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The line parameters of power distribution systems stored in the dispatching center may have large errors due to the line aging and system operational dynamics. Such line parameter errors may directly affect the state estimation accuracy, and the advanced management functionalities rely on these parameters. This paper proposes an augmented state estimation method of erroneous distribution line parameters considering the presence of phasor measurement units (PMUs). The augmented state-space models under single and multiple measurement snapshots are established separately by combining the parameter state equation with the state-space model of the distribution network. The augmented state estimation based on the improved adaptive unscented Kalman filter (IAUKF) is developed. The proposed method can effectively perceive the process noise statistical parameter of the erroneous parameters during the estimation to accurately estimate line parameters. The proposed solution is validated through simulation experiments using the IEEE 33-bus system and the numerical results demonstrated its accurate parameter estimation performance.Also, the scalability of the proposed algorithm is demonstrated based on the simulation of the 118-bus system with distributed generators. [ABSTRACT FROM AUTHOR]

The randomness and time variability of power load are the main problems in the load modeling, in which the model error and measurement noise greatly affect the modeling accuracy. In this paper, an adaptive fuzzy logic strong tracking based load modeling method is proposed. The problems of load characteristics and parameter identification of load model are transformed into a real-time tracking of load. The optimal model set is first selected from the initial load model set, and according to the mixing probability, the state estimation and error covariance are mixed as the input of the filter. In order to reduce the model error in the parallel filtering, the strong tracking filter (STF) is constructed based on the orthogonality principle and the filter gain is adjusted by introducing a time-varying fading factor. The adaptive fuzzy logic strong tracking filter is constructed by combining the fuzzy logic with the STF to adjust the covariance matrix of the STF according to the change of measurement noise. Moreover, the weights of each sub model are updated in real time by the parallel filtering, and the sub models are fused to get a comprehensive load model which can reflect the actual load characteristics. The effectiveness of the method is verified by the simulation of IEEE 39-bus system. This method can establish an accurate load model and has good robustness. [ABSTRACT FROM AUTHOR]

False data injection (FDI), could cause severe uneconomic system operation and even large blackout, which is further compounded by the increasingly integrated fluctuating renewable generation. As a commonly conducted type of FDI, load redistribution (LR) attack is judiciously manipulated by attackers to alter the load measurement on power buses and affect the normal operation of power systems. In particular, LR attacks have been proved to easily bypass the detection of state estimation. This paper presents a novel distributionally robust optimization (DRO) for operating transmission systems against cyber-attacks while considering the uncertainty of renewable generation. The FDI imposed by an adversary aims to maximally alter system parameters and mislead system operations while the proposed optimization method is used to reduce the risks caused by FDI. Unlike the worst-case-oriented robust optimization, DRO neglects the extremely low-probability case and thus weakens the conservatism, resulting in more economical operation schemes. To obtain computational tractability, a semidefinite programming problem is reformulated and a constraint generation algorithm is utilized to efficiently solve the original problem in a hierarchical master and sub-problem framework. The proposed method can produce more secure and economic operation for the system of rich renewable under LR attacks, reducing load shedding and operation cost to benefit end customers, network operators, and renewable generation. [ABSTRACT FROM AUTHOR]

Real-time monitoring is a key tool for several automated features in distribution system. However, due to the limited number of real-time measurements, distribution system monitoring generally relies on load modeling procedures. This paper presents field results for a real-time monitoring tool that was implemented on a Brazilian distribution utility to provide load values for service restoration software. The implemented tool comprises two steps. The first step consists of preprocessing routines that provide the required information for a real-time load estimator that is executed in the second step. The field results provide evidence of the practical viability of the implemented real-time monitoring tool, demonstrating the tool overcomes some usual limitations of real-time load estimation procedures. More specifically, the implemented tool is able to handle multiple and different types of real-time measurements, treat real-time measurements on the feeder and not only in the head of the feeder, handle obviously bad data, and to satisfy the performance requirements on practically sized distribution systems. Besides proposing and confirming a real-time monitoring tool on a real distribution system, this paper shares valuable utility experience on providing new insights and the challenges faced for real-time monitoring projects. [ABSTRACT FROM PUBLISHER]

