Distributed generation adverse impact on the distribution networks protection and its mitigation.

Integration of Distributed Generation (DG) generates problems for the protection of Distribution Networks (DNs) in power systems. When DG is integrated into a power distribution system (DS), the radial nature of the network is altered and the power starts to flow in a reverse direction. In addition to the reverse flow of power, the DG upsurges the fault current level and affects the existing time intermission coordination of the protective overcurrent relay. This study proposes a reverse power relay (RPR) and Fault Current Limiter (FCL) to mitigate the fault current level and reverse power flow in a Distribution Network (DN) by the use of DG. The FCL works only as a unidirectional fault current limiter (UFCL) by restricting the flow of fault current that occurs in the main grid (MG) of the DG. However, FCLs can protect the flow of fault currents from the MG by affecting the operational flexibility and reliability of the DG. To overcome the flow of fault current of the DG, this study proposes RPR to monitor the power flow to the DG. Collectively the study focuses on the protection of radial DS by using RPR and UFCL. The analysis and the modeling were conducted on the 15KV DN of the radial feeder in Debre Markos DN. The 3Φ fault analysis (which is more severe than others) was performed to validate the protection capability of the mitigation techniques which were proposed in this study.

Protection of Sensitive Loads in Distribution Systems Using a BSFCL-DVR System.

In this paper, an incorporated bridge-type superconducting fault current limiter (BSFCL) and Dynamic Voltage Restorer (DVR) is presented to improve the voltage quality and limiting fault current problems in distribution systems. In order to achieve these capabilities, the BSFCL and DVR are integrated through a common DC link as a BSFCL-DVR system. The FCL and DVR ports of the BSFCL-DVR system are located in the beginning and end of the sensitive loads' feeder integrated to the point of common coupling (PCC) in the distribution system. At first, the principle operation of the BSFCL-DVR is discussed. Then, a control system for the BSFCL-DVR system is designed to enhance the voltage quality and limit the fault current. Eventually, the efficiency of the BSFCL-DVR system is verified through the PSCAD/EMTDC simulation.

Numerical Study on Transient State of Inductive Fault Current Limiter Based on Field-Circuit Coupling Method.

As the capacity of the power grid continues to expand, high-level fault currents might be caused during a contingency, and the problem of short-circuit current over-limitation is imminent. The high-temperature superconducting (HTS) fault current limiter (FCL) is an effective method to solve this problem. In this paper, a transient numerical model for the process of limiting current in the inductive FCL is proposed. The model is based on the coupling of multiphysics finite element simulation and a circuit model. The voltage source is used as input, which can simulate the macroscopic characteristics in the process of limiting current, such as the voltage and current waveforms, and can also simulate microscopic characteristics, such as temperature, magnetic field, and electrodynamic force distribution. The short-circuit experimental data of an air core inductive superconducting fault current limiter (SFCL) prototype was compared with the simulation results to verify the reliability of the simulation.

Study of Resistive-Type Superconducting Fault Current Limiters for a Hybrid High Voltage Direct Current System.

In this paper, a hybrid high voltage direct current transmission system containing a line commutated converter and a voltage source converter is developed. To enhance the robustness of the hybrid transmission system against direct current short-circuit faults, resistive-type superconducting fault current limiters are applied, and the effectiveness of this approach is assessed. Related mathematical models are built, and the theoretical functions of the proposed approach are expounded. According to the transient simulations in MATLAB software, the results demonstrate that: (i) The superconducting fault current limiter at the voltage source converter station enables to very efficiently mitigate the fault transients, and owns an enhanced current-limiting ability for handling the short-line faults. (ii) The superconducting fault current limiter at the line commutated converter station is able to mildly limit the fault current and alleviate the voltage drop, and its working performance has a low sensitivity to the fault location. At the end of the study, a brief scheme design of the resistive-type superconducting fault current limiters is achieved. In conclusion, the application feasibility of the proposed approach is well confirmed.

Power flow analysis and optimal locations of resistive type superconducting fault current limiters.

Based on conventional approaches for the integration of resistive-type superconducting fault current limiters (SFCLs) on electric distribution networks, SFCL models largely rely on the insertion of a step or exponential resistance that is determined by a predefined quenching time. In this paper, we expand the scope of the aforementioned models by considering the actual behaviour of an SFCL in terms of the temperature dynamic power-law dependence between the electrical field and the current density, characteristic of high temperature superconductors. Our results are compared to the 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, to study the impact of these protection strategies on the performance of the overall electricity network. As a representative renewable energy source, a 90 MVA wind farm was considered for the simulations. Three fault conditions were 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 estimations of reliability and determining the optimal locations of resistive type SFCLs in distributed power networks. Our results may help decision making by distribution network operators regarding investment and promotion of SFCL technologies, as it is possible to determine the maximum number of SFCLs necessary to protect against different fault conditions at multiple locations.

An improved low-voltage ride-through performance of DFIG based wind plant using stator dynamic composite fault current limiter.

In this paper, an enhanced low-voltage ride-through (LVRT) performance of a grid connected doubly fed induction generator (DFIG) has been presented with the usage of stator dynamic composite fault current limiter (SDCFCL). This protection circuit comprises of a suitable series resistor-inductor combination and parallel bidirectional semiconductor switch. The SDCFCL facilitates double benefits such as reduction of rotor induced open circuit voltage due to increased value of stator total inductance and concurrent increase of rotor impedance. Both effects will limit rotor circuit over current and over voltage situation more secured way in comparison to the conventional scheme like the dynamic rotor current limiter (RCL) during any type of fault situation. The proposed concept is validated through the simulation study of the grid integrated 2.0MW DFIG.