Large Disturbances In Power System Research Articles

A New Adaptive Underfrequency Load Shedding Scheme to Improve Frequency Stability in Electric Power System

This paper proposes a new adaptive underfrequency load shedding scheme (UFLS) to avoid frequency instability in electrical power system during abnormal wide area disturbances. The developed scheme is based on online monitoring of the distance relay zone 3 decisions of some tie lines using (WAMS) and SCADA/EMS systems, to check rapidly and reliably the uncontrolled islanding conditions and, permit an automatic load shedding action to maintain frequency stability of power system. Simulation results on 400 kV Turkish transmission systems demonstrated the effectiveness of the proposed scheme compared to current frequency load shedding schemes which they cannot consider all possible circumstances because of their limited access to the power network data. Simulation results clearly indicate that large disturbances in power systems can be avoided and their propagation can also be stopped using the proposed scheme.

Speedy Detection of Symmetrical Faults During Power Swing

Small and large disturbances in power system may sometimes lead to sustained oscillation in three-phase power, often termed as ‘power swing’ in the literature. Power swing is a balanced phenomenon and may be indistinguishable from a three-phase fault. Transmission lines being protected by distance relays may be incorrectly de-energized because of a power swing. So, three-phase faults should be discriminated from power swing with high reliability and dependability. In this study, a novel symmetrical fault detection technique has been proposed with dual use line relays for the first time. The proposed algorithm has been verified for a large number of fault scenarios including series compensated lines with single machine infinite bus and western system coordinating council-9 bus system. It has been seen that the proposed algorithm is giving fast detection of three-phase faults during power swing with high accuracy.

Fast and Accurate Frequency Response Estimation for Large Power System Disturbances Using Second Derivative of Frequency Data

Accurate Frequency Response Estimation (FRE) is critical to reliability risk management of large power system disturbances. This letter proposes a measurement-driven approach for FRE by calculating the second derivative of frequency from synchrophasor data. Compared with conventional methods, the proposed method has major advantages of low computational burden and high accuracy, which makes it appropriate for real-time FRE in bulk power systems. The effectiveness of this method is validated with actual synchrophasor data on 96 confirmed historical power system disturbances in the U.S. eastern interconnection.

Impact of Low Data Quality on Disturbance Triangulation Application Using High-Density PMU Measurements

High-density PMUs can be implemented to estimate the location of a large power system disturbances based on the theory of Time Difference of Arrival (TDOA). Unfortunately, real-world measurements suffer from low data quality issues frequently caused by various uncontrollable and unpredictable factors. In this paper, four types of practical low data quality issues from onsite PMUs are first identified from the industry perspective. Then, the impacts of each low-quality data issue on disturbance triangulation are explored using real-time measurement cases from Jiangsu power grid with a high-density PMU network. This paper provides valuable guidance for utility operators and academic researchers to use actual PMU data for power grid applications.

Modeling Protection Systems in Time-Domain Simulations: A New Method to Detect Mis-Operating Relays for Unstable Power Swings

Large power system disturbances can cause stable or unstable power swings. Unstable power swings result in generator pole slipping. A generator or group of generators may accelerate or decelerate, leading to voltage depression at the electrical center along with generator tripping. This voltage depression may cause protective relay mis-operation and unintentional separation of the system. In order to avoid unintentional islanding, the potentially mis-operating relays should be blocked from tripping. This paper proposes a novel method to determine the location of the mis-operating relays at the planning phase. Blocking these mis-operating relays, combined with an appropriate islanding scheme, help avoid a system-wide collapse. The proposed method is tested on data from the Western Electricity Coordinating Council. A triple line outage of the California-Oregon Intertie is studied. The electrical center is determined and appropriate out-of-step blocking schemes are identified. The results show that the correct design of out-of-step protective relays improves the dynamic performance of the power system and causes less fluctuations in voltage and frequency throughout the system.

