Customer Outages Research Articles

High-resolution, open-source modeling of inland flooding impacts on the North Carolina bulk electric power grid

Although damages to local distribution systems from wind and fallen trees are typically responsible for the largest fraction of electricity outages during hurricanes, outages caused by flooding of electrical substations pose a unique risk. Electrical substations are a key component of electric power systems, and in some areas, the loss of a single substation can cause widespread power outages. Before repairing damaged substations, utilities must first allow floodwaters to recede, potentially leaving some customers without power for weeks following storms. As economic losses from flooding continue to increase in the U.S., there has been increasing attention paid to the potential impacts of flooding on power systems. Yet, this attention has mostly been limited to geospatial risk assessments that identify what assets are in the path of flooding. Here, we present the first major attempt to understand how flooding from hurricanes and other extreme precipitation events affects the dynamic behavior of power networks, including losses of demand and generation, and altered power flows through transmission lines. We use North Carolina, hit by major hurricanes in three of the past seven years, as a test case. Using open-source data of grid infrastructure, we develop a high-resolution direct current optimal power flow model that simulates electricity production and generators and power flows through a network consisting of 662 nodes and 790 lines. We then simulate grid operations during the historical (2018) storm Hurricane Florence. Time series of flooding depth at a discrete set of ‘high water’ mark points from the storm are used to spatially interpolate flooding depth across the footprint area of the storms on an hourly basis. Outages of substations and solar farms due to flooding are translated to location-specific losses of demand and solar power production throughout the network. We perform sensitivity analysis to explore grid impacts as a function of the height of sensitive equipment at substations. Results shed light on the potential for localized impacts from flooding to have wider impacts throughout the grid (including in areas not affected by flooding), with performance tracked in terms of transmission line flows/congestion, generation outputs, and customer outages.

Roadmap to modernization of line protection in active distribution systems

The nature of distribution systems is changing from passive to active networks due to the integration of Distributed Energy Resources, especially Inverter-Based Distributed Generation (IBDG). This change presents challenges for existing fuse-based unidirectional protection schemes, as active networks experience bidirectional flow of power and small fault current contribution from IBDGs. Such fault behavior can impact the protection scheme’s sensitivity and selectivity, compromising the reliability of active distribution networks and leading to customer outages due to improper fault isolation. The problem is exacerbated in networks that allow the islanded mode of operation. Upgrading the entire protection system to microprocessor-based relays is expensive. Instead, this work proposes a planning strategy to optimally upgrade protective devices. The proposed framework is able to incorporate IBDG integration plans, distribution system reliability targets, protection requirements, and economic viability throughout the planning horizon. The obtained strategy determines the optimal number, location, and deployment time of protective devices in consideration of network characteristics. The developed optimization model is formulated as a Mixed-Integer Linear Programming problem. The results verify the proposed framework’s ability to economically upgrade the protection scheme while enhancing the reliability of the active distribution network with IBDGs.

An Enhanced MILP Model for Multistage Reliability-Constrained Distribution Network Expansion Planning

Reliability is an essential factor in distribution networkt expansion planning. However, standard distribution reliability assessment techniques rely on quantifying the impact of a pre-specified set of events on service continuity through the simulation of component outages, one at a time. Due to such a simulation-based nature, the incorporation of reliability into distribution network expansion planning has customarily required the application of heuristic and metaheuristic approaches. Recently, alternative mixed-integer linear programming (MILP) models have been proposed for distribution network expansion planning considering reliability. Nonetheless, such models suffer from either low computational efficiency or over-simplification. To overcome these shortcomings, this paper proposes an enhanced MILP model for multistage reliability-constrained distribution network expansion planning. Leveraging an efficient, yet accurate reliability evaluation model, proposing a customized technique for effectively imposing radial operation, as well as utilizing pragmatic measures to model reliability-related costs are the salient features of this work. In this respect, practical reliability-related costs are considered based on reliability incentive schemes and the revenue lost due to undelivered energy during customer outages. The proposed planning approach is tested on four networks with 24, 54, 86, and 138 nodes to illustrate its efficiency and applicability.

