Sreten Skuletic

Implementation of different methods for PTDF matrix calculation in flow-based coordinated auction

Flow-based coordinated auctioning (CA) is cross-border transmission capacity allocation mechanism. The South-East European (SEE) Transmission system operators (TSOs) launched the investigation of this method, based on better representation of physical behavior of interconnected electric systems than those widely used on most of the European borders. CA uses flow-factors (PTDF - Power Transfer Distribution Factors) to convert the commercial exchanges into their physical influence on the cross-border flows, and Border Capacities (BC) as physical limitations for those flows. The goal of this paper is to conduct a numerical comparison between different methods used for PTDFs calculation.

Influence of Combination Wave Generator's Current Undershoot on Overvoltage Protective Characteristics

Evaluation of the ability of equipment to withstand a wide variety of surges that can be expected to occur in low-voltage ac power systems, or of the performance of surge protective devices (SPDs) in dealing with this variety of surges, can be facilitated by a reduction of the database to a few representative stresses. IEEE Std. C62.41.2 and IEC Std. 61000-4-5 define the combination wave surge as a standard surge-testing waveform. However, these standards define different tolerances regarding the waveform undershoot of a short-circuit current surge delivered by the combination wave generator (CWG). In this paper, the influence of CWG short-circuit current undershoot has been analyzed for the case of one-stage protection with SPD located at the service entrance of the building. Simulation results for the model of the observed system in the Alternate Transients Program/Electromagnetic Transients Program and MATLAB, with experimental verification show that the short-circuit current undershoot of CWG has an influence on maximal values of voltages across load and energy deposited in SPDs.

Effective protection distance from cascade coordinated Surge Protective Devices to equipment in low-voltage AC power circuits

Protection of the equipment in low voltage AC power circuits against surges is based on wide application of surge protective devices (SPDs). Cascade application of SPDs located at the service entrance of a building and near sensitive equipment is intended to ensure optimal energy distribution among installed SPDs, as well as proper equipment protection against surges. In the paper, scenarios of surges that are impinging at the service entrance of the building of interest and application of two-stage cascade protection have been analyzed. The influence of different cables lengths: arrester - suppressor (A-S) and suppressor - load (S-L), as well as influence of type and parameters of load on SPDs protection characteristics have been analyzed and discussed. Simulation programs ATP/EMTP and MATLAB are being used for analysis of several load types, namely resistive, inductive, capacitive, resistive - inductive and resistive -capacitive load, with the parameters of real devices which can be found in low-voltage AC power circuits. Performed analysis should to point on characteristics of loads and connecting cables which provide regular protection.

Contribution to Calculation of Switching Overvoltages Originated by Line Energizing in the Networks with Lumped Parameters

The possibility, which can make the calculations and analysis of switching overvoltages originated by line energizing faster and easier by using relatively simple, but exact enough, derived mathematical method and computer application, has been presented and discussed in this paper. The calculations and analysis are performed by using Laplasian transformations in the networks with lumped parameters. Line is represented with cascade array of segments that are modeled with T or Pi equivalent schemes. By using derived mathematical model of the observed system and applied method, the computer program written in MATLAB, which enables very quick and quite easy calculations of overvoltages, as well as their graphical presentation, has been made. Derived program has been used for the analysis of a number of switching overvoltages originated by line energizing for the different real cases, which are the most frequent ones used in the practice. Obtained results have been compared with the results of switching overvoltages simulation with traveling wave methods

Possibility of computer application for calculations of switching overvoltages originated by capacitive current’s tripping

The possibility, which can make the calculations and analysis of switching overvoltages originated by capacitive currents tripping faster and easier by using relatively simple, but exact enough, derived mathematical method and computer application, has been presented and discussed in the paper. By using derived mathematical model of the observed system and applied method, the computer program written in MATLAB, which enables very quick and quite easy calculations of overvoltages, as well as their graphical presentation, has been made. A number of switching overvoltages originated by opening of an unloaded overhead line for the different real cases of the elements data and different time functions of dielectric withstand restoration in breakers inter-contacts area have been analyzed. Calculated results have been compared with the results obtained by using well known ATP/EMTP program, and used for the analysis of the advantages and disadvantages of the proposed simple procedure and for validation of the introduced improvements.

Experimental investigations of switching overvoltages in 110 kV network of power system of Montenegro

A part of comprehensive experimental investigations of switching overvoltages in the segment of 110 kV transmission network of the electric power system (PS) of Montenegro is given, analyzed and discussed. The performed experimental investigations are the first investigations of such kind of problems ever performed in the transmission network of PS of Montenegro. A number of obtained very valuable data allows complex and sensitive analysis not only about the characteristics of the possible switching overvoltages which can appear during the period of exploitation, but also about their influences on the observed lines and their elements, as well as on the segment of the observed transmission network. The measured data could be also used for the risk assessment and analysis of the electric breakdown of the insulation of lines, as well as for the drawing the recommendations and conclusions about future exploitation and possible improvements of the particular components and the entire observed system.