The eventual goal of high-voltage direct-voltage (HVDC) systems is to implement HVDC grids. One of the key obstacles in realization of the HVDC grid is the absence of a dc circuit breaker (DCCB). Several prototypes of DCCBs for the HVDC grid have been proposed, but no commercial solution has been developed yet due to insufficient dc fault current breaking capabilities and an unreliable protection-coordination scheme. In this respect, application of the suitable fault current limiter is necessary, and the use of a superconducting fault current limiter (SFCL), which has already been developed for the ac grid, is a viable solution, but there is no fundamental research about performance evaluation of SFCLs for the dc grid. Therefore, we aim to verify the applicability of the conventional SFCL in HVDC grids and perform a comparative analysis of the performance of several types of SFCLs. To analyze the performance of the conventional SFCL in the HVDC grid, three well-known representative types of SFCLs are modeled in MATLAB/Simulink, and their current limiting and recovery characteristics and energy dissipation are examined in voltage-source converter HVDC system application. From the simulation results, we deduced the strengths and the weakness of different types of SFCLs. Consequently, the likely SFCL candidate for commercialization in dc grid applications is suggested.

Feasible Application Study of Several Types of Superconducting Fault Current Limiters in HVDC Grids

A new high-performance bridge-type fault current limiter (BFCL) is proposed in this study. The proposed BFCL can moderate transient overcurrent in abrupt load change condition and dramatically limit the fault current in fault condition. The key feature of this new BFCL is based on using a switched transformer-type DC reactor. In fact, the secondary side of the transformer is short-circuited during normal condition. Therefore, the transformer has negligible effect on the circuit in this condition. When the load current exceeds a predefined threshold (permissible maximum load current), secondary side of the transformer is opened by an insulated gate bipolar transistor. Consequently, inrush current of the load suppresses in abrupt load change condition or the current increases at a constant rate in fault condition. When current exceeds a higher predefined threshold (in the order of fault current), it is limited via the switched DC reactor and a discharging resistor. Analytical analysis of the proposed BFCL is presented in detail. Simulation and experimental results validate the effectiveness of this structure in abrupt load change and fault conditions.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2013.0276

Development of a high-performance bridge-type fault current limiter

This study deals with a developed thyristor based bridge-type fault current limiter (TBFCL), in which the main fault current limiting function is relegated to a limiting circuit controlled by a silicon controlled rectifier (SCR). Since SCR is a reliable power electronic switch and can be found in high ratings, the proposed TBFCL can be utilised in higher ratings in comparison with other proposed BFCLs. The TBFCL limits fault current in two steps; (i) by a fully controlled DC reactor during transient fault interval (ii) by a SCR based current limiting circuit during steady state fault interval. The TBFCL has a bridge-type DC reactor controlled by an isolated gate bipolar transistor and a current limiting circuit in parallel with the bridge controlled by a thyristor. Upon fault occurrence, the DC reactor limits increasing rate of the fault current, while the generated over voltage activates auto-triggering control circuit of the SCRs. Therefore, the fault current is limited through the SCR current limiting path and the DC reactor path is interrupted. Analysis of the proposed TBFCL is presented in detail. Simulation and experimental results verify the performance of the TBFCL.

Thyristor based bridge-type fault current limiter for fault current limiting capability enhancement

We propose a novel series transformer based diode-bridge-type solid state fault current limiter (SSFCL). To control the fault current, a series RLC branch is connected to the secondary side of an isolation series transformer. Based on this RLC branch, two current limiting modes are created. In the first mode, R and C are bypassed via a paralleled power electronic switch (insulated-gate bipolar transistor, IGBT) and L remains connected to the secondary side of the transformer as a DC reactor. In the second mode, the series reactor impedance is not enough to limit the fault current. In this case, the fault current can be controlled by selecting a proper on-off duration of the parallel IGBT, across the series damping resistor (R. and capacitor, which inserts high impedance into the line to limit the fault current. Then, by controlling the magnitude of the DC reactor current, the fault current is reduced and the voltage of the point of common coupling (PCC) is kept at an acceptable level. In addition, in the new SSFCL, the series RC branch, connected in parallel with the IGBT, serves as a snubber circuit for decreasing the transient recovery voltage (TRV) of the IGBT during on-off states. Therefore, the power quality indices can be improved. The measurement results of a built prototype are presented to support the simulation and theoretical studies. The proposed SSFCL can limit the fault current without any delay and successfully smooth the fault current waveform.

Series transformer based diode-bridge-type solid state fault current limiter

With the continuous expansion of power grid capacity, the problem of short-circuit current exceeding the standard is becoming increasingly serious. Fault current limiter is a promising solution and is gradually becoming a research hotspot. In this study, fault current limiters are classified into four categories. And saturated-core fault current limiters are emphatically introduced, including its working principle and comparison with the other three categories. Saturated core fault current limiters are divided into four branches according to the ways leading the core saturated. A comprehensive review of the research activities and emerging technologies of saturated-core fault current limiters for AC power systems is presented in this study. The working principle and typical structure of DC-biased-, permanent-magnet-, superconducting- and hybrid-type saturated-core fault current limiters are introduced. The advantages and disadvantages of four types of saturated core fault current limiters are compared in detail from the aspects of current-limiting performance, iron core size and DC magnetomotive force. Real grid application examples of some types of devices are presented, as well as new progress in the techniques, are covered and discussed in detail. One may find the content of this study helpful as a detailed literature review or as practical technical guidance.

Saturated-core fault current limiters for AC power systems: Towards reliable, economical and better performance application

This paper deals with design and operating tests of prototype hybrid superconducting fault current limiter (SFCL) which is series connected non-inductive solenoid resistive coil and asymmetric non-inductively wound coils. The role of resistive SFCL is for reducing the fault current in the first swing. Moreover, resistive SFCL can reduce a load of dielectric strength in hybrid SFCL. Two kinds of high temperature superconductor (HTS) wires were used to fabricate asymmetric HTS coil. These HTS wires had different quench characteristics such as different critical current and n-value. Unbalanced current distribution between two HTS wires in the asymmetric HTS coil during the fault should occur. Thus, the asymmetric HTS coil generates impedance and repulsive force from magnetic flux. The finite element method was performed to calculate maximum repulsive force. From experimental tests and FEM simulation results, proper combination of HTS wires and configuration of asymmetric HTS coil with fast switch were determined to increase maximum repulsive force. Also, the prototype hybrid SFCL with fast switch was fabricated and performed.

Kang Sik Ryu

Papers

Design and Tests of Prototype Hybrid Superconducting Fault Current Limiter With Fast Switch