Optimalisasi Load Break Switch Motorized Menggunakan Fungsi Sectionalizer Berbasis Scada pada Penyulang Bacan ULP Pulung Kencana

The medium voltage network of bacan feeders was an air line power network and had a very high potential to experience disruptions impacted on customer outages. The bacan feeder network was divided into sections uisng breaker equipment (Recloser/LSBM) in order to narrow down the area of blackout when a disturbance occurs. The work function of the breaker equipment was not yet optimal, so it can have an impact on the length of time the customer goes out when there was a network disturbance. From the simulation of the existing feeder conditions, the ENS (Energy Not Supplied) results were really high and the duration of the shutdown was every long so we optimize the breaker equipment (LBSM) by resetting the sectionalizer and telesignaling SCADA (Supervisory Control And Data Acquisition) and RTU (Remote Terminal Unit) on LBSM that has not been intergrated with SCADA. Based on the results of the analysis, evaluation and simulation, after the optimization of the SCADA-based sectionalizer function had been applied to the LBSM equipment, the ENS value and the feeder shutdown duration function due to the disturbance of the bacan feeder network could be significantly reduced

A Practical Approach to Optimising Distribution Transformer Tap Settings

This paper proposes a method of determining the optimal tap settings for no-load distribution transformers with tap-changing capabilities that is practical to apply in real distribution networks. The risk of low voltage distribution networks violating voltage constraints is impacted by the increasing uptake of distributed energy resources and embedded generation. Some of this risk can be alleviated by suitably setting no-load transformer tap settings, however, modifying these taps requires customer outages and must be infrequent. Hence, loading over the entire year must be considered to account for seasonal variations when setting these taps optimally. These settings are determined using evolution strategy optimisation based on an average loading case. Monte Carlo simulations are used to calculate the probability that the terminal voltages on the distribution transformer secondary terminals violate the network voltage limits when the optimal set of taps for the average case is applied over a whole year. This algorithm was tested on several cases of a real distribution feeder of varying complexity, and produces a sufficiently-optimal set of taps without significant computation time.

A Spatial Analytics Framework to Investigate Electric Power-Failure Events and Their Causes

The U.S. electric-power infrastructure urgently needs renovation. Recent major power outages in California, New York, Texas, and Florida have highlighted U.S. electric-power unreliability. The media have discussed the U.S. aging power infrastructure and the Public Utilities Commission has demanded a comprehensive review of the causes of recent power outages. This paper explores geographic information systems (GIS) and a spatially enhanced predictive power-outage model to address: How may spatial analytics enhance our understanding of power outages? To answer this research question, we developed a spatial analysis framework that utilities can use to investigate power-failure events and their causes. Analysis revealed areas of statistically significant power outages due to multiple causes. This study’s GIS model can help to advance smart-grid reliability by, for example, elucidating power-failure root causes, defining a data-responsive blackout solution, or implementing a continuous monitoring and management solution. We unveil a novel use of spatial analytics to enhance power-outage understanding. Future work may involve connecting to virtually any type of streaming-data feed and transforming GIS applications into frontline decision applications, showing power-outage incidents as they occur. GIS can be a major resource for electronic-inspection systems to lower the duration of customer outages, improve crew response time, as well as reduce labor and overtime costs.

Development of a Typhoon Power Outage Model in Guangdong, China

In this study, typhoon power outage models were developed to predict the number of customer outages and damaged poles in Xuwen, Guangdong, China using data from three typhoons: Rammasun, Kalmaegi and Mujigae. Our hold-out validation demonstrates that these models can accurately estimate the number of customer outages and damaged poles from typhoons. The mean relative error is 5.1% in the customer outage model and 9.6% in the pole damage model. This study has two key improvements over previous work. First, our models provide more accurate predictions through leveraging a variety of static and dynamic variables that characterize the typhoon hazard and local environmental conditions. Maximum gust wind speed, elevation, land cover and duration of strong winds are the four most important variables for both the customer and pole models. Second, we demonstrate that it is possible to provide skillful predictions of power outages at 1-km resolution. This is a significantly higher spatial resolution than past tropical cyclone power outage models. The models will be used to support improved decision making. The operational power outage forecasts will be used by the electrical utility for pre-positioning crews and materials and to notify customers who are likely to lose power.

