Assessing Feasibility of Deploying Distance Protection within Underground Medium Voltage Distribution Network

Distance protection is not utilized in distribution networks, unlike the transmission systems, due to the inherent characteristic of the distribution networks and the additional required facilities of the distance protection, compared with over-current protection, which is in use in the distribution systems. This paper studies the measured impedance at the source node of a distribution feeder with dispersed generation (DG) unit. The ideal tripping characteristic is presented for the distribution feeder with DG unit. The variation of this tripping characteristic is investigated as a function of DG unit parameters. The especial case of the absence of the fault resistance is highlighted.

Market-Based Coordination of Transmission and Distribution Network Planning with Distributed Energy Resources Planning

The electric power grid is undergoing a tremendous transformation due to the increasing penetration of renewable energy resources beginning with wind and more recently with the distributed energy resources (DERs) such as solar and battery storage. DERs have dramatically changed the role of the distribution systems in the overall power grid, and they are expected to contribute a significant portion of power generation in the future. If current trends for DERs continue, system operation and control will need to change dramatically for improved grid reliability and resiliency. As renewable resources increase in penetration, new and challenging operational, planning, and design problems are expected to emerge. Some of the key challenges that arise in the planning and operation of the future grid are: 1) Quantifying the impact of high DER penetration in distribution systems on bulk grid behavior over multiple time scales. 2) Identifying whether a particular DER configuration/settings have a large impact on the overall grid behavior. These challenges can be addressed in an offline manner using detailed T&D grid models and they can also be addressed in an online manner using sensor measurements. In particular, the advancement and planned growth in sensor technology in power grid over various voltage levels provide us with a unique opportunity to tackle these challenges from a data analytic perspective without needing detailed T&D grid models. A few questions that naturally arise when addressing the challenges from DERs using sensor data are: 1) How can we use limited sensor measurements to monitor & control voltage stability and small signal stability of the bulk system? 2) How can we ensure that the developed data analytic methods are robust to data availability and quality issues? 3) How can we compute the developed analytics in a scalable manner using streaming measurements? In this project, we addressed the aforementioned challenges arising from DERs and answered the questions raised above on how to effectively use the sensor measurements to enhance the reliability and performance of the electric grid. Thus, the overarching goal of this project is to develop effective reduced/representative system models from data that make the computational complexity sufficiently manageable so as to be useful to simulate, analyze, and even control complex non-linear power systems dynamics with large penetrations of DERs. In order to achieve the objective, the project team established a four-fold technical approach 1) Formulated a combined transmission-distribution co-simulation framework for data generation and validation, 2) Derived reduced/representative models of power systems based on data-driven methods for efficient computation and appropriate representation of system behavior, 3) Developed data driven characterization of power system behavior based on transfer operator theory, machine learning and optimization for model estimation, 4) Incorporated a scalable data management and processing architecture using distributed Kafka streaming applications that coordinate input data streams to the developed data analytics. The key accomplishments of the project are: 1) Development of a scalable multi-timescale T&D co-simulation framework (both for steady state and for dynamic co-simulation) using commercial solvers (PSSE and GridLAB-D). The steady-state T&D co-simulation interface is shared with our industry partner (PJM). 2) A structured reduced order dynamic model of distribution systems that can represent partial motor stalling along with a systematic procedure to derive the model parameters. 3) A PMU based online method to monitor, localize and mitigate fault-induced delayed voltage recovery using DER reactive support and load control in distribution systems. 4) Development of linear operator based robust methodologies for dynamic state estimation, uncertainty quantification, system identification and trajectory prediction for power system dynamics. 5) An adaptive damping control for utilizing wind energy resources to provide oscillation damping and system stability. 6) Implementation of Kafka-based framework for efficient processing of streaming data using Linux-based local virtual environment.