With the increased interest in controlling and managing voltage unbalance (VU), network operators are now increasingly being motivated to obtain the state of their networks with greater details. Distribution system state estimation (DSSE) is a prominent tool that enables network operators to estimate the level, location, and related impacts of VU. DSSE techniques developed to date which use the polynomial or exponential load models are deficient in recognizing VU attenuation associated with three-phase induction motors (IMs) that are directly connected to the ac network. Adoption of adequate three-phase models of IMs, which are used in full unbalanced load flow, into the existing DSSE techniques is not feasible due to several factors including requirement of extensive data, additional computational efforts, and major constraints related to incorporating the necessary modifications. As a solution, this paper proposes a novel formulation for postprocessing the results of current DSSE techniques to reflect the aforementioned behavior of IMs. Simulations are carried out using the IEEE 13 bus distribution network for a range of scenarios to verify the developed methodology. The work presented in relation to VU attenuation in interconnected networks also complements the existing treatise in IEC documentation that only deals with radial networks. [ABSTRACT FROM AUTHOR]

Dynamic rating monitoring is a solution to face challenges in both the operation and the planning of power systems. With thermal monitoring, dynamic overloads of transformers are allowed; however, the thermal model used to predict hot-spot must be capable of ensuring the assessment of insulation life expectancy. Hence, this paper presents an online algorithm to estimate and predict transformers’ rating in order to assess the overload capability during short and long times. The overload factors are computed using estimations of top-oil temperature. The main characteristic of this proposal is that the environmental cooling conditions are considered by the fitting of the parameters of a simple equivalent thermal circuit using an extended Kalman filter during the transformer operation. To validate the implementation of the algorithm, the information provided by typical transformer rating monitoring systems is used. Thus, the performance and effectiveness of the algorithm are verified using field measurement data during the normal operation of two power transformers. [ABSTRACT FROM AUTHOR]

The introduction of the microprocessor-based numerical relay in the 1980s resulted in multifunctional, multidimensional, communications-enabled complex protection systems for zone and system protection. The increasing capabilities of this technology created new unintended challenges: 1) complexity has increased and selecting coordinated settings is a challenge leading to occasional miscoordination; 2) protection functions still rely on a small number of measurements (typically three voltages and three currents) limiting the ability of protection functions to dependably identify the type of fault conditions; and 3) present approaches are incapable of dealing with hidden failures in the protection system. Statistically, 10% of protection operations are misoperations. This paper presents a new approach to protection that promises to eliminate the majority of the problems that lead to misoperations. The approach is described, demonstrated in the laboratory, compared to traditional protection functions and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described. This paper also discusses the planned field testing of the approach. [ABSTRACT FROM AUTHOR]

This paper proposes an effective scheme for real-time operation and protection of microgrids based on the distributed dynamic state estimation (DDSE) that is applied to a single renewable distributed energy resource (DER) or other components. First, the DDSE can be used for setting-less component protection that applies dynamic state estimation on a component under protection with real-time measurements and dynamic models of the component. Based on the results, the well-known chi-square test yields the confidence level that quantifies the goodness of fit of models to measurements, indicating the health status of the component. With this approach, renewable DERs in microgrids can be protected on an autonomous and adaptive basis. Meanwhile, the estimated state variables of each component are converted to phasor data with time tags, and then collected to the distributed energy resources management (DERMS) of microgrids. These aggregated phasor data that are once filtered by the DDSE are input to the static state estimation in the DERMS along with unfiltered data sent from conventional meters, relays, and digital fault recorders, ultimately generating real-time operating conditions of microgrids. This paper also provides numerical simulations for comparing the DDSE-based approach with the conventional centralized state estimation in terms of data accuracy and computational speeds. [ABSTRACT FROM AUTHOR]