Identifying Recommended Funding Levels of Power Grid Resilience Programs

How does a public electric utility company optimize its capital budget for grid reliability? We illustrate an economically optimal way to allocate funding these efforts using circuit-level data from Eversource Energy to quantify the benefits to tree trimming treatments over the period of 2013-2017. A real options framework allows us to quantify in dollar terms the uncertain benefits in terms of customer outages avoided relative to known costs of treatment. We find that the less costly Standard Maintenance Trimming (SMT) is economically effective for all circuit types observed in Eversource's CT grid, while the more extensive Enhanced Tree Trimming (ETT) is effective on dense circuits only. Compared to this model, a traditional discounted cash flow model leads to underinvestment in grid resilience and ignores both uncertainty in estimates and the ability to change policy based on its efficacy.

National platform for information on customer interruptions and outages in Denmark

National platform for information on customer interruptions and outages in Denmark

A Novel Method Based on Teaching-Learning-Based Optimization for Recloser Placement with Load Model Consideration in Distribution System

<em>This paper proposed a novel technique based on teaching-learning-based optimization (TLBO) algorithm in order to find optimal placement of reclosers in the distribution networks which is applied to improve reliability. Reclosers use to eliminate transient faults, faults isolation, network management and enhance reliability to reduce customer outages. According to recloser role in network reliability, the cost for the installation and maintenance must be sustained by distribution companies. Therefore, selecting sufficient number and suitable location for reclosers are important issue. In this paper, the proposed objective function for optimal recloser number and placement has been formulated to improve three reliability indices which consists of three terms; i.e. System Average Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI) and Average Energy Not Supplied (AENS). Besides the load model effectiveness has been considered to the simulation. To verify the efficiency of proposed method, it has been conducted to IEEE 69-bus radial distribution system. The obtained simulation results demonstrate the reliability improvement.</em>

Pareto Optimal Reconfiguration of Power Distribution Systems with Load Uncertainty and Recloser Placement Simultaneousely Using a Genetic Algorithm Based on NSGA-II

<em><span>Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important measures which can improve the operational performance of a distribution system. Besides, reclosers use to eliminate transient faults, faults isolation, network management and enhance reliability to reduce customer outages. For load uncertainty a new method based on probabilistic interval arithmetic approach is used to incorporate uncertainty in load demand that can forecast reasonably accurate operational conditions of radial system distribution (RDS) with better computational efficiency.<strong> </strong>In this paper, the optimization process is performed by considering power loss reduction along with reliability index as objective functions. Simulation results on radial 33 buses test system indicates that simultaneous optimization of these two issues has significant impact on system performance.</span></em>

Off-line tracking of series parameters in distribution systems using AMI data

In the past, electric distribution systems have lacked measurement points, and equipment is often operated to its failure point, resulting in customer outages. The widespread deployment of sensors improves distribution level observability. This paper presents an off-line parameter tracking procedure that leverages the increased deployment of distribution level measurement devices to estimate changes in impedance parameters over time. Parameter tracking enables the discovery of non-diurnal and non-seasonal changes, which can be flagged for investigation. The presented method uses an unbalanced distribution-system state-estimator and a measurement-residual based parameter-estimation procedure. Measurement residuals from multiple measurement snapshots are combined to increase effective local redundancy and improve robustness to measurement noise. The input data used in the experiments consists of data from devices on the primary distribution system and from customer meters, via an AMI system. Results of simulations on the IEEE 13-Node Test Feeder with 307 measurements and 246 parameters are presented to illustrate the proposed approach applied to changes in series impedance parameters. The proposed approach can detect a 5% change in series resistance elements with 2% measurement error using less than 1 day of measurement snapshots for a single estimate.

Efficient Resilience Assessment Framework for Electric Power Systems Affected by Hurricane Events

AbstractEnsuring electric power system resilience against natural and anthropogenic hazards is vital for public health, economy, security, and well-being across modern societies. This paper presents a resilience assessment framework that focuses on computationally efficient algorithms for quantifying the response of electric power systems to hurricane events, while demonstrating its applicability to large real systems by spanning hazards, structural and system responses, and restoration processes. The study models the transmission system responses as a Bayesian network to represent probabilistic dependencies in an intuitive and tractable manner. It propagates hurricane-induced failures throughout the system to service customers while efficiently considering the physics and constraints of power flow. The framework computes customer outages in distributed 1-km2 blocks connected by radial distribution feeders across the entire system, and simulates system restoration according to resource mobilization practi...

