Fault Protection Algorithm Research Articles

Ground fault protection algorithm of active distribution network based on energy extremum direction

AbstractAfter large‐scale distributed power sources are connected to the distribution network, the fault current undergoes noticeable changes, affecting the accuracy of traditional single‐phase grounding fault algorithms. Therefore, the objective of this paper is to address the impact of distributed power integration on the grounding algorithms of distribution networks. The main contribution is: by establishing an electrical system structure and model for distribution network grounding faults that include distributed generation (DG), theoretically deriving and calculating the transient zero‐sequence current frequency changes at the moment of fault, analysing the directional characteristics of zero‐sequence currents under DG connection conditions, designing a local grounding fault judgment algorithm based on energy extremum direction, and providing a fault judgment and isolation process for grounding fault monitoring devices. The results show: through simulation and experimentation, the algorithm was tested, and the method can reliably judge grounding faults under various transition resistances, different numbers and capacities of connected distributed power sources, and different grounding switch‐on angles. The applicability of the algorithm covers both methods of neutral grounding through an arc suppression coil and ungrounded neutrals, adapting to scenarios with or without DG connections.

Development of a Novel Backup Fault Protection Algorithm for Low-Voltage DC Microgrids based on Local Measurements and Chi-square Statistics

Development of a Novel Backup Fault Protection Algorithm for Low-Voltage DC Microgrids based on Local Measurements and Chi-square Statistics

A stepwise methodology for the design and evaluation of protection strategies in LVDC microgrids

Over the past years, there has been an increasing scientific interest in Low Voltage DC grids as an alternative to traditional Low Voltage AC grids, driven by the energy transition. However, fault detection and protection of LVDC microgrids still poses an important challenge for their breakthrough on a large scale. Due to the required speed and reliability of LVDC microgrid protection, an increasing amount of research is focussing on local, measurement-based protection algorithms. While several solutions for such a local, measurement-based fault protection algorithm have been proposed in literature, the design process of these algorithms is often unclear. As a result, it is often not straightforward to an LVDC grid designer how to tackle the design of an LVDC microgrid protection strategy. Furthermore, the framework within which the proposed algorithms are designed is often not discussed, as well as how well the algorithm will perform when the fault conditions deviate from this reference framework. Therefore, this paper presents a stepwise methodology for the design of fault protection strategies in LVDC microgrids with the aim of making this design process more straightforward and transparent. Furthermore, the proposed methodology allows to evaluate the robustness and boundaries of the designed protection strategy easily. The different steps of the methodology are discussed in detail and applied to a case study, followed by a sensitivity analysis of the developed protection algorithm to investigate its boundaries and improve its robustness.

ANN‐based robust DC fault protection algorithm for MMC high‐voltage direct current grids

Fast and reliable protection is a significant technical challenge in the modular multilevel converter (MMC)-based DC grids. The existing fault detection methods suffer from the difficulty in setting protective thresholds, incomplete function, insensitivity to high-resistance faults and vulnerable to noise. This study proposes an artificial neural network (ANN)-based method to enable DC bus protection and DC line protection for DC grids. The transient characteristics of DC voltages are analysed during DC faults. On the basis of the analysis, the discrete wavelet transform is used as an extractor of distinctive features at the input of the ANN. Both frequency-domain and time-domain components are selected as input vectors. A large number of offline data considering the impact of noise is employed to train the ANN. The outputs of the ANN are used to trigger the DC line and DC bus protections and select the faulted poles. The proposed method is tested in a four-terminal MMC-based DC grid under PSCAD/EMTDC. The simulation results verify the effectiveness of the proposed method in fault identification and the selection of the faulty pole. The intelligent algorithm-based protection scheme has good performance concerning selectivity, reliability, robustness to noise and fast action.

An Improved DC Fault Protection Algorithm for MMC HVDC Grids Based on Modal-Domain Analysis

To detect the dc faults for the modular multilevel converter (MMC)-based dc grids using overhead line transmission, many protection methods in phase-domain have been proposed. These existing protection methods suffer from incomplete function, weak theoretical basis, and sensitivity to fault resistance and noise disturbance. To overcome these shortcomings, this article proposes an improved dc fault protection algorithm using the modal-domain approach for the MMC-based overhead dc grids, which decouples the interaction between positive and negative poles and mitigates the strong frequency dependence of the characteristic impedance in phase-domain. The dc fault equivalent circuits are established in modal-domain and the fault characteristics during the initial stage are analyzed. Based on the modal-domain analysis, the line-mode reactor voltage which combines the fault characteristics of negative and positive reactor voltages is used to identify the internal faults. The zero-mode reactor voltage which enlarges the differences between faulty and healthy poles is used to select the faulted pole. This method is robust to fault resistance and noise with high detection speed. In addition, it is not affected by power reversal, ac faults, and dc circuit breaker (DCCB) operation, which are validated and evaluated by the simulations in PSCAD/EMTDC.