A challenge in transmission-distribution coordination is how to quickly and reliably coordinate Distributed Energy Resources (DERs) across large multi-stakeholder Distribution Networks (DNs) to support the Transmission Network (TN), while ensuring operational constraints continue to be met within the DN. Here we propose a hierarchical feedback-based control architecture for coordination of DERs in DNs, enabling the DN to quickly respond to power set-point requests from the Transmission System Operator (TSO) while maintaining local DN constraints. Our scheme allows for multiple independently-managed areas within the DN to optimize their local resources while coordinating to support the TN, and while maintaining data privacy; the only required inter-area communication is between physically adjacent areas within the DN control hierarchy. We conduct a rigorous stability analysis, establishing intuitive conditions for closed-loop stability, and provide detailed tuning recommendations. The proposal is validated via case studies on multiple feeders, including IEEE-123 and IEEE-8500, using a custom MATLAB-based application which integrates with OpenDSS. The simulation results show that the proposed structure is highly scalable and can quickly coordinate DERs in response to TSO commands, while responding to local disturbances within the DN and maintaining DN operational limits.

FERC Order No. 2222 was issued to remove barriers to integrating distributed energy resources (DERs) into wholesale electricity markets and improve economic incentives for their adoption, which promotes benefits such as enhanced operational efficiency, reduced carbon emissions, and lower consumer costs. However, integrating DERs presents significant techno-economic challenges due to their unique characteristics compared to conventional generators. Existing wholesale markets primarily accommodate large generators connected to high-voltage transmission grids, neglecting the complexities of the unbalanced low-voltage distribution networks (DNs) that integrate DERs. Consequently, transmission operators cannot effectively assess the impacts of DER dispatch on distribution systems, potentially causing operational inefficiencies and pricing inaccuracies. To address these challenges, this paper develops a novel decentralized optimization approach utilizing reduced DN models, wherein DER market offers are aggregated based on their locations along the primary feeder of the distribution system into networks of virtual power plants (VPPs), thus facilitating coordinated transmission and distribution (T&D) operations. Additionally, a five-stage testbed is proposed to simulate coordinated T&D dispatch and evaluate solution performance across multiple scenarios. Simulation case studies on IEEE 6-, 118-, and 300-bus transmission systems integrated with modified 43-bus distribution networks have demonstrated the effectiveness and efficiency of the proposed framework, which obtains high-quality solutions requiring fewer deviations from scheduled dispatch levels compared to traditional methods, particularly for systems with interconnections between DNs.

A competitive decentralized framework for Volt-VAr optimization of transmission and distribution systems with high penetration of distributed energy resources

Distributed energy resources (DER), such as rooftop solar and combined heat and power (CHP), create a unique opportunity to reduce transmission and distribution network capacity requirements, decrease electrical losses, and potentially improve reliability, resiliency, and other operating metrics. This dissertation examines how DER benefit different stakeholders in the electric power sector: DER owners, ratepayers, utilities, and society. In Chapter 2, we investigate how increasing commercial CHP system peak penetrations may affect net emissions, the distribution network, and total system energy costs. We find that small commercial CHP, due to low and inconsistent heat loads, can increase emissions relative to the bulk grid. We suggest policy options to encourage CHP operation during times of high heat loads. In Chapter 3, we develop metrics based on existing best utility practices that characterize how much solar can reduce peak demand on distribution network feeders. We conclude that solar can act as a capacity resource, but the size of the resource depends on the geographic region. Energy storage or an allowance for occasional overloading within a transformer’s tolerance can increase the capacity resource of solar. Chapter 4 is a value of solar and rate impact study for the Pennsylvania Public Utility Commission (PUC). The Pennsylvania PUC can use it to decide whether the environmental benefits of solar are worth the relatively small rate impact caused by rooftop solar. In Chapter 5, we assess the ability of rooftop solar and storage to reduce peak loads and defer distribution capacity projects in the PECO service territory. We find that targeted placement of solar can increase the total deferral value up to fourfold, but capacity deferral opportunities are rare and large administrative efforts to manage deferral projects, such as markets, are probably not warranted.

