Analysis of Active SFCL by Design of Control Strategies for Fault Detection and PWM Converter and Protection Coordination with Distance Relay

In this paper, the influence on the voltage compensation type, active superconducting fault current limiter (ASFCL) is investigated under symmetrical and asymmetrical fault conditions. ASFCL is consisting of three air-core superconducting transformers and a three-phase voltage source converter. In the normal (no fault) state, the flux in air core is compensated to zero, so the ASFCL has no influence on the main circuit. In the case of short circuit, by controlling the amplitude and phase angle of the second winding’s current, the limiting impedance which is in series with the AC main circuit can be regulated, and the fault current will be limited to a certain level. Control strategies consist of fault detection and PWM converter operation is designed. To simplify the design of controllers the mathematical equations can be expressed in synchronous rotating d-q frame. Furthermore, under the condition that the active SFCL is placed behind the relay element, its current-limiting impedance will be added into the measured impedance between the relay and the fault points. As a result, in order to prevent the refused operation of the relay, According to the two different operation modes of the active SFCL, in this paper present the corresponding two modified formulas. Using MATLAB SIMULINK, model of the three phase AC system with ASFCL is created and control strategies test, fault current limiting test, and distance relay operation is investigated.