Vladan Radulović

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.

The Impact of the Load Side Parameters on PC Cluster's Harmonics Emission

Harmonics current emission from personal computers (PCs) is of special interest to power quality researchers, due to their wide spread application and the fact that they are usually co ...

Multi-parameter mathematical model for determination of PC cluster total harmonic distortion of input current

Purpose – Low power devices with switched-mode power supply represent harmonic generating apparatus in widespread use nowadays. The influence of personal computers (PCs), which affect the supply voltage, is considered. Harmonic level due to simultaneous PC operation is quantified by the total harmonic distortion of input current (THD I ). The purpose of this paper is to propose a multi-parameter mathematical model for the THD I calculation. The model is convenient for practical engineering application. Design/methodology/approach – The model is derived using the measured and simulated data. The model coefficients are obtained in the least squares sense. Findings – Mathematical modeling of THD I is the least expensive and the most convenient solution for engineering application. The models proposed in the literature have many drawbacks, which motivated the authors to develop a more comprehensive solution. Grid stiffness, capacitance of PC power supply unit and PC cluster size represent the major parameters...

Characteristics of Overvoltage Protection with Cascade Application of Surge Protective Devices in Low-Voltage AC Power Circuits

Surge Protective Devices (SPDs) are widely used for protection of the equipment in low-voltage AC power circuits against wide variety of surges. Cascade application of SPDs starting at ...

Least Squares Modeling of Voltage Harmonic Distortion Due to PC Cluster Operation

Regarding the possibility of harmonic generation, personal computers (PCs) are very significant within the category of non-linear low power loads. In modern distribution systems, the number of PCs simultaneously connected to distribution grid constantly increases. This PC clustering can negatively affect the quality of supply. The paper deals with mathematical modeling of the voltage total harmonic distortion (THDU) caused by operation of PC cluster. The proposed model is based on the power quality measurements carried out in a computer centre and computer simulations. It takes into account the THDU dependence on the PC cluster size and grid stiffness. Model parameters are derived in the least squares sense. The influences of cable cross-section and pre-existing THDU of the phase voltage are also discussed. The accuracy of the proposed model is confirmed by additional measurements performed in a commercial building.

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

The requirements for efficient overvoltage protection of electronic devices in low-voltage power systems

Original scientific paper The increasing sensitivity of electronic devices widely used in low-voltage AC systems requires an appropriate protection against voltage and current surges. Protection of the equipment against the prospective surges is based on application of surge protection devices (SPDs). Most common situation, especially in residential buildings, is application of only one SPD at distribution board. In the paper, comprehensive analysis of this type of overvoltage protection system with wide ranges of influencing parameters is performed through experimental measurements and number of simulations. Obtained results show that existence of built-in varistors within electronic devices, with low protection voltages causes their thermal destruction due to inadequate distribution of surge energy between SPD and varistors. The requirements for efficient protection system which will provide survival of built-in varistors, as well as proper overvoltage protection characteristics are described and discussed in the paper.

Effects of Different Combination Wave Generator Design on Surge Protective Devices Characteristics in Cascade Protection Systems

Cascade application of surge protective devices (SPDs) in low-voltage ac power circuits is intended to ensure proper equipment protection against surges as well as to provide surge energy distribution between SPDs. In order to evaluate equipment response and SPDs performance, concept of representative surges, which can be used for surge testing purposes, is introduced by international standards. Combination wave surge is defined both by IEEE C62.41.2 standard and IEC 61000-4-5 standard as one of the representative surges. However, these standards specify different tolerances regarding short-circuit current waveforms undershoot delivered by combination wave generator (CWG). The aim of this paper is to investigate the influences of different CWGs regarding short-circuit current undershoot in cascade two-stage protection system. It will be shown that differences that appear during surge testing with application of different CWGs can lead to inappropriate selection of SPDs regarding energy absorption capability and/or protection level.

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.