CIRED Workshop - Rome, 11-12 June 2014 Paper 0362 Paper No 0362 Page 1 / 5 USING REACTIVE POWER FROM WIND TURBINES FOR LOSS REDUCTION IN DISTRIBUTION SYSTEM Shemsedin SALIH Chalmers University of Technology – Sweden Shemsedin.nursebo@chalmers.se Peiyuan CHEN Chalmers University of Technology – Sweden Peiyuan@chalmers.se Ola CARLSON Chalmers University of Technology – Sweden Ola.carlson@chalmers.se ABSTRACT Considering the majority of the power losses occur in distribution systems, it is worthwhile to investigate the use of reactive power compensation (RPC) from wind turbines installed in the distribution system for loss reduction. Therefore, this paper analyses the effectiveness of the RPC for loss reduction under different system conditions. These include power factor of the system load, X/R ratio of the cables, and the electrical location of the wind turbines. The result of the analysis shows that the effectiveness of RPC for loss minimization mainly depends on the power factor of the load followed by the location of the wind turbine in the system. In this regard, in a system where the average load power factor is around unity, e.g. 0.98, RPC is not attractive for loss reduction. However, when the average power factor of the load is around 0.90, RPC is able to decrease the system loss by around 20%. Though the 2/3 rule can be applied to site wind turbine for maximum loss reduction through the use of RPC, the overall sitting problem of the wind turbine is more likely to be dependent on its active power output rather than RPC. The X/R ratio of the cable, on the other hand, has very little impact on the effectiveness of the approach. INTRODUCTION The ongoing increase in the introduction of wind power into the distribution system has presented distribution network operators (DNOs) with a number of challenges and opportunities. The challenges relate to the effect of wind power on the power quality and reliability of the system. These effects are widely investigated [1], [2] and mitigation solutions are also proposed to increase the wind power hosting capacity of distribution systems [3], [4]. On the opportunities side one can mention the possible decrease in system power loses. However it is widely known that wind power, distributed generation (DG), in general, can decrease the power losses in a given distribution system depending on its capacity and location in the distribution system [5], [6]. Thus, the sizing and sitting of DG to achieve maximum loss reduction has been the subject of numerous papers [6]–[8]. Beside the loss reduction through the provision of active power locally, wind turbines present the DNO with flexible reactive power to improve the voltage profile of the system and to reduce the system loss. In this regard, considerable research efforts have been devoted to deal with optimizing reactive power output of a wind power plant to minimize the power losses and improve the voltage profile of the system [5], [9], [10]. These papers, however, are interested in either with optimization approach or the algorithm of the optimization model. In contrast, this paper analyzes under what power system conditions reactive power compensation (RPC) can be an attractive solution for loss reduction. LOSS REDUCTION USING REACIVE POWER COMPENSATION IN A DISTRIBUTION SYSTEM RPC in a distribution system can contributes to power losses reduction by providing the reactive power demand in the system locally, which would have been supplied from the external grid through the substation transformer. This will reduce the current flow through the cables in the system, and reduce the system power losses. This section investigates the impact of the following three parameters of the system on the effectiveness of RPC for loss reduction:  Power factor of the loads in the system  X/R ratio of the cables connecting the reactive power source (RPS) to the substation  The location of the RPS in the feeder The size of the RPS is also an important factor. However, since the sizing of the RPS depends on the power factor of the load and the location of the RPS, it is not investigated as a separate factor. To carry out the investigation, the simple radial distribution system shown in Fig. 1 is used. Main grid Z 1 Z 2 Z 3 P 1 ,Q 1 P 2 ,Q 2 Reactive power source (RPS) 1 2 3 4 Figure 1 A simple radial feeder For each combination of power factor of the load, X/R of the cable, and location of the RPS, the optimal level of reactive power injection and the resulting decrease in power losses is calculated using an optimal power flow program. It is assumed that the loads in the system are of constant power type. The maximum feeder load is chosen to be 3.7 MVA. The total impedance of the cable   3 2 1 Z Z Z Z tot    is chosen to be 1.5 Ω so as to make sure that the voltage at the end of the feeder