Protection System Of Distribution Network Research Articles

Impact of distributed generation on the protection systems of distribution networks: analysis and remedies – review paper

Power networks, especially distribution networks, have been undergoing substantial changes since the application of new technologies. Technology development in the early part of the 21st century has opened up new horizons for automated, efficient and reliable power grids. New technologies, while enhancing the capability of the electrical networks and providing opportunities and innovative solutions to the challenges of future networks, can also cause drawbacks that should be investigated and taken into account. Distributed generation (DG) is one of the new technologies that improves the operation of power grids. Despite tangible benefits that integration of DG units brings to electrical grids, their notable impacts on protection systems of power networks raise many challenges and concerns on how a fault should be detected and isolated in active distribution networks. Many attempts have been made to investigate the downside of the interconnection of DG units and methods to mitigate their impacts have been proposed. This study reviews the impact of DG integration on protection systems addressed in other research works and recapitulates suggested methods provided by scholars.

A multi-agent-based integrated self-healing and adaptive protection system for power distribution systems with distributed generation

The development of self-healing systems in the context of power distribution networks has increased significantly over the last years. However, such feature causes changes in the power grid structure, which may affect the coordination of protection systems. This work proposes a self-healing system (SHS) integrated with an adaptive protection system (APS) based on multi-agent systems (MAS). This approach aims at minimizing adverse impacts caused by the network restoration on the protection systems of distribution networks that contain distributed generation (DG). The SHS uses negotiation among agents to maximize the number of restored loads, while the agents of the APS reset the protection settings after changes occur in the network topology and state of DGs. The APS is capable of changing the current setting group and, if necessary, calculating new settings that can be sent to the relays to ensure the accurate coordination of protection systems. The proposed schemes are evaluated in a test workbench using commercial digital relays in different scenarios comprising DG penetration levels and network topology changes. The results clearly demonstrate that this strategy is fast and reliable when enhancing and providing robustness to the self-healing procedure.

Minimising direct‐coupled distributed synchronous generators impact on electric power systems protection

This study presents a method to place, size, coordinate and adequate protection systems in distribution networks (DNs) with directly-coupled distributed generation (DG). DG penetration increase in DNs is beneficial to the operation of these grids. However, since the majority of DN is already consolidated, with protective devices sized for certain current levels and directionality, adding DG to these systems may cause issues. This study introduces a method to determine protective devices placement, their coordination and sizing, depending on DG location. Direct-coupled DG is considered since DG connected to DNs through power electronics limit the fault current to the network. Firstly, recloser allocation is treated in a multiobjective approach, reducing reliability indices. To solve this problem, particle swarm optimization is applied. Fuse cutouts allocation is determined by a set of rules, developed considering feeder particularities. After, DG is considered and its effects on the protection coordination are evaluated. To adapt DN to receive DG, fault current limiters are placed to avoid recloser – fuse miscoordination. Finally, recloser operation is analyzed to determine the operational philosophy to avoid misoperation in the presence of DG. Graphical and numerical results are presented for test systems to show the functionality and performance of the proposed method.

Integration and Evaluation of the Impact of Distributed Generation on the Protection System of Distribution Network with DG Using Etap

Distributed Generation (DG) has been growing rapidly in deregulated power systems due to their potential solutions to meeting localized demands at distribution level and to mitigate limited transmission capacities from centralized power stations. Penetration of DG into an existing distribution system has so many impacts on the system. Despite the benefits a DG will provide; it has a negative impact on the power system protection, thus affecting both reliability and stability of the system. This paper evaluates the impact of DG on the power protection systems with DG integrated in the systems. IEEE 33 Bus system was modelled in full operational details using ETAP. Protection coordination was carried out using Modified PSO. To investigate the impact of DG on the protection systems, different fault scenario have been simulated with and without DG installed. The fault current level, false tripping, unintentional islanding, and behavior of the existing protection system were investigated considering two scenarios. Case one was the integration of single DG while case two was the integration of two DGs. The type of DG integrated was solar photovoltaic. Simulation results revealed that the fault current level for a 3 phase fault at bus 27 for the system increases by 2.5% for case one and 24% for case two. There was unitentational islanding and false tripping as a result of the current contribution from the DG. The sequence of operation of the protective devices clearly showed that there was mis coordination of the protective devices.

A Multiobjective Optimization Technique to Develop Protection Systems of Distribution Networks With Distributed Generation

This paper presents a new methodology based on multiobjective optimization techniques to perform an optimized, coordinated, and selective allocation of control and protection devices in distribution networks with distributed generation (DG). The proposed mathematical model consists of two objective functions that consider economic issues and the network continuity index. Physical and operational constraints are taken into account, with emphasis on the set of constraints based on practical rules of distribution companies and international technical standards, which require the specification, coordination, and selectivity of the protection devices installed in the network. The possibility of load transfer from neighboring feeders and islanded DG operation is also considered. The proposed model is a mixed integer nonlinear programming, and we use NSGA-II (Nondominated Sorting Genetic Algorithm) to solve it. The proposed methodology is applied in a real 135-bus system found in the literature.