Impact of Smart Grids and Green Power Generation on Distribution Systems

A significant amount of green power is being installed at the distribution level through the installation of green power generation facilities in the U.S. and Canada. This paper discusses green-power-generating sources (of 10 MW or less), which are connected to the utility system at the distribution level, and their impact on the distribution system. This paper also discusses the impact of smart grid and whether this new technology can solve some of the issues raised in this paper. Distribution circuits are designed to supply radial loads. Therefore, the introduction of green generation could mean redistribution of fault and load currents on the feeder circuit, overvoltage, and ferroresonance, plus a possible loss of protection system coordination-all of which can result in customer outages. This paper discusses these issues which are generally not well understood by many distribution protection engineers and can adversely affect distribution system reliability.

Optimized Allocation of Control and Protective Devices in Electric Distribution Systems

Optimized allocation and/or reallocation of control and protective devices in distribution networks allow for better operation and improved system reliability indices. Control devices (used to reconfigure the feeders) are allocated in distribution networks to obtain an optimal operation strategy in order to facilitate power supply restoration in case of a contingency. Protective devices (used to isolate faults) are allocated in distribution systems to improve the reliability and continuity of power supply. Protective devices significantly reduce the impacts of faults in terms of customer outages and the time needed for fault location and system restoration. This work presents a mixed-integer non-linear programming model for the sectionalizing switches and protective devices allocation and/or reallocation problem. The constraints considered for the problem reflect technical and economical limitations, such as in-series protective devices coordination, number of available equipment, importance of the analyzed feeder, circuit topology, quality of power supply, and physical limitations of the system. A dedicated reactive tabu search algorithm is proposed for solving this problem. Results and optimized strategies for allocating or reallocating protection devices and switches considering a real-life network restoration are presented.

Optimised placement of control and protective devices in electric distribution systems through reactive tabu search algorithm

Optimised placement of control and protective devices in distribution networks allows for a better operation and improvement of the reliability indices of the system. Control devices (used to reconfigure the feeders) are placed in distribution networks to obtain an optimal operation strategy to facilitate power supply restoration in the case of a contingency. Protective devices (used to isolate faults) are placed in distribution systems to improve the reliability and continuity of the power supply, significantly reducing the impacts that a fault can have in terms of customer outages, and the time needed for fault location and system restoration. This paper presents a novel technique to optimally place both control and protective devices in the same optimisation process on radial distribution feeders. The problem is modelled through mixed integer non-linear programming (MINLP) with real and binary variables. The reactive tabu search algorithm (RTS) is proposed to solve this problem. Results and optimised strategies for placing control and protective devices considering a practical feeder are presented.

A census of Tandem system availability between 1985 and 1990

A census of customer outages reported to Tandem showing a clear improvement in the reliability of hardware and maintenance has been taken. It indicates that software is now the major source of reported outages (62%), followed by system operations (15%). This is a dramatic shift from the statistics for 1985. Even after discounting systematic underreporting of operations and environmental outages, the conclusion is clear: hardware faults and hardware maintenance are no longer a major source of outages. As the other components of the system become increasingly reliable, software necessarily becomes the dominant cause of outages. Achieving higher availability requires improvement in software quality and software fault tolerance, simpler operations, and tolerance of operational faults.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An Approach to Microwave Relaying and System Design

1. The concept of fully reliable and secure communication facilities, completely separate from the power system, provides a new approach to problems of system design, relay protection, and system operations. 2. Initial tests demonstrate that microwave equipment can provide these communication facilities and that its use for protective relaying communications is practical. 3. Protective relaying by the use of microwave presents the following advantages: (a). No power system components or connections are used, with the following results: (1) The number of high-voltage components are reduced thus minimizing equipment failures which might cause customer outages. (2) Component failures need not cause circuit outages; stand-by equipment is practical and economical. (3) Maintenance of the equipment can be done without circuit outages. (4) Personnel and system hazards are minimized because of the reduced high-voltage switching for construction and maintenance needs. (5) The problem of additional space required for 1,200-ampere traps and for coupling devices as in carrier-relaying installations is avoided. (b). A new degree of freedom is available for integrating older parts of the system into new system requirements. (c) Multiterminal line-relaying problems are minimized and satisfactory system performance can be realized with microwave relaying from many system configurations formerly considered unsatisfactory because of relaying limitations. 4. The zone-comparison method can readily be applied to available types of relays and even existing relay installations. The control circuitry required is relatively simple.