Generalized distance-based protection design for DG integrated MV radial distribution networks — Part II: Application to an actual distribution line

Emerging types of software and communication systems that manage distributed energy resources (DERs) such as solar photovoltaic, wind turbines, flywheels, battery storage systems, etc. are termed Distributed Energy Resources Management Systems (DERMS). When properly deployed, their capabilities provide multiple benefits to both, utilities and their customers. DERMS consists of a set of software management tools that allow distribution companies and operators to manage a range of DERs, and offer almost real-time network control. DERMS can help tremendously in integrating, managing, and controlling flexible and intermittent DERs and electric demand. These analyses contribute to keeping the transmission and distribution system in sync with the efficient and reliable balance of supply and demand that should lead to ideally optimization of power flows, electric demand, DERs, and traditional centralized generation. Moreover, in order to handle distributed generation (DG) and to intensify its visibility within power markets, the idea of virtual power plant (VPP) has emerged. Dynamic, automated, and cost-effective management of the distribution system is achieved with DERMS tools that are presented in this paper. Moreover, various hierarchy-levels of DERMS tools co-exist nowadays, such as DER aggregator, VPP, Utility DERMS, and they all can tremendously improve efficiency of Active Distribution Networks (ADN). This paper presents an overview of the current state-of-the-art regarding various DERMS tools, and their capabilities to increase the overall distribution system efficiency.

The AGGREGATE project team successfully developed and validated various modules for outage management. Brief summaries of each module are provided to showcase their strength for outage management and restoration for a distribution system with a high penetration of connected distribution energy resources (DERs).In recent years, inverter-based DERs have been widely deployed in distribution system. A most of behind-the-meter (BTM) solar power generation is not visible to the utility. The data-driven DER and load estimation modules are using machine learning (ML) and artificial intelligence (AI) to manage this issue, which provides an opportunity for distribution system operators (DSOs) to operate systems and make decisions in real-time for a distribution system with a high penetration of DERs deployed. Also, the estimated DER and true load can be further leveraged in network aggregation and cold-load pick up estimation for reducing the computing complexity and providing for fast restoration. After load demand and DER power generations have been estimated, the information will support topology and state estimation(SE). The topology estimation module demonstrated the viability of mixed integer linear programming (MILP) formulation to estimate the most likely operational radial topology and outage sections using power flow measurements, historical/estimated load and DERs data and smart meter ping measurements. Formulation includes continuous (power flow, load and DERs data) and binary measurements (smart meter ping measurements) in a single formulation. Errors in continuous data and binary data are modeled as normal distribution and Bernoulli distribution, respectively. In the future distribution grid, the power injection from controllable DERs will be essential for efficient and resilient grid operation. However, determining the optimal DER injections and restoration actions is dependent on knowledge of the system states. State estimation (SE), already the cornerstone of transmission energy management systems, will become commonplace in distribution management systems as more measurements become available from deployment of automated metering infrastructure (AMI). Observability analysis is the first step in SE, as it determines the sufficiency of the available measurements for accurately estimating the current system states. A new type of pseudo-measurement called a Correlational Measurement (CM) is introduced in this module, to enhance the observability of the system to enable more accurate SE. CMs encapsulate knowledge of correlation between demand patterns for similar classes of loads as well as injection patterns for same-technology renewable DERs. During grid contingency scenarios, DERs have been traditionally disconnected, without any fault ride-through capabilities. However, with new regulations and better technology, it is feasible for these resources to contribute to the grid’s restoration after an adverse event and hence enhance resilience. The controllability module proposes a two-step restoration scheme for the power system restoration process by leveraging additional degrees of freedom in power electronics interfaced DERs for mitigating voltage problems. In a resilience mode without the utility system, the distribution grid relies on DERs to serve critical load. In such a severe event with multiple faults on the distribution feeders, actuation of various protective devices (PDs) divides the distribution system into electrical islands. The undetected actuated PDs due to fault current contributions from DERs can delay the restoration process, thereby reducing the system resilience. The Advanced Outage Management (AOM) and the Advanced Feeder Restoration (AFR) modules developed in this project provide improved system resilience with multiple DERs. AOM identifies the faulted sections and actuated PDs in a distribution system with DERs by incorporating smart meter data. The most credible outage scenario including fault locations, PD actuations, and fault indicator (FI) failures is identified by a set of binary integer linear programming incorporating hypotheses. The AFR module serves to restore a distribution system with available energy resources taking into consideration the availability of utility sources and DERs. By partitioning the system into islands, critical load will be served with the available generation resources within islands based on the solution of a MILP. When the utility systems become available, the optimal path will be determined by a spanning tree search algorithm that reconnects these islands back to substations and restores the remaining load. The transmission and distribution (T&D) co-simulation module was used to validate the effect of a control action performed on the distribution side assets as it propagates to the transmission side. This ensures that the control action performed results in a feasible operating point on both the transmission and the distribution system. In addition to validation, the team used the T&D co-simulation module to demonstrate how distribution system assets can be used to mitigate issues on the transmission system. Specifically, the team demonstrated that appropriate switching operations on the distribution side can alleviate the line overload condition on the transmission side without causing new operational constraint violations.

