Remedial Action Schemes Research Articles

A rapid PMU-based load composition and PMU estimation method

Advanced protection and operation of power systems, especially microgrids, requires rapid detection and estimation of system states. Microgrids, however, are a challenge due to the high variability of distributed generation and modern load profiles. Setting of relays and establishing Remedial Action Schemes on these systems requires rapid detection and state estimation and modeling of complex loads. This work demonstrates the design and operation of a high-speed method for estimating states and load composition across a 286-bus campus test-bed utilizing only a few PMUs. The method is based on training data that is analyzed offline via Singular Value Decomposition to determine clustering vectors that can be utilized for state estimation in real-time. This is combined with a priori bus studies to estimate load composition in terms of residential, industrial, and commercial in real-time. A case-study using the Oregon State University campus grid is presented, and it is shown that the estimation method is accurate (to within 1% in the test shown) while requiring less than 0.2ms computation time.

Special Protection Schemes: A Survey and Vision for the Future

Any power system network is subjected to disturbances at any time and place. It is considered as one of the most stochastic system ever seen by the human beings. To enhance the power system reliability, System Protection Scheme (SPS) is an effective tool for utilizing the power grid during rare contingencies. This method is often employed as secondary protection schemes. SPS is also termed as Special Protection Scheme. SPS is referred with different names by different users such as IEEE as System Integrity Protection Scheme (SIPS), Bonneville Power Administration (BPA) as Remedial Action Scheme (RAS) and WECC and others as SPS. In India, only in late 90s, the concept of SPS was introduced to solve the above problem. In Indian power grid different SPS has been designed and implemented successfully. This paper presents a complete knowledge, need , general structure, characteristics and a brief description of the major SPS employed in various Indian Power grids. Post - commissioning performance of these SPS has also been analyzed briefly. Finally, highlights of major issues involved with the employment of SPS in the Indian scenario.

Role of Statistical and Machine Learning Methods in Special Protection Scheme Logic Design and Failure Assessment

With tremendous growth in variable renewable generation and uncertainties in power system operations, there has been lot of installations of special protection schemes in many parts of the world. A special protection scheme, also termed a remedial action scheme, is the high-end last line of defense mechanism to relieve the system from catastrophic consequences under highly stressed conditions. This article delineates the special protection scheme logic design process and, with the help of a Nordic grid case study, proposes a new paradigm of special protection scheme failure assessment and logic design process, namely the “system-view” framework. In this context, the article also demonstrates the application of decision tree-based methods to derive special protection scheme operational logic and provides a pathway to use efficient statistical sampling techniques for implementing the system-view special protection scheme failure assessment method, thereby advancing the logic redesign process.

Event‐based remedial action scheme against super‐component contingencies to avert frequency and voltage instabilities

Frequency instability, voltage instability or a combination of both have been the cause of several power system breakdowns throughout the world in the recent decades. Occurrence of a super-component contingency (SCC) that refers to multiple and simultaneous outages of grid facilities like a power plant or substation may lead to blackout if no remedial action schemes (RAS) are implemented. This study proposes a new event-based RAS to overcome the frequency and voltage instabilities caused by SCCs through optimal load shedding. To do this, a new multi-objective framework is presented simultaneously optimising the competing objective functions of long-term voltage stability margin, steady-state frequency deviation, maximum transient frequency deviation and load shed amount. A modified system frequency response model is also proposed for frequency stability assessment. Multi-objective decision making (MODM) is performed using a combination of analytical hierarchy process, modified augmented e-constraint method and technique for order preference by similarity to ideal solution. The effectiveness of both the proposed model and MODM solution approach is extensively illustrated on a simulated model of Iran's power system in 2012.

