scholarly and Scientific Research & Innovation 2(6) 2008 scholar.waset.org/1999.5/14898 International Science Index, Electrical and Computer Engineering Vol:2, No:6, 2008 waset.org/Publication/14898