In this paper, we present a new approach for solving the problem of power quality monitors (PQMs) optimal allocation, for the monitoring of short-duration voltage variations caused by a fault condition in a power grid system. The problem is treated in a multiobjective perspective with two optimal criteria: minimization of the number of PQMs and maximization of the number of identified faults. Non-identification of an event can occur as a result of symmetry conditions in the network, i.e., in cases where two or more faults generate the same signals in some buses, which leads to ambiguity in the monitoring results. Symmetry increases the complexity of both the problem formulation and solution. The problem is described as a multiobjective discrete optimization problem and is solved by the algorithm for bicriteria discrete optimization within reasonable computational time. That approach was tested in power grids of different characteristics and sizes. The results demonstrate the proposed methodology applicability for solving the problem in real-size networks. [ABSTRACT FROM AUTHOR]

This paper proposes a methodology for transient state estimation in power systems. The proposed methodology is formulated using approximation methods for derivatives to relate the state variables to measurements. It does not require knowledge of the steady state to establish the predisturbance operation conditions. The method uses an optimal monitoring system based on topological analysis to obtain full observability. A saving index is introduced to analyze the effectiveness of the instrumentation used. The adverse effect of noisy measurements in the estimation process is mitigated by using an infinite impulse response filter. A transient index is introduced to estimate the fault location. The transient state estimation is assessed using two test systems. The results are validated through direct comparison against those obtained by simulation using SimPowerSystems toolbox of Simulink. With the proposed methodology, the transient state estimation can be obtained with an important saving in the implementation of the measuring system and with considerably less computational effort. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Smart Grids employ intelligent control applications that require high quality data: fast, secure, and error free. Several researchers have focused on providing techniques for low latency and secured data links for these applications. Bad data detection is however generally provided only at the central level due to limitations in legacy technologies employed in many substations. With the introduction of IEC61850 data sharing within the substation becomes more flexible and transparent allowing more sophisticated management of data quality. Hence, this paper proposes a substation level bad data detection algorithm to facilitate also these types of requirements from applications. The algorithm is based on automatically detecting the substation topology by parsing standard substation description files and online state of circuit breakers and disconnectors. By applying linear weighted least square based state estimation algorithm, bad data from failing current transformers (CT) can be detected. By conducting the verification of different types of bad data, the results show the output of bad data detection algorithm provides higher accuracy than output from both measurement and protective CT in both static and faulty situations. [ABSTRACT FROM PUBLISHER]

This paper presents a new technique for voltage sag state estimation. The proposed method is based on estimating the number of voltage sags occurring at nonmonitored buses from the number of sags recorded at a limited number of monitored buses. This problem, contrary to the traditional state estimation where redundant measurements are available, is formulated as an underdetermined system of equations. In this paper, linear integer programming techniques are employed to solve this estimation problem. The performance of the proposed method is tested by means of several case studies applied in the IEEE 24-bus Reliability Test System (RTS) and in the IEEE 118-bus Test System. [ABSTRACT FROM AUTHOR]

Voltage dip is a frequently occurring power-quality problem that electricity consumers face. Knowledge of the source and magnitude of the voltage dip is desirable; however, complete monitoring of the power system is prohibitive. State estimation for both fundamental and harmonic frequencies was presented previously. Its ability to utilize limited measurements for system-wide estimation has proven to be very effective. In this paper, the technique is extended further to estimate power system transients. Transient state estimation (TSE) provides an effective and systematic approach in locating and identifying remote fault sources, thus allowing the problem to be addressed more efficiently. The proposed approach formulates the system using state-space theory and results in a system of first-order differential equations which are used to form the measurement system. The estimation is the simultaneous solution of the measurement system equations based on a time sequence of snapshots of the system measurements. Additional measurement information utilizes the voltage and current history measurements where they are approximated using backward Euler integration formula, are also supplied to the TSE algorithm. To evaluate the performance of the proposed TSE, transients caused by a sudden lost of a system load have been simulated on the test system. This paper provides a new methodology to estimate a complete transient profile of a power system. [ABSTRACT FROM AUTHOR]

