# Dimensioning of Reactive Power Compensation in an Autonomous Island System
## 6 Conclusions  
This paper addresses the problem of appropriate dimensioning of the reactive compensation in the autonomous power system of Rhodes Island in Greece, which faces excessive reactive power system generation during low load periods, after major upgrades in its HV network. Against standard practice in interconnected power systems, in an autonomous system, the compensation level is not determined by local voltage management issues, but rather by the total reactive power absorption capability of voltage-regulating units, typically the synchronous generators in operation. This renders a cost-benefit analysis necessary for the problem, even though such an analysis is not typical when sizing reactive power compensation.  
A comprehensive method to determine the optimum size of reactive compensators is proposed, relying on a cost-benefit analysis approach that utilizes a detailed UC-ED model to suitably quantify system benefits due to the introduction of reactors. The proposed model complements the network analysis methods typically used for this purpose.  
The analysis performed in the paper indicates that the introduction of reactive power compensators in the network of Rhodes is justified from a system-level cost-benefit viewpoint. System cost estimation indicates that the introduction of 8 MVAr of reactive power compensation is optimal, while higher compensation levels (e.g., 12 MVAr) will also deliver substantial system benefits.  
Simulation of system operation with and without compensation showed that reactive power compensation will have a significant impact on mitigating renewable curtailments, which can be reduced from ~13% to ~8.5% when inductors in the order of 8 MVAr are installed. RES curtailment reduction constitutes an important criterion dictating the appropriate sizing of the required reactive compensation for the network of Rhodes Island,  
Figure 14: HV bus voltage (**a**) and frequency (**b**) at Soroni TPP—loss of S. Rhodes TPP.  
regardless of the system's economics, given the significance of exploiting available renewable resource towards power sector decarbonization.  
Finally, dynamic security assessment revealed that attempting to harvest the economic benefits of higher compensation levels (12 MVAr and beyond) can jeopardize system security in case of critical disturbances.  
Conceptualization, G.N.P., G.I.T. and S.A.P.; methodology, G.N.P., G.I.T. and S.A.P.; software, G.N.P. and G.I.T.; validation, G.N.P., G.I.T. and S.A.P.; formal analysis, G.N.P. and G.I.T.; investigation, G.N.P. and G.I.T.; resources, G.I.T. and S.A.P.; data curation, G.N.P. and G.I.T.; writing--original draft preparation, G.N.P. and G.I.T.; writing--review and editing, S.A.P.; visualization, G.N.P.; supervision, S.A.P.; project administration, G.N.P., G.I.T. and S.A.P.; funding acquisition, S.A.P. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by the Hellenic Electricity Distribution Network Operator (HEDNO) S.A.  
Not applicable.  
This work was supported by the Non-Interconnected Islands Department of the HEDNO S.A., who provided necessary data to perform the analysis. The authors would like to express their thanks to the management and the personnel of HEDNO S.A. for their support.  
The authors