Intra-minutes technical impacts of PV grid integration on distribution network operation of a rural community under extreme PV power delivery

Integration of PV systems with distribution networks causes some technical challenges to the electrical grid and the distribution network. Most of the conducted researches concentrate on the long horizon impacts (hourly and daily based data). This study aims to capture the extreme technical impacts of PV grid integration on the distribution network at small time scale (few minutes) such that optimum mitigation techniques can be selected. The study assumes that the instantaneous peak power that would be generated from the PV array is considered constant (does not vary) for a small time frame such that the distribution network is subjected to the ultimate possible impacts (extreme impacts). Consequently, the extreme impacts are determined when the PV array produces the peak (extreme) power corresponding to the rating of installed PV array. The paper investigates the influence of both PV size (penetration level) and PV location (siting) on several technical issues such as: voltage profile at different buses, power losses across cables and short circuit currents at different nodes subjected to symmetrical fault conditions. In addition, the impacts on the total harmonic distortion (THD) of buses voltages and currents have been computed. The 3-Φ grid-connected inverter is controlled by instantaneous power control strategy to adjust the penetration level to the desired value. The obtained results indicate that the increase in PV penetration level improves the voltage profile along the network nodes and leads to a reduction in power losses across the cables as well. However, the PV grid integration has adverse effects on the distribution network protection system since the increase in PV penetration level results in higher values of the short circuit currents under symmetrical fault conditions compared with the network without renewable resource. Accordingly, the settings of overcurrent relays have to be revised to handle the under-reach (blinding of protection) or over-reach (sympathetic tripping) conditions of the relaying protection system. Moreover, the obtained results indicate that the THDs are negatively affected by the increase of the penetration level. Owing to the results, the PV allocation (PV injecting node) has also its own effects on the distribution network. The overall system is investigated using professional version of PSIM.

Protection coordination scheme for distribution networks with high penetration of photovoltaic generators

The installation of photovoltaic (PV) systems is gaining great attention due to the matured PV technology and the lowered price of PV modules. With an increasing penetration of PV systems, the selectivity of distribution network protection may be affected which results in undesirable de-energisation of loads, damage of network equipment, and reduction of reliability. This study presents a method to preserve the protection coordination considering future PV systems installation with any penetration level and different locations along the distribution feeder. Depending on the accessibility of protection device settings or PV control parameters, the proposed method modifies the existing characteristic curve of overcurrent devices or limits the output current of PV sources, respectively. The proposed strategy does not change the structure of existing distribution network protection system and can also be implemented in the old and non-programmable relays. Meanwhile, it does not need the communication links. The merits of the proposed method are demonstrated through several case studies using the Isfahan distribution network.

Analysis of the impact of connecting a larger number of small hydroelectric power plants to the short-circuit currents values and relay protection system of distribution network

In this paper the influence of a large number of small hydro power plants on the short-circuit currents is analysed, as well as the operation of the relay protection system within the real distribution network in Serbia. The necessary modification of the existing protection functions, as well as the implementation of the new proposed protection functions, are presented and discussed. Network modeling and analysis are performed using the program tool DIgSILENT PowerFactory.

Practical Impact of Not Self-disconnected VSPP During Faults and Unintentional Islanding on Distribution System Reliability

The promotion of small-scaled distributed generation (DG), commonly known as Very Small Power Producer (VSPP) in Thailand's electric power industry, is derived from its incentive policy, energy efficiency, and environmentally friendly attribute. For this reason, distribution networks have seen a high penetration level of VSPPs powered by conventional or renewable energy resources. Although VSPPs have economic and environmental benefit of the sustainable energy, they have imposed technical barriers and established new requirements for control and protection system of the distribution networks. This paper investigates the possible negative impacts of VSPPs on control and protection systems of distribution networks located in a metropolitan area. Three case studies of real, existing VSPP in 24kV distribution network are practically presented with short-circuit analysis and dynamic analysis primarily focusing on undisconnected VSPP during faults, and unintentional islanding. The study results show that without proper measures to address the issues on the existing control and protection system, the distribution network would be unable to maintain its integrity of electricity power supply for disturbance incidents.

Automation and monitoring of the distribution network in presence of distributed generations by using Petri Nets

Considering the fact that the main part of electrical energy losses is related to the distribution level; therefore, controlling and monitoring of this part of the network is necessary to reduce energy losses which is made possible through distribution automation. Distribution automation systems need decision making regarding the responsibilities being performed by operators. On the other hand, there is the possibility of incorrect decision making by operators due to the large volume of information and decision making time shortage during automation steps which can be created by incorrect information received from the network and consequently causes the incorrect control command sending to distribution network devices. Also, introducing the Distributed Generations (DGs) in the protection system of distribution network, it is possible for the protective devices to have an incorrect operation which affects the operators' decisions performed by the automation system. In this paper, a new Petri-Net modeling method is used to make the distribution network monitoring and automation possible and also to help the operator in correct decision making. In addition, the protective devices' operation is determined more reliably using the attained data from the automation system.