Evolution Pathway Towards Wide Area Monitoring and Protection—A Real-World Implementation of Centralized RAS System

Remedial action scheme (RAS) is an automatic protection system designed to maintain system reliability. As result of green initiatives and mandates, there will be a proliferation of RAS in order to accommodate many new generation interconnections. With enabling technologies such as advanced intelligent electronic devices, fast computing technologies, utilities' extensive telecommunication network infrastructure, and the continued development of international standards, the opportunity allows a breakthrough in wide area monitoring and protection solutions. This paper describes how Southern California Edison systematically moved through stages from problem definition to ultimately deployment and system operation. Both the business and technical challenges during the project execution are discussed. Starting with the pressure on business practice, the evolutionary process of problem solving not only demonstrated how advanced information and telecommunication technologies can address the power utility business needs, but also paved a pathway for even more advanced wide area monitoring and protection applications.

Forewarned Is Forearmed: An Automated System for Remedial Action Schemes

The integrity of large-scale interconnected power grids may break down under system disturbances. The postdisturbance system may even turn out to cause a major blackout. To mitigate the undesired impacts of system disturbances, special protection systems (SPSs), also known as remedial action schemes (RASs), are widely used in modern power grids to safeguard their integrity.

A study of the application of fast valving and braking resistor for an intelligent SPS

There are some kinds of remedial action schemes that deal with sudden disturbance situations in a transmission network. Generator tripping with an SPS (Special Protection System) is one of the remedial action schemes, and it is a powerful and effective method of solving transient stability problems. When an extra-high-voltage transmission line that is transferring a large amount of power is tripped, generators designated by a SPS are tripped to prevent over-speeding of the generators. However, the tripping of generators can cause difficulties in the power system operation, and if large amounts of power are tripped, load shedding can occur. Therefore, it is desirable that a minimum number of generators is tripped in required stable conditions. For this purpose, an intelligent SPS is currently being developed to reduce the number of generator tripping events. In this paper, an application method involving fast valving and a braking resistor are analyzed as suitable action schemes for a SPS.

An Intelligent Wide Area Synchrophasor Based System for Predicting and Mitigating Transient Instabilities

Increasing expansion of power systems and grids are accompanied nowadays by innovation in smart grid solutions to maintain systems stability. This paper proposes an intelligent wide area synchrophasor based system (IWAS) for predicting and mitigating transient instabilities. The IWAS incorporates artificial neural networks (ANN) for transient stability prediction. The ANN makes use of the advent of phasor measurements units (PMU) for real-time prediction. Coherent groups of generators-which swing together-is identified through an algorithm based on PMU measurements. A remedial action scheme (RAS) is applied to counteract the system instability by splitting the system into islands and initiate under frequency load shedding actions. The potential of the proposed approach is tested using New England 39 bus system.

On the Accuracy Versus Transparency Trade-Off of Data-Mining Models for Fast-Response PMU-Based Catastrophe Predictors

In all areas of engineering, modelers are constantly pushing for more accurate models and their goal is generally achieved with increasingly complex, data-mining-based black-box models. On the other hand, model users which include policy makers and systems operators tend to favor transparent, interpretable models not only for predictive decision-making but also for after-the-fact auditing and forensic purposes. In this paper, we investigate this trade-off between the accuracy and the transparency of data-mining-based models in the context of catastrophe predictors for power grid response-based remedial action schemes, at both the protective and operator levels. Wide area severity indices (WASI) are derived from PMU measurements and fed to the corresponding predictors based on data-mining models such as decision trees (DT), random forests (RF), neural networks (NNET), support vector machines (SVM), and fuzzy rule based models (Fuzzy_DT and Fuzzy_ID3). It is observed that while switching from black-box solutions such as NNET, SVM, and RF to transparent fuzzy rule-based predictors, the accuracy deteriorates sharply while transparency and interpretability are improved. Although transparent automation schemes are historically preferred in power system control and operations, we show that, with existing modeling tools, this philosophy fails to achieve the “3-nines” accuracy figures expected from a modern power grid. The transparency and accuracy trade-offs between the developed catastrophe predictors is demonstrated thoroughly on a data base with more than 60 000 instances from a test (10%) and an actual (90%) system combined.