The harmonic state-estimation (HSE) method appears to be effective but its applicability has yet been fully verified using actual data in power systems. Particularly in Japan, there has been no verification of the applicability of the method in actual power systems. In this paper, for Japanese field data synchronized with a Global Positioning System (GPS) clock, a practical method for power system harmonic analysis is proposed, which is based on HSE. In the proposed method, in order to improve the precision of HSE, uncertain parameters R, X, and Y of the transmission lines are determined from measured fundamental data, and bad measured harmonic data excluded systematically. It is also possible to estimate the error of each measurement instrument by using HSE. It is confirmed that by using only partial and selected measurement data synchronized with a GPS clock, the entire harmonic distribution of the actual power system has been obtained effectively. In this paper, field-test results of the HSE on an actual Japanese power system are shown. Furthermore, an example of harmonic analysis based on HSE in the actual power system is presented, which is prediction of harmonic voltage distribution after a change of the actual power system configuration. [ABSTRACT FROM PUBLISHER]

Phasor measurement units (PMUs) are becoming an important component in the power grid. The PMUs provide time-synchronized measurements of multiple remote measurement points, enabling more accurate and real-time monitoring of the system state. Heuristically, it is difficult to tell how the placement of a PMU at a specific location in the power system would affect the state estimation error, not to say the effect of the PMU synchronization and measurement accuracy. In this paper, we derive the posterior Cramér-Rao bound (PCRB) on the state estimation error based on a measurement model which considers the phase-angle mismatch from PMU measurements. We then propose a PMU placement strategy using the derived PCRB. The greedy algorithm is used to solve the optimization problem. The results are then compared with other heuristics, with the optimal solution through an exhaustive search (for small systems), and with a lower bound on the optimal placement obtained through convex relaxation. For some design criteria, the objective functions are submodular, which guarantees a performance bound on the greedy solution. For other design criteria where the objective functions are not submodular, numerical examples demonstrate the effectiveness of the greedy algorithms. [ABSTRACT FROM AUTHOR]

Voltage unbalance is a costly and potentially damaging phenomenon. It affects both distribution network operators (DNOs) and customers. As part of a move toward greater network visibility, DNOs are increasingly motivated to monitor their networks in finer detail using an increasingly diverse range of monitoring devices. If the information from monitoring devices can be collated intelligently, the impact of unbalance and other power-quality issues can be accurately estimated throughout the network. In this paper, a new methodology is presented which utilizes distribution system state estimation (DSSE) to estimate the level, location, and impact of voltage unbalance on a real distribution network. The developed methodology is novel, pulling together and advancing existing research on DSSE and unbalance. The methodology is validated using data from a real U.K. distribution network with significant unbalance. The methodology is shown to be capable of statistically estimating the level, location, and effects of unbalance within the network, even when some areas of the network are unobservable. [ABSTRACT FROM AUTHOR]

