Reliable Protective Scheme for Integrating Variable Capacity Micro Grids Using Superconducting Fault Current Limiters

Abstract

Dispersed generations (DGs) have its vital importance in the increasing power demand scenario. The penetration of the new generating facilities like wind, solar power etc has serious effects on the stability and the reliability of the power system. As this penetration increases, there will be a corresponding increase in the fault current level of the system which could result in fault current over duty burden. Existing power system equipments like circuit breaker capabilities and protective relay settings which are already designed for a system without considering the DGs, will not have the required ratings to withstand this severe condition. Thus, the most important challenge is their reliable integration with the Main Grid. To overcome this problem, there is a need for protection system redesign or a complete system up-gradation, which could be very expensive. The use of Fault Current Limiters (FCLs) is one of the most economical and effective solutions for the above said problem. This paper discusses the use of Superconducting Fault Current Limiters (SFCLs) as a Unidirectional Fault Current Limiter (UFCL). SFCLs are the ‘invisible elements’ in the power system under normal operation and is visible only when a fault occurs. Through this paper, reliable integration schemes for the Variable Capacity Micro Grids (VCMGs)/Renewable Energy Generation (REG) using USFCL is introduced. Simulation studies were conducted using PSCAD and numerical analyses were done to explain the effectiveness of the proposed protective system. Also, a PSCAD model of USFCL for unsymmetrical fault analysis is proposed. The proposed integration schemes prove to be reliable as it ensures an improved power quality of the micro grid and retains the protective co-ordination of the relays, thus, helping in the use of the existing protective system effectively when the VCMGs/REG are installed in the power system.