Novel Earth Fault Protection Algorithm Based on MV Cable Screen Zero Sequence Current Filter

This paper presents novel zero sequence current filter and earth fault protection relay, which utilize cable screens earthing current in protection algorithm. Different problems connected with state of the art of zero sequence current filters and protection relays are presented and compared with the proposed solution. The presented concept is verified in PowerFactory simulation software, experiment concerning modeling the earth fault current flow in medium voltage (MV) cable supplied from the low voltage (LV) network and measurements in the MV network in the Polish distribution system. The proposed solution is characterized by higher sensitivity and reduced number of erroneous trips. The presented solution is suitable for any MV cable lines. Biggest advantages are observed in power output lines from renewable energy sources, which are often operated under no-load conditions.

A novel fault protection system using communication-assisted digital relays for AC microgrids having a multiple grounding system

Abstract This paper develops a novel fault protection system for AC microgrids having a multiple grounding system. Communication-supported digital relays which have different protection modules are used for this novel microgrid protection system. The protection modules in a digital relay have various functionalities to protect AC microgrids from various fault types, such as: low/high-impedance ground faults and short-circuits. To effectively use the developed novel microgrid protection system, the first step is to reconfigure different microgrid structures into a standard microgrid configuration having a multiple-grounding system through using delta/wye-grounded or wye-grounded/wye-grounded transformers. Then, a fast–dependable–adaptable (FDA) fault protection algorithm is developed to protect AC microgrids from faults occurring at trunk lines, common buses or branch lines. At an islanded operation mode of AC microgrids, by using digital relays, a new protection module is designed to detect, locate, and classify the faults occurring at trunk lines and common AC buses, while other protection modules can use the existing protection methodologies (e.g. directional/non-directional overcurrent protection principles, etc.) to detect and clear the faults at source branches or load branches of the microgrids. At a grid-connected operation mode, standard overcurrent protection modules are applied for the FDA fault protection system. Simulation and experiment results obtained from various fault cases at a real low-voltage AC microgrid have validated the effective operation of the FDA fault protection system.

Investigate dynamic and transient characteristics of microgrid operation and develop a fast-scalable-adaptable algorithm for fault protection system

A microgrid (MG) system mainly consists of renewable energy sources, distributed generators, loads and energy storage devices. Development of the microgrid brings some emerging challenges. One of them is a microgrid fault protection system. In order to develop an optimal fault protection algorithm, this paper surveys dynamic and transient behaviours with respect to two operation modes of a microgrid, namely, islanded and grid-connected modes. Modelling and simulation of the MG's operation are performed by PSCAD/EMTDC software. A surveyed typical MG structure includes one dispatchable power source of microturbine (μT) system, another non-dispatchable power source of photovoltaic (PV) generation system and one battery power conditioning system (PCS). Whereas dynamic characteristics of the MG are investigated in cases of power change of loads or sources and motor starting, transient properties are surveyed through staged fault tests (e.g. single-phase and three-phase to ground faults) and the MG's operation transition between grid-connected and islanded modes. Simulation results are compared to actual experiment results performed at a 380V microgrid at Institute of Nuclear Energy Research (INER), Taiwan. From achieved dynamic and transient properties, this paper proposes a fast-scalable-adaptable (FSA) computing algorithm for a fault protection system to improve MG's reliability and adaptability operation. This new algorithm uses parameters of current, voltage and angle phase along with a communication network to protect online the microgrid. The proposed algorithm can solve challenging problems of high penetration of inverter-based distributed generators, reduced fault current values and non-directional power flow. Moreover, the algorithm can get a critical fault clearing time within one fault cycle, high accuracy and reliability for fault detection, identification of different types of faults and optimal isolation of faulted zones. Simulation and experiment results validate the proposed fast-scalable-adaptable fault protection algorithm.