English

Now a days electrical system becomes very much large and Power demand will be increasing more and more. To satisfy the power demand nonconventional sources are incorporated in the field of electrical power generation and the system becomes Inter connected. Large power system disturbances sometimes causes interconnected system to become separated into some islands and it has either surplus of generation or load. If generation is more than it can be controlled by controlling the speed of speed governors connected with the generating station will result into change in frequency. This paper includes the derivation of simple low order system frequency response (SFR) model that can be used for estimating the frequency behaviour of the interconnected power system to sudden load disturbances. The SFR model is the simplify model to analyse system dynamics.

Secured Zone 3 Protection During Stressed Condition

Maloperation of the zone 3 element of distance relays during stressed system conditions, such as power swing, load encroachment, or voltage stressed condition is one of the main reasons for large disturbances in power systems. The improved protection technique for zone 3 can help to prevent such maloperation and, thus, more reliable power systems can be envisaged. This paper proposes an algorithm that utilizes two new criteria: 1) the maximum value of the transient monitoring function obtained from three-phase currents and 2) the phase angle of the positive-sequence impedance to support zone 3 of the distance relay. The technique is tested for various power system events, such as the three-phase fault during the power swing, load encroachment, voltage stressed conditions, and current-transformer saturation during the three-phase fault using data simulated through EMTDC/PSCAD in the IEEE 39-bus New England system. The simulation results show that the zone 3 protection scheme using the proposed technique can correctly discriminate the three-phase fault from stressed system conditions.

Risk evaluation of online special protection systems

Special Protection Systems (SPSs) are one of efficient tools to limit the consequences of instability in case of happening large disturbances in power systems. Generator Rejection Systems (GRSs) are the mostly used forms of SPS. Offline GRS suffers from drawback of inaccuracy and increased risk when power system operating point differs from the nominal value. By predicting the future trend of bus phase angles, online GRS offers a lower risk than the offline scheme, especially when its parameters are appropriately tuned. In this paper, the effect of online GRS parameters including the starting time and width of the data window used for prediction on its performance is thoroughly investigated. The risk analysis of online GRS is evaluated under different conditions and compared with that of offline and no GRS schemes. To enhance the efficiency and accuracy of online GRS, an optimal data window is proposed. As an intriguing result, using a wider data window does not always result in a better accuracy of online GRS and the starting point of the data window has a vital effect on the performance of online GRS. The GRS schemes are tested on the WSCC test system and results are discussed in detail.

Power System Modeling for Inverse Problems

Large disturbances in power systems often initiate complex interactions between continuous dynamics and discrete events. The paper develops a hybrid automaton that describes such behavior. Hybrid systems can be modeled in a systematic way by a set of differential-algebraic equations, modified to incorporate impulse (state reset) action and constraint switching. This differential-algebraic impulsive-switched (DAIS) model is a realization of the hybrid automaton. The paper presents a practical object-oriented approach to implementing the DAIS model. Each component of a system is modeled autonomously. Connections between components are established by simple algebraic equations. The systematic nature of the DAIS model enables efficient computation of trajectory sensitivities, which in turn facilitate algorithms for solving inverse problems. The paper outlines a number of inverse problems, including parameter uncertainty, parameter estimation, grazing bifurcations, boundary value problems, and dynamic embedded optimization.

Switching control for power systems with line losses

The control of initial swinging due to large power system disturbances justifies the use of controllers in a full-on full-off mode. Current control designs are based on linear controllers with saturating elements using local feedback signals. The paper develops a switching control strategy for the damping of power system interarea modes using multiple FACTS devices and angle transducers. The design is based on maximising the convergence rate of a system kinetic energy function. The function provides correct analysis of lossy systems so that the the load modulation by static VAr compensators, as well as the damping from controlled series capacitors, can be incorporated. Fast suppression of oscillations using multiple FACTS devices is demonstrated.

Light water reactor plant modeling for power system dynamics simulation

Models have been developed for simulating the plant dynamics of light-water-reactor (PWR and BWR) plants under both small and large power system disturbances. The model permits precise and effective analysis of the dynamics of the nuclear plant response to power system faults by combining the plant model with the conventional power system dynamics simulation program. The modeling of the nuclear plant is described, and the application of the model to power system dynamics simulation is outlined. >