Implementation of Resistive Type Superconducting Fault Current Limiters in Electrical Grids: Performance Analysis and Measuring of Optimal Locations

In the past few years there has been a significant rise in the short-circuit current levels in transmission and distribution networks, it due to the increasing demands on power and the addition of sources of distributed generations. It leads to the need of integration of novel protection systems such as the superconducting fault current limiters (SFCLs), as the installation of these devices into the electric network aims to improve the overall system stability during normal and fault conditions, whilst the upgrading costs associated to the increasing demand for integration of renewables to the power grid are minimized. SFCL models on the electric distribution networks largely rely on the insertion of a step or exponential resistance that is determined by a predefined quenching time. However, beyond the framework of these models, the study of the performance, reliability, and location strategy for the installation of sole or multiple SFCLs in power grids still lacks of proper development leading to the utter need of comprehensive and systematic studies on this issue. In this paper, we expand the scope of the aforementioned models by considering the actual behaviour of a SFCL in terms of the temperature dynamic power-law dependence between the electrical field and the current density. Our results are compared with step-resistance models for the sake of discussion and clarity of the conclusions. Both SFCL models were integrated into a power system model built based on the UK power standard, and the impact of these protection strategies on the performance of the overall electricity network was studied. As a representative renewable energy source, a 90 MVA wind farm was considered for the simulations. Three fault conditions have been simulated, and the figures for the fault current reduction predicted by both fault current limiting models have been compared in terms of multiple current measuring points and allocation strategies. Consequently, we have shown that the incorporation of the E−J characteristics and thermal properties of the superconductor at the simulation level of electric power systems, is crucial for reliability estimations and optimal location of resistive type SFCLs in distributed power networks. Our results may help to the decision making by the distribution network operators about investment and promotion of the SFCL technologies, as a maximum number of SFCLs for different fault conditions and multiple locations has been determined. Manuscript Submitted June 19, 2015. X. Zhang, Z. Zhong, and T. A. Coombs are with the Electronics, Power and Energy Conversion Group, Department of Engineering, Electrical Engineering Division, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, U.K. (e-mail: [email protected]) H. S. Ruiz is with the Department of Engineering, University of Leicester, Leicester LE1 7RH, U.K., and also with the Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, U.K. (e-mail: [email protected]). This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) project NMZF/064. X. Zhang acknowledges a grant from the China Scholarship Council (No. 201408060080).