A Study of Optimal Nonfirm Wind Capacity Connection to Congested Transmission Systems

As wind is a low capacity factor source of power generation, a nonphysically firm connection strategy is key to its cost-effective and timely integration to presently constrained transmission networks. This paper, therefore, outlines the design and study of an optimal nonfirm wind capacity allocation model. While a precise statistical representation of wind power variations and geographical interdependency requires a significant number of data samples, the structured very-large-scale linear programming problem that results is shown to be exploitable by the Benders' decomposition scheme. Various wind capacity target levels are considered, and important sensitivity analyses are performed for multiple load profiles, wind profiles, and fuel price parameter values. Interestingly, the optimal wind capacity allocation is found to be reasonably robust to sizeable load and fuel price deviations, and while the effect of a limited historical wind data profile is more influential, the associated cost-function penalty is not significantly critical. The economic value of combining wind connection with advanced postcontingency network remedial action schemes is also highlighted.

Wide‐area monitoring and control using the real time digital simulator and a synchrophasor vector processor

AbstractSeveral major blackouts in the past have shown the need for advanced wide‐area monitoring and control (WAMC) techniques. Advanced synchrophasor visualization and monitoring can be realized with time‐referenced power system data that are collected by phasor measurement units (PMUs) using synchronized clocks. Presently, PMUs are being deployed around the world at a rapid rate for various power system applications. When a necessary number of PMUs are installed at optimal locations throughout the network, the complete state of the system can be observed. PMUs take real‐time measurements to determine the state of the power system and can be used to enhance state estimation efficiency. With PMUs in place, there are many control and protection schemes that can be implemented successfully to take preventive and corrective actions. These remedial action schemes (RASs) are classified by the IEEE Power System Relaying Committee (PSRC) as system integrity protection schemes (SIPSs). This work involved the development of a real‐time hardware test bed in order to analyze the transient stability of a simulated power system by using synchrophasors to visualize system stress across a transmission line with and without load‐shedding schemes. The real time digital simulator (RTDS®) was used to model the power system in real time. PMUs, a satellite‐synchronized clock, and a synchrophasor vector processor (SVP) were used to test the synchrophasor application. Copyright © 2010 John Wiley & Sons, Ltd.

Catastrophe Predictors From Ensemble Decision-Tree Learning of Wide-Area Severity Indices

Catastrophe precursors are essential prerequisites for response-based remedial action schemes, at both the protective and the operator levels. In this paper, wide-area-severity indices (WASI) derived from PMU measurements serve as the basis for building fast catastrophe predictors using random-forest (RF) learning. Given the randomness in the ensemble of decision trees (DTs) stacked in the RF model, it can provide at the recall stage not only an early assessment of the stable/unstable status of an ongoing contingency but also a probability outcome which quantifies the confidence level of the decision. This methodology, which to the best of our knowledge is new to the dynamic security assessment (DSA) of power systems, is also very effective in evaluating the importance of and interaction among the various WASI input features. Our research unexpectedly showed that the ensemble of trees in the RF is very robust in the presence of small changes in the training data and generalize across widely different network dynamics. Thus, the same RF performed very well on a large database with more than 60 000 instances from a test system (10%) and an actual (90%) system combined. One such a general RF (with 210 trees) boosted the reliability of a 9-cycle catastrophe predictor to 99.9%, compared to only 70% when a single conventionally trained DT is used.

Wide Area Protection—Technology and Infrastructures

Wide area measurements have been widely used in the energy management systems (EMS) of power systems for monitoring, operation, and control. In recent years, the advent of synchronized phasor measurements has added another dimension to the field of wide-area measurements. At the same time, the field of protection systems has been dominated by computer based relays, which make it relatively easy to communicate with relays and thus include them in many innovative protection systems. Special Protection Systems (SPS) or Remedial Action Schemes (RAS) are one example of integration of communication and protection systems. In recent years—due to operational demands imposed on transmission networks by deregulation it has become clearer that wide-area measurements and their integration in protection and control systems is a necessity. This paper documents the state-of-the-art in modern sensor, communication, and protection technologies which show great potential for innovations in protection and control systems for the future.

