Ivica Pavić

Selection of Surge Protective Devices for Low-Voltage Systems Connected to Overhead Line

This paper presents a procedure of choosing an appropriate surge protective device for low-voltage systems connected to an overhead line. For a typical surge protection application, an appropriate Electromagnetic Transients Program model is devised. The energy overload is calculated for a surge protective device following a simulation of the lightning effect. This way, it is possible to determine the required class for the surge protective device in question. The procedure has been tested on some typical overhead low-voltage networks. The results of these calculations, as well as very good service experiences, demonstrate that the use of Class II surge protective devices seems to be appropriate for service entrances in buildings that have no lightning protection systems.

Artificial neural networks in power system topology recognition

This paper presents an artificial neural network based model for identifying anomalies in the reported power system topology. The results obtained using a multilayer perceptron with backpropagation learning algorithm are presented and discussed.

Power system equivalent based on an artificial neural network

Very often, insufficient data is exchanged between neighboring power systems for quality load flow and contingency analysis. The external systems, therefore, have to be substituted with the power system equivalents. In this paper the possibilities of using an artificial neural network as the external power system equivalent is explored, to be used for load flow and contingency analysis within the internal power system. The experiment is performed on a standard IEEE 24-node network which is, for the purposes of testing, divided into two systems (the internal and the external) and the external system is modeled by a neural network. The results are presented and discussed.

Area voltage and reactive power optimization based on interconnection reactive power flow control

A method for optimal power system voltage and reactive power management which takes into account control of the interconnection reactive power flows is presented in this paper. The need for such control is evident as the voltage and reactive power scheduling in one power system can have serious impacts, including very negative, on the neighboring power systems. Moreover, according to the ENTSO-E network code, the neighboring transmission system operators (TSOs) should commonly define the reactive power flow limits on the interconnectors. The proposed solution is based on a modified single-area reactive power optimization (RPO) method. Reactive power flow constraints on the interconnectors were implemented in the reactive power control model. The presented approach does not require complex coordination or exchange of information between the neighboring TSOs, and is easy to implement. The efficiency of the presented method is evaluated using the New England 39-bus system.

Control variable selection for the corrective control of voltages and reactive power flows

A sequential search strategy for the control variable subset selection, used for optimal power system voltage control and reactive power management, is presented in this paper. The objective of the presented selection method is to eliminate the redundant control variables which have small impact on the reactive power optimization (RPO) objective function and/or constraints. Selected control variable set is used for correcting the power system state in which the operational limits are violated. The candidate control variables are evaluated based not just on their impact on the out-of-bound variables, but also on the overall power system state. Sensitivity analysis, based on power flow calculation, was conducted for each candidate control variable and the results were used as an input data for the sequential search method. Considering the RPO is inherently a mixed integer nonlinear programming (MINLP) problem, the genetic algorithm (GA) was used for solving the optimization problem. The efficiency of the presented method was tested on IEEE test systems. Simulation results are presented for IEEE 118-bus test system.

Power Flows and Transmission Losses in the Croatian Network after the UCTE Reconnection

Consideration of losses of electric energy in the transmission network is important for power system operation and control. Development of the remote control system in the Croatian National Control Centre enabled an accurate calculation of losses and their comparison with the results measured in the terminal nodes. Additional value in proposed way of determination of losses lies in the fact that losses can be allocated by voltage level, lines and transformers. A new way of calculating the percentage of losses is proposed by the authors

Modern technology in control center operation

The development of computer technology enabled significant improvements in dispatching centers. That was especially important for Croatian Electricity that was faced with a prospect of a new way of operation with new functions and responsibilities. The financial situation did not allow complete replacement of the computer system and its software support. This paper describes the interconnection of the new hardware with the existing hardware, improvements and new technologies introduced to control center operation and the development of a new control system.