Centralized Protection Scheme Research Articles

Short-Circuit Protection Schemes for LVDC Microgrids Based on the Combination of Hybrid Circuit Breakers and Mechanical Breakers

In recent years, low-voltage direct current (LVDC) microgrids are becoming more attractive because they represent a solution to integrate renewable sources, storage, and electronic loads bringing some advantages in comparison with traditional AC grids. However, the protection of such a network involves many challenges, especially in the case of LVDC microgrids with more than one feeder and multiple energy sources. Indeed, the traditional protection breakers used for an AC grid cannot isolate the faults and protect the components of a DC grid, while the use of solid-state circuit breakers increases energy losses. This paper deals with the analysis and design of the protection schemes for LVDC microgrids through the combination of mechanical circuit breakers and hybrid circuit breakers. This solution has the advantage of energy loss reduction but introduces further issues due to the slow transition times of the mechanical circuit breakers. Thus, a completely decentralized control system capable of overcoming the fast fault-clearing time, cost-effectiveness, and selectivity issues is designed to protect from pole-to-pole faults. The proposed control strategy is compared with a centralized protection scheme available in the literature through numerical simulation. The two algorithms show similar performances, with a mean voltage dip duration of less than 30 ms and a maximum voltage dip duration of about 100 ms in the most severe fault condition, but the proposed solution is more reliable and flexible since it does not depend on the communication system.

A Cosine Similarity-Based Centralized Protection Scheme for dc Microgrids

Unlike the phasor measurement-based protection in ac systems, the protection of dc systems deals with complex fault transients which mandate the isolation of the faulted segment within few milliseconds as continued fault current leads to overheating issue in power electronic converters. To this end, several works have been suggested-based on the unit and nonunit protections for dc microgrids. Threshold selection and protection coordination are the challenges associated with nonunit protection. Similarly, communication delay and link failure limit the application of unit protection. To address these issues, this article presents a robust centralized protection scheme for dc microgrids, which is resilient to communication delay and link failure. It uses the current of each line segment to compute the similarity of current change at both ends of the line segment to derive the protection decision. To overcome the communication failure from one end of the line segment or even from multiple segments, the proposed method uses data from adjacent segments to derive the protection decision correctly. Using power systems computer aided design (PSCAD)/electromagnetic transients and direct current (EMTDC) environment, the performance of the proposed method is evaluated for various cases and compared with available techniques. Finally, the accuracy of the protection algorithm is validated under experimental conditions.

IEC 61850-Based Centralized Protection against Single Line-To-Ground Faults in Ungrounded Distribution Systems

We developed an International Electrotechnical Commission (IEC) 61850-based centralized protection scheme to prevent single line-to-ground (SLG) faults in the feeders and busbars of ungrounded distribution systems. Each feeder intelligent electronic device (IED) measures its zero-sequence current and voltage signals and periodically transmits zero-sequence phasors to a central IED via a Generic Oriented Object Substation Event message. Using the zero-sequence phasors, the central IED detects SLG faults in feeders and busbars. To achieve centralized protection, angle differences between the zero-sequence currents and voltage phasors are exploited, and their calculation compensates for data desynchronization. The feeder IEDs were implemented using the MMS-EASE Lite library, while the transmitted zero-sequence phasors were calculated based on fault signals simulated by Power System Computer Aided Design / Electro-Magnetic Transient Design and Control (PSCAD/EMTDC). The central IED determined if the SLG fault was in a feeder or busbar by aggregating and analyzing the zero-sequence phasors received from the feeder IEDs. The results confirmed the validity and efficiency of our centralized protection scheme.

Research on regional centralized protection scheme for distribution network integrated with electric vehicles

In view of the difficulty in balancing between selectivity and sensitivity of current protection in distribution networks integrated with electric vehicles, a regional current protection method applicable to distribution networks with large-scale electric vehicle penetration is proposed. First, considering the effect of the converter control strategy of electric vehicle chargers, a theoretical analysis is made to determine the expression of the short circuit current that the electric vehicle charger provides when faults occur on feeders. On this basis, according to the minimum short circuit current, the current protection criterion that meets the requirement of sensitivity alone is established. And then, combining multiple start-up signals of the criterion on the fault line and multiple-level neighboring lines after fault occurs, the regional current protection scheme for distribution network is constructed. Finally, simulation tests conducted in Real-Time Digital Simulator (RTDS) of IEEE 33-bus system verify that the proposed method can effectively avoid mal-cooperation between different protection zones which is common in traditional current protection. Besides, the proposed scheme is not affected by factors such as the charging capacity of electric vehicles, the number and the location of charging facilities, etc., and can accurately identify the fault location even when the information is partly missing or in error.

MVDC Microgrid Protection Using a Centralized Communication With a Localized Backup Scheme of Adaptive Parameters

The paper proposes a centralized protection scheme with a localized backup for a MVDC microgrid. The centralized scheme is implemented using the percentage differential current approach backed up with a localized scheme employing running autoregressive smoothing average. An adaptive mathematical analysis of the parameters employed is performed for a justified assent. The proposed scheme is ratified to be accurate and immune to the system configuration, voltage fluctuations, and high-resistance faults with its security, dependability, and selectivity validated for different transients and fault contingencies employing minimum solid state circuit breakers in the microgrid.

