Search

Service interruptions have a significant impact on society and therefore the main objective of power system planning and operation is to ensure that they do not happen. Because voltage instability is one of the dynamic phenomena that may result in a system-wide blackout, this type of stability problem has been an important research topic for many years. Grid developments, like the increase of Renewable and Distributed Generation (RDG) and the impact of deregulation, in combination with the steadily increasing electricity demand, will have its impact on the vulnerability of the power system to voltage stability problems. On the other hand, developments in power system monitoring and control such as the use of accurate Phasor Measurement Units and the development of Smart Grid control concepts, introduce new possibilities for voltage instability prevention. In this work the impact of having a large share of RDG capacity on voltage stability is investigated and a new Hierarchical Agent-Based Voltage Instability Prevention (HABVIP) system for online voltage instability emergency control is proposed. The control philosophy uses the maximum loadability index to determine the amount of active and reactive power load relief necessary to restore stability. The intelligence for this control is provided by agents located in the substations: the substation agents. The load relief is obtained by: increase of local generation, virtual load shedding via adjusting the load tap changers set point, intelligent load control and increasing the reactive power output of Static Var Compensators. The control of the actuators is provided by agents located in the actuators: the actor agents. Verification of the system is done by off-line simulations and by building a real-time hardware in the loop demonstration model.

In this paper, we propose a black box model for low-voltage arcs. This model is based on the classical theory with the addition of a corrective term to better fit the small current phase, which is seen to be crucial in determining arc extinction. The model is physically consistent, accounting for nonequilibrium effects in a cold plasma. A mathematical algorithm is proposed for model parameter identification, solving a constrained optimization problem by suitably coupling gradient moves with heuristic search methods. Black box modeling is applied to industrial circuit breakers and very good agreement between model predictions and experiments is observed.

Distributed generation (DG) plays an increasing role in the power system. Due to their local character they could in principle be used in emergency situations to prevent a blackout. Classically, however, DGs are uncontrollable. In this paper methods are proposed to use DG as actuator in the Hierarchical Agent-Based Voltage Instability Prevention (HABVIP) system. The control strategy in this system is to obtain a certain amount of load relief in the problem area. Three types of DG are considered: micro-CHPs, greenhouse CHPs and Wind Turbines (WT). For the micro-CHP and greenhouse CHP the output power can be controlled within limits. These limits are determined by the maximum temperature settings. For the micro-CHP a Virtual Power Plant (VPP) scheme is proposed to obtain continuous power output of a group of micro-CHPs that work under thermostatic control. For the WT the output power cannot be controlled. For that reason a method is proposed to use the predicted power generation of this turbine to anticipate for an increase or decrease. The proposed methods are verified by simulations which show that the methods work properly.

In this paper a strategy is introduced for emergency control of Load Tap Changers (LTCs) to prevent the system from voltage collapse. The method is based on the fact that the power consumed by constant current and constant impedance loads can be lowered by decreasing the secondary voltage of the LTC. This idea is used to develop a method of indirect load shedding. This method calculates, based on a model of the connected load, the voltage set-point of the secondary side of the LTC for a given amount of load that needs to be shed. With simulations it is demonstrated that a LTC can be applied for load relief using the proposed method. A sensitivity analysis is done to study the effect of an error in the load model parameters. Furthermore it is proven that the method can be used to prevent the power system from a typical voltage instability. Finally a proposal for the implementation in a smart grid multi-agent system is presented.

This paper presents the advantages of using wind speed time series models from ARMA-GARCH class. The models are found using good statistical practice and are able to capture the most important characteristics of the data like distribution, time dependence structure and periodicity in a satisfying manner. It is shown that the models offer several crucial advantages. The artificial wind speeds simulated from the obtained models are statistically indistinguishable from the wind speed time series measurements recorded in other years than the original data. Moreover, models can contribute to the considerations of extreme scenarios of wind power generation by simulating wind speeds characterized by a very high energy content. Thanks to the use of continuous cdf transformations, the synthetic time series do not possess the measurement error.

In the Dutch power system the power consumption is increasing while the transmission and distribution system capacity is not increasing at the same rate. Furthermore due to the increasing amount of decentralized generation, by for example micro-CHP units and wind turbines, the power flows in the power system are changing. In weak sub-transmission and distribution grids an increase in the number of voltage stability problems is expected. However: with the large share of decentralized generation we have the solution for voltage problems already there. In this paper we propose a new Hierarchical Agent Based Instability Protection System. In this paper the idea is described and a theoretical justification is given, in a later stage of the project we will verify the system with the Real-time Digital Simulator and external controls.

The fast growing application of sustainable energy sources imposes major structural changes on the current electric power systems. One of these structural changes is to make use of large variable speed wind turbines within the conventional electrical power networks. The installation of these wind turbines has, indeed, indispensable impacts on the dynamic behavior of the existing electric power systems. Thus, it is important to gain a rather generalized overview on how these wind turbines, which mostly use Doubly Fed Induction Generators (DFIGs), affect the system stability. This paper performs an analytical analysis for the indication of small disturbance rotor angle stability in the power systems equipped with variable speed wind turbines using DFIGs. Also, in order to consider the stochastic characteristic of the sustainable energy sources, the paper applies an iterative-stochastic method to analyze the small disturbance angle stability. The suggested iterative-stochastic methodology is numerically verified, within this paper, by getting applied to an electric power test system.

State estimation is an important tool for system operators. The state of the power system is defined by the voltage magnitudes and phase angles at all buses. The state estimator (SE) determines this state based on a set of redundant measurements.