Enhancing the operation of smart inverters with PMU and data concentrators

Due to the increasing low capacity distributed generators (DGs) installations and penalization of supply disruptions in electrical distribution grid, it is necessary to invest in the distribution protection system. This paper discusses profitability of installation of relays with distance protection function that could protect lines of different voltage levels, lengths and other relevant attributes. The aim is to determine which lines are worth protecting with distance protection and according to that, order of investment by multi-criteria decisionmaking method — analytic hierarchic process (AHP). The first part is an introduction where the circumstances, potential benefits and problems that may arise in distribution grids are presented. This is followed by theory of distance protection and analytic hierarchy process. The final part describes the criteria that should be considered and the way of applying the AHP method with a real example from Croatian distribution grid.

Emission of greenhouse gases and depletion of fossil fuel reserves are two key drivers, which are forcing the mankind to generate the future energy demand from the renewable energy resources. These resources are generally distributed in nature and are directly integrated at distribution levels. Increasing penetration of the distributed energy resources in distribution power networks creates additional operational and control issues. These are mostly regulatory, economical load dispatching, power quality and protection issues.Generally power distribution systems are protected with the help of dedicated over current based protection schemes. But increasing share of distributed energy resources penetration in electric utilities poses a serious threat to the existing protection coordination schemes of the distribution systems. Distributed energy resources connected distribution networks become interconnected in nature and protection coordination schemes, which are designed for unidirectional flow of fault currents become ineffective/non-functional.Therefore, new protection coordination schemes are required for providing the adequate protection coordination for distributed energy resources connected electric power networks. In the available literature, the protection coordination schemes for radial distribution systems and developments in the area of protection coordination are discussed in detail. A thorough review for all these protection coordination schemes for distribution systems with and without distributed energy resources is done in this review article. It includes the analytical and artificial intelligence based techniques application for coordination of protective relays in the distribution systems. The limitations and research gaps in the area of protection coordination schemes are also presented in this review article.The aim of this research paper is to bring all the available research in the area of relay coordination on one platform, so that it will help the emerging researcher to identify the future scope of relay coordination application for distributed energy resources connected distribution systems.