Wide-Area Protection and Power System Utilization

This paper describes basic principles and philosophy for wide-area protection schemes, also known as remedial action schemes (RAS) or system protection schemes (SPS). In the areas of power system automation and substation automation, there are two parallel trends in different directions: centralization and decentralization. More and more functions are moved from local and regional control centers toward the central or national control center. At the same time we also observe more and more "intelligence" and "decision-power" moving closer toward the actual power system process. We also see a great deal of functional integration, i.e., more and more functionality enclosed in the same hardware. This raises discussions concerning reliability (security and dependability). The main targets for this paper is therefore to: 1) sort out the terminology used in this area; 2) describe different application areas and related requirements; 3) illustrate different design principles-"top-down", "bottom-up", hierarchy, flat, etc., for different applications; and 4) identify similarities and differences between classic equipment protection and system protection-concerning philosophy as well as concerning product and system design. The theme of the paper is on the use of information technology to obtain more flexibility and smartness in power-system controls.

Potential DC system support to enhance AC system performance in the Western United States

The potentials of utilizing the controllability of DC lines to reduce the complexity of remedial schemes or to increase the stability performance of a system so that the impact of existing and future projects on nonproject systems can be minimized are explored. Less costly and perhaps more environmentally acceptable alternatives of utilizing power transfer overloads of the two existing DC lines of the Western Systems Coordinating Council (WSSC) in the Western US are presented. In addition, a concept to overload one DC line for the outage of the other DC line is investigated. Reducing the complexity of the remedial action scheme would be definite benefit to the WSCC network operating reliability objective.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power modulation of Sidney HVDC scheme. I. RAS control concept, realization and field tests

The 200 MW back-to-back Sidney (Nebraska) Converter Station (SCS) provides an asynchronous tie between the east and west AC power networks. In order to maintain electromechanical stability of the east network under worst-case line outage conditions, a remedial action scheme (RAS) was integrated in the HVDC (high-voltage direct-current) control. Basic components of the SCS RAS are frequency-dependent power modulation combined with an effective voltage control in the western network. The authors present the conceptual development of the RAS, as well as details on the RAS control hardware and software. Studies and live system tests have demonstrated the ability of the relatively fast HVDC controls to change the power infeed from the DC station quickly. These rapid changes in power transfer properly coordinated with speed deviation of a nearby generation unit, help maintain, and in some cases improve, the electromechanical stability of the AC system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power modulation of Sidney HVDC scheme. II. Computer simulation

For pt.I see ibid., vol.7, no.4, p.2145 (1989). The back-to-back Sidney (Nebraska) Converter Station (SCS) provides an asynchronous 200 MW tie between the east and west AC power systems of the United States. The addition of the SCS to the network required a remedial action scheme (RAS) integrated in the HVDC (high-voltage direct-current) control in order to meet AC systems reliability criteria. One of the basic components of the RAS is the frequency-dependent power modulation combined with an effective voltage control in the western network. Computer simulations were performed to check design and to provide initial settings for the RAS. As one part of the commissioning of the SCS, field tests of the RAS were conducted. The digital calculations were found to agree very well with the field test results. The simulation study covered two extensive AC networks with generators, their excitation control and speed-governing system representation, an HVDC with its standard controls, and the additional RAS for modulation and ramping of the power transferred.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application and implementation of fast valving and generator tripping schemes at Gerald Gentlemen Station

Remedial action schemes which respond to disturbance situations on the transmission network provide the transmission planner with an alternative means of improving system reliability and satisfying system design standards. A remedial action scheme based on a combination of momentary fast valving and generator tripping has been evaluated, implemented and tested by the Nebraska Public Power District in conjunction with its Gerald Gentleman Station. This scheme has enhanced system operating flexibility, provided the necessary reliability margins to comply with system design standards, and eliminated the need for costly generation reductions during prior transmission outage situations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>