It is well known that environmental loads, e.g., wind and ice, acting on power transmission lines are highly uncertain, as are the structural strengths of the towers supporting the lines. The design of such systems must take uncertainty into account in order to achieve acceptable reliability at a reasonable cost. The paper presents a simulation-based methodology for the optimal design of a transmission line which considers uncertainties in both environmental loads and structural resistance. The methodology is developed and illustrated for the simple problem of determining the optimal span length required for designing against tower failure. Wind, ice, and tower resistances are simulated over the extent of the transmission line and over the design life of the transmission system. Total expected system cost, along with the estimated probability of lifetime failure, are produced for a range of possible span lengths, allowing an informed decision regarding the optimum span length for the tower strength limit state. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to estimate harmonic distortions in a power system, based on measurements of a limited number of given sites. The algorithm utilizes evolutionary strategies (ES), a development branch of evolutionary algorithms. The main advantage in using such a technique relies upon its modeling facilities as well as its potential to solve fairly complex problems. The problem-solving algorithm herein proposed makes use of data from various power-quality (PQ) meters, which can either be synchronized by high technology global positioning system devices or by using information from a fundamental frequency load flow. This second approach makes the overall PQ monitoring system much less costly. The algorithm is applied to an IEEE test network, for which sensitivity analysis is performed to determine how the parameters of the ES can be selected so that the algorithm performs in an effective way. Case studies show fairly promising results and the robustness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract-Due to an increase of power-electronic equipment installation and other harmonic sources, the identification and estimation of harmonic loads are of concern in electric power transmission and distribution systems. Conventional harmonic state estimation requires a redundant number of expensive harmonic measurements. In this paper, we explore the use of a statistical signalprocessing technique, known as independent component analysis (ICA) for harmonic source identification and estimation. If the harmonic currents are statistically independent, ICA is able to estimate the currents using a limited number of harmonic voltage measurements and without any knowledge of the system admittances or topology. The results are presented with computer simulations for the modified IEEE 30-bus test system. [ABSTRACT FROM AUTHOR]

In a deregulated electricity industry, new concerns have emerged regarding the quality of the power supply as companies tend to focus on their own objectives and interests. One main concern regarding power-supply quality is voltage fluctuation. Voltage fluctuations are defined as repetitive or random variations in the magnitude of the supply voltage. This paper addresses a method for monitoring the voltage flicker using state estimation (FSE). A test system is used to characterize the new algorithm in which parameter inaccuracies have been considered. The new algorithm can be used by operators as well as distribution companies to monitor the flicker severity throughout the network. [ABSTRACT FROM AUTHOR]

Active management of complex distribution networks with distributed generation requires state estimation. As complete supervisory control and data acquisition systems are seldom available on 11-kV or lower voltage distribution networks, real-time measurements at remote points on 11-kV distribution networks are expensive. Therefore, the economical selection of a communication system for active management of distribution networks with distributed generation becomes an important issue. This paper presents the investigations into a leased communication system made of public-switched communication network channels for a distribution network state estimation application. It analyzes the effects of a different number of primary channels for real-time measurements on the distribution network state estimation accuracy. The leased communication system availability performance has also been analyzed and used to identify a number of reserve channels required to improve the leased system availability. The overall cost for improving the leased communication system availability has been calculated and compared with both a fiber-optic communication system and a power-line carrier communication system. The results show that the leased communication system is able to provide the lowest overall cost performance for the distribution network state estimation application. [ABSTRACT FROM AUTHOR]

This paper presents a new method for an optimal measurement placement of phasor measurement units (PMUs) for power system state estimation. The proposed method considers two types of contingency conditions (i.e., single measurement loss and single-branch outage) in order to obtain a reliable measurement system. First, the minimum condition number of the normalized measurement matrix is used as the criteria in conjunction with the sequential elimination approach to obtain a completely determined condition. Next, a sequential addition approach is used to search for necessary candidates for single measurement loss and single-branch outage conditions. These redundant measurements are optimized by binary integer programming. Finally, in order to minimize the number of PMU placement sites, a heuristic technique to rearrange measurement positions is also proposed. Numerical results on the IEEE test systems are demonstrated. [ABSTRACT FROM AUTHOR]

The effectiveness of harmonic state estimation (HSE) in identifying the location and magnitude of harmonic sources is largely dependent on the accuracy of the measurements. Measurement errors (or bad data) can be classified into two groups; measurement noise and gross error. This paper uses a statistical approach (cumulative probability density functions) obtained from five thousand Monte Carlos runs to investigate the impact of measurement noise and gross errors in harmonic state estimation. The Lower South Island of the New Zealand system is used as the test system and the results are probability curves containing the statistics of the estimation error. The effect of additional measurements on an over-determined system to filter noise is also discussed. [ABSTRACT FROM PUBLISHER]