Worldwide there is an increasing need for a more sustainable form of electrical power delivery with a growing share of renewable energy generation. In the distribution and transmission network, large-scale and small-scale wind and solar power plants will be introduced, in proportion to the annual economic growth. The transmission and distribution network will be expanded, focusing on the electricity transport, however, there will also be a need for exchanges with neighboring countries. Alternative solutions are needed in order to support the changes of the future grid. High temperature superconductors are an alternative to conventional conductors, due to their high current density and very low AC loss, and therefore deserve more attention. The purpose of this study is to explore ways to integrate high-temperature superconducting cables in a future network and to compare their favorable technical properties with, e.g., the conventional XLPE cable. The development of 2nd generation high temperature superconducting tapes results in a high tape quality, making it very attractive for use in superconducting power transmission cables. At the same time, the network requirements placed on the grid, based on society needs are changing, such as low magnetic field emissions, reducing space requirements, lower losses, minimizing visual intrusion, etc. Our study shows that superconducting cables compared to conventional cables score better on these societal requirements. From our comparison of three practical low and high temperature superconductors we can conclude that Yttrium Barium Copper Oxide is the most suitable superconductor for use in transmission cables. Our techno-economic analysis shows that superconducting cables become already competitive with conventional cable in the AC transmission, such as XLPE cables. Possible future problems concerning the transport capacity in the power grid where high temperature superconducting cables can offer a solution have been identified. For one promising location, we have formulated the requirements for the design of a high-temperature superconducting cable. Next, we propose two types of cable systems (with cold and warm dielectric). For both types we describe the core, the electrical insulation, the screen, the cryostat, the cooling system, etc. Also for the distribution grid a techno-economic investigation is conducted. To assess the feasibility of the application in distribution grids, we have experimentally demonstrated a reduction of AC conductor losses from 1 W/m to 0.1 W/m. We also carried out an experimental investigation to improve the developed cryostat design for a 6 km long cable connection. Despite these substantial technical improvements our economic study showed that the high-temperature superconducting distribution cable is not yet competitive with the present conventional distribution cable systems except for niche locations where additional advantages e.g. magnetic emission, reduced space usage, power density weighs more heavily. Besides the HVAC grid the Netherlands has HVDC interconnections with neighboring countries and there are initiatives for the use of DC high voltage connections to wind farms further out to sea. In our study, we make reference to a suitable location, where the above mentioned attractive features of the superconducting cable are applicable as well. We advised a modified design of a HTS HVDC cable which enables a possible upgrade of the transmission capacity of the HVDC link at such location. The main results from the investigation are that: • Based on our techno-economic analysis HTS cables offer the most competitive solution in transmission grids. Introduction of such cables will reduce HTS tape price, which in turn will stimulate further applications. • Conceptual designs of competitive HTS AC and DC transmission cables are formulated along with that for HTS AC distribution cable. Novel designs allow for much longer length between cooling stations. • Our experimental research has shown that HTS cable core losses may be reduced by a factor 10 (down to 0.11 W/m/phase at 3 kArms, 77 K, 50 Hz). • Dedicated low friction cable cryostat was developed and successfully tested for 47 meters length. Patented multi-layer thermal insulation improves the cable cryostat heat leak from 1 W/m to 0.1 W/m.

This paper presents a scheme of distance protection for a renewable energy plant in electric power distribution systems. In many developing countries where renewable energy power plants are typically located in rural remote areas, they must be connected to weak power distribution systems inevitably. Although over-current relays are used to protect feeders at substations, fuses are only available elsewhere along feeder lines. To secure the system operation, distance protection is assigned to protect feeders. In this paper, distance relays are placed in the feeder along with over-current relays and fuses. Design of the distance protection of multi-source systems is described. This study considered the system consisting of a renewable energy plant. The power plant was a 6-MW unit of firmed power generation. The test feeder was simplified to be an equivalent four-bus test feeder for relaying purpose. Fault analysis in this paper was performed by using PowerWorld™ software. Obtained fault currents were used to establish protective zones of distance relays. In addition, this paper also compared the result of using distance protection with those of using directional over-current protection. As a result, protection of the power feeder with renewable power plants by using distance relaying can reduce complication in relay setting due to the impedance-based setting of the distance relay.