An Adaptive Overcurrent Coordination Scheme to Improve Relay Sensitivity and Overcome Drawbacks due to Distributed Generation in Smart Grids

Distributed Generation (DG) brought new challenges for protection engineers since standard relay settings of traditional system may no longer function properly under increasing presence of DG. The extreme case is coordination loss between primary and backup relays. The directional overcurrent relay (DOCR) which is the most implemented protective device in the electrical network also suffers performance degradation in presence of DG. Therefore, this paper proposes the mitigation of DG impact on DOCR coordination employing adaptive protection scheme (APS) using differential evolution algorithm (DE) while improving overall sensitivity of relays . The impacts of DG prior and after the application of APS are presented based on interconnected 6 bus and IEEE 14 bus system. As a consequence, general sensitivity improvement and mitigation scheme is proposed

International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

Adaptive overcurrent protection application for a micro-grid system in South Africa

Abstract: The non-directional overcurrent protection (International Electrotechnical Commission standard IEC 617 or American National Standards Institute ANSI/Institute of Electrical and Electronic Engineers IEEE C37.2 standard device number 51) is one protection type/relay function that has stood the test of time. The latest generation of relays has brought about enhanced capabilities. The most popular overcurrent protection, which is the Inverse Definite Minimum Time (IDMT) function, has proven to provide coordination of electrical nodes with ease. This is one of the oldest but extremely reliable relay characteristic. A number of new protection functions and enhancements to existing functions are commensurate to the advanced technical capabilities of the newer generation protective devices. The new development techniques include “acceleration”, which is a technique of sending the circuit breaker status of the near end of a line or feeder to the far end to influence the relay decision at the far end. Impedance protection, unit line protection, etc. have come with many advanced characteristics and properties. The enhancements to protection devices bear special features but cannot substitute inverse time overcurrent protection, which, up to now, is a reliable backup in feeder protection schemes in South Africa. The superior feature is the capability to achieve coordination between a series of protective devices. This is achievable without excessive damage to the electrical components of the circuit...M.Ing. (Electrical Engineering

Recent Developments and Challenges on AC Microgrids Fault Detection and Protection Systems–A Review

The protection of AC microgrids (MGs) is an issue of paramount importance to ensure their reliable and safe operation. Designing reliable protection mechanism, however, is not a trivial task, as many practical issues need to be considered. The operation mode of MGs, which can be grid-connected or islanded, employed control strategy and practical limitations of the power electronic converters that are utilized to interface renewable energy sources and the grid, are some of the practical constraints that make fault detection, classification, and coordination in MGs different from legacy grid protection. This article aims to present the state-of-the-art of the latest research and developments, including the challenges and issues in the field of AC MG protection. A broad overview of the available fault detection, fault classification, and fault location techniques for AC MG protection and coordination are presented. Moreover, the available methods are classified, and their advantages and disadvantages are discussed

Real time adaptive relay settings for Microgrid protection verified using Hardware in Loop

Microgrids with penetration of renewables is imposing new challenges for system protection. Renewables are characterized with high source impedance which limit the short circuit current. The value of short-circuit current is limited due to converters used which limit the current to a maximum of 1.1 to 1.5 times maximum rated load current. This can result in faults during the islanded mode of microgrid to go unnoticed if the relay settings are not adapted to account for it. The presence of such uncleared faults in the microgrid can result in exposing it to overcurrent for a long time which can damage the equipment. One solution is to have different protection element pickup settings for different modes of operation. This report discusses the development of an algorithm to switch these settings upon microgrid state changes and test the algorithm using OPAL-RT hardware in loop real-time testing with SEL-351S relay as the hardware

Developing an adaptive protection scheme towards promoting the deployment of distributed renewable sources in modern distribution networks: operational simulation phase.

The large-scale integration of renewables into the electricity grid as distributed generation sources for providing clean energy supply together with the recent introduction of the smart grid concept, have accelerated the need to modernize the existing protection schemes to accommodate the challenges originated from distributed generation. This paper presents an adaptive protection scheme that has been developed to allow automatic adjustment of optimal relay settings in response to multiple network topologies and unexpected variations arising from renewable energy systems integration towards promoting their deployment in modern distribution networks. A Simulink model is developed to simulate the operation of the adaptive protection scheme, being interlinked to a linear-programming technique to allow optimizing the relay settings in response to dynamic changes of network topology associated with the integration of distributed generation sources. The performance of the developed adaptive protection scheme in accommodating the dynamic changes of network topology has been assessed under two proposed network topologies using a small-scale network that has been built in the lab as part of experimental work for the purpose of implementing the adaptive control unit. Results have demonstrated the effectiveness of the developed approach in optimizing the relay settings in response to the subjected topology changes, achieving minimum relay trip times while ensuring a suitable relay coordination is satisfied in each of the tested network topologies

Inter-trip links incorporated optimal protection coordination

Due to advances in smart grid, different communication links as delay, inter-trip and activation are used between relays to enhance the protection system performance. In this paper, the effect of inter-trip links on optimal coordination of directional overcurrent relays (DOCRs) is analytically investigated and modelled. Moreover, an index is proposed to find the optimum locations for inter-trip link installation to reach the minimal fault clearance times under the selectivity constraint. Then a method is proposed to determine the candidate locations of inter-trip links and the associated reduced operating times. An Exhaustive search approach is also used to validate the efficiency of the proposed method. The method is simulated and tested on distribution network of IEEE 33 bus using the Power Factory software and MATLAB optimization toolbox. Genetic algorithm is used as an optimization tool to find optimal settings of relays. The results indicate the capability of proposed method in optimal protection coordination with optimum inter-trips

Proposed adaptive overcurrent protective relaying in a reliable micro-grid system

Abstract: A refinement to the way that overcurrent (O/C) protection of Inverse Minimum Time (IDMT) characteristic is applied in order to achieve reliable operation of a power system that contains Distributed Generation (DG) is required. This system is a micro-grid system marred with complexities of bidirectional power flow which the earlier generations of relays were not capable of dealing with. This paper investigates the application of adaptive O/C protection for effective selectivity, proper co-ordination of tripping and generally, proper management of increased fault levels introduced with connection of DG into the grid. Incorrect tripping has always resulted in nuisance tripping of circuit breakers deterring productivity, upsetting end-users and even posing a risk to life. Directional overcurrent protection is applied in Intelligent Electronic Devices (IED’s) and prove through simulations that correct coordination of cascaded breakers in a mesh system is achieved with minimal disruption of supply. Different settings groups are applied to an IED relay and a seamless migration between settings groups is achieved though relay input logic

A review on protection issues in micro-grids embedded with distribution generations

© 2017 IEEE. According to recent developments, the application of distributed generations (DGs) has become popular especially in distribution systems. The high utilization of distributed generating resources in modern power systems can cause new challenges from protection coordination perspectives. Changing the distribution system structure from single-supply radial system to multi-source ring network, leads to the bidirectional power flow and also has a vital impact on protection coordination issues. In addition, micro-grids can be operated under grid-connected as well as islanded mode, and fault current is extensively different for these two operation modes. Therefore, traditional protection algorithms cannot be used in the advancement of power systems. In recent years, several research studies have been conducted to investigate the improvement of protection schemes in micro-grids. This paper presents a comprehensive review on protection problems resulting from micro-grids embedded with DGs, and discusses some alternate protection strategies