Centralized protection scheme for smart grid integrated with multiple renewable resources using Internet of Energy

Transmission and subtransmission lines in smart grid systems are designed as multitapped lines to supply loads or integrate wind or solar farms as medium-sized generation technologies. Transmission lines with multiple taps are an economical solution to prevent building new substations. However, these types of tapped lines create operational and protection challenges. When renewable resources are added to feeders, they act as transmission lines where energy flows in either direction in protection relays. Then, fault current flows in different directions and the coordination protection for this configuration fails. Modern protection schemes based on standalone decisions are not suitable in such cases, and new system protection methods should be devised. A key factor for future energy supply is information and communication technology based on the Internet of Energy (IoE), which is utilized to exchange information among all measurements on transmission and subtransmission systems in an environmental domain for accurate unit protection and the optimization of the coordination process. This information is collected by employing integrated electronic devices (IEDs). In such cases, the data measured by IEDs and exchanged in the environmental domain using IoE can achieve accurate unit protection for optimizing the coordination process. This system is a new development in the protection field using informatics; it is named i-protection. i-protection provides a novel method of accurately detecting faults using IEDs and IoE through wide-area wireless networks such as the IEEE 802.16 WiMAX technology. This is the first study to apply i-protection for protecting complex configurations with multiple taps at two different levels, i.e., transmission and subtransmission. The protection method considers the studied power system as one zone rather than multiple separate protection zones, which are used by conventional protection. The results show that the proposed protection method can successfully detect all types of faults in complex multitapped transmission lines with renewable resources. Moreover, the initial results indicate that the IEEE 802.16 network can meet the latency requirement of the proposed protection scheme.

Resilient Protection System Through Centralized Substation Protection

Power systems are experiencing drastic changes with the introduction of renewables and customer owned resources. These changes introduce new challenges in protection, control, and operation of power systems. In protection, it is necessary to develop new methods that are immune to the new characteristics and they avoid relay misoperations. In particular, any protection system is vulnerable to hidden failures. This paper introduces a new dynamic state estimation-based centralized protection scheme (DSEBCPS) at a substation level. The system supplements dynamic state estimation-based protection for individual zones known as “setting-less relays” to secure their operation against hidden failures. The DSEBCPS communicates with the setting-less relays via the station bus and obtains essential information from each protection zone, such as phasor quantities and breakers/disconnects status. This information is processed by the DSEBCPS to estimate substation topology and states. Specifically, the DSEBCPS performs dynamic state estimation in the quasi dynamic domain once per cycle to detect any abnormality within the substation. Upon detecting abnormalities, the DSEBCPS performs hypothesis testing to identify the source of the abnormality, that is, a fault or a hidden failure. Upon detecting a hidden failure, the DSEBCPS identifies the compromised data, replaces this data with estimated values by using the substation estimated states and model. The corrected data are used by the setting-less relays, enabling self-healing characteristics. The proposed capability to detect hidden failures and correct the effects of these failures in real time makes the setting-less relays secure against misoperations and bridges a critical gap in protection systems. This capability is demonstrated through numerical experiments that include several scenarios of hidden failures. The integration of the proposed scheme with the individual protection zone relays form a resilient protection and control system, which is self-immunized against hidden failures.

Design and testing of a centralized protection scheme for micro-grids

Micro-grids comprise low voltage distribution systems with distributed energy resources (DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from “connect and forget” philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units (PMUs) and a central protection unit (CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values (upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration (such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIgSILENT PowerFactory and MATLAB software packages.

Survivable wavelength-division multiplexing passive optical network system with centralized protection routing scheme and efficient wavelength utilization

A survivable wavelength-division multiplexing passive optical network (WDM-PON) with centralized protection scheme and colorless optical network units is proposed. The sideband channels generated via optical carrier suppression technique are used to carry both the downstream (DS) and the upstream (US) remodulated signals for two neighboring sub-PONs. By employing alternate path routing of sideband channels, the centralized protection scheme can provide reliable protection against any failure in feed fibers, remote node, and distribution fibers. The number of extra fibers is greatly reduced, and efficient utilization of wavelength resource is achieved. The feasibility of the proposed system is verified by 10-Gb/s DS and 1.25-Gb/s US signals over 25-km single-mode fiber transmission in both working and protection modes.

Adaptive centralized protection scheme for distribution systems with DG using risk analysis for protective devices placement

Conventional electric distribution systems are radial in nature, supplied at one end through a main source. These networks generally have a simple protection system usually implemented using fuses, re-closers, and over-current relays. Recently, great attention has been paid to applying Distributed Generation (DG) throughout electric distribution systems. Presence of such generation in a network leads to losing coordination of protection devices. Therefore, it is desired to develop an algorithm which is capable of protecting distribution systems that include DG, through diagnosis and isolation of faults. A new approach for the protection of distribution networks in the presence of DGs is presented in this paper. The algorithm is based on dividing an existing distribution network into several zones, each capable of operating in island operation. In the suggested method, risk analysis is used to optimize the protection zones by optimal placement of protective devices. Multilayer Perceptrons (MLPs) neural networks are used for determination of faults. The proposed scheme has been implemented on a selected part of a real distribution network of a large city and a MATLAB based developed software has been used to implement the proposed algorithm on the real network data.