Papers by Zijad Bajramovic
The problem of pulse voltage measurements in the nanoseconds range has become of great importance... more The problem of pulse voltage measurements in the nanoseconds range has become of great importance with ongoing problems related to the construction of pulse fusion generators as well as with simulations of electromagnetic pulses related to the atmospheric nuclear explosion. Ultrafast pulses in the nanoseconds range can be measured by the capacitive voltage divider. The problem that arises with ultrafast voltage occurrence is inductivity. Under conditions of the nanoseconds pulse increase rate, conductors of about few centimeters should be regarded as inductivity. Therefore, capacitive divider can be treated as an equivalent RLC circuit. The ohmic resistance R in that equivalent circuit originates from the characteristic impedance (either 50 Omega or 75 Omega) and, depending on its design, it can introduce an additional parasite inductivity. The aim of this paper is to consider and analyze the constructive solutions of capacitive voltage divider for measuring ultrafast voltage occurr...
2017 2nd International Multidisciplinary Conference on Computer and Energy Science (SpliTech), 2017
This paper deals with investigation of the impulse characteristics of transmission line tower gro... more This paper deals with investigation of the impulse characteristics of transmission line tower grounding. Investigations of the impulse characteristics of transmission lines tower grounding in this paper are based on experimental analysis conducted on type “A” grounding of transmission line tower. Firstly, paper describes the problem of back-flashover and impact of transmission lines tower grounding impedance on it. Also, experimental investigation of impulse characteristics with different rise time of current wave front on real type “A” grounding are given. Finally, detail analysis of experimental data is given.
Tokom 2009. godine je na podrucju Hrvatske uspostavljen sustav za lociranje munja (SLM, eng. Ligh... more Tokom 2009. godine je na podrucju Hrvatske uspostavljen sustav za lociranje munja (SLM, eng. Lightning Location System - LLS) kao dio Europskog sustava LINET. Sustav je razvijen na Sveucilistu u Munchenu u Njemackoj i danas broji preko 125 senzora diljem Europe. Sest senzora je instalirano na podrucju Hrvatske te dva na podrucju Bosne i Hercegovine. Prve analize podataka ukazuju na zadovoljavajucu ucinkovitost detekcije (eng. Detection Efficiency - DE) koja prelazi 90% za atmosferska pražnjenja oblak-zemlja i zadovoljavajucu tocnost lociranja (eng. Location Accuracy - LA) sa statistickom pogreskom ispod 300 m za podrucje Hrvatske. U razvoju je programska podrska za pracenje grmljavinske aktivnosti u realnom vremenu, analizu povijesnih grmljavinskih aktivnosti, statisticku obradu podataka, korelaciju podataka o grmljavinskim aktivnostima s položajem dalekovoda i izradu karata gustoce grmljavinske aktivnosti. U clanku je prikazana razvijena programska podrska za primjenu podataka o ud...
IEEE Transactions on Plasma Science, 2008
In this paper, switching overvoltages due to disconnector switching in air-insulated substations ... more In this paper, switching overvoltages due to disconnector switching in air-insulated substations (AISs) are presented. Measurements of these switching overvoltages were performed in the AIS Grabovica (Hydro Power Plant-HPP Grabovica) on River Neretva and the AIS Kakanj (Thermo Power Plant-TPP Kakanj). These power plants are important objects for operation of Bosnia and Herzegovina's electric power system. Investigations of operating of air-disconnector-type centre break was performed in order to determine switching-overvoltage levels on primary and secondary circuits that can lead to relay tripping in AIS Grabovica and AIS Kakanj. During operations of disconnector (synchronization or disconnecting of generator from network), malfunctions of signaling devices and burning of supply units of protection relays appeared. At the same time, sparking between primary terminals of the instrument current transformer occurred. The influence of resistance of electric arc between the contacts of the disconnector is analyzed. Computer simulations by means of alternative transients program-electromagnetic transients program are performed. Differences between the measured and the calculated values were under 4.52% for overvoltage factor and under 2.56% for overvoltage wave frequency. Comparison of the transient computer simulations with the field measurements showed that calculations could be used for the assessment of the transient overvoltages caused by disconnector switching.
This paper presents measuring results of transferred overvoltages in the secondary circuits of in... more This paper presents measuring results of transferred overvoltages in the secondary circuits of instrument transformers caused by switching operations of disconnector in air insulated substations 220 kV, in Bosnia and Herzegovina. Obtained results show that the maximum amplitude of these overvoltages can be up to 940 Vpeak (220 kV hydroelectric power plant Grabovica). In order to ensure electromagnetic compatibility it is necessary to adequately damp high overvoltages by instrument transformer, or to use some of the measures for reducing transferred overvoltages in secondary circuits. The conducted measurements show that in case of using unshielded secondary cables on current transformer terminals, overvoltages are much higher than in case of using shielded cables (3.7 times higher in measuring core and 6.1 times higher in protective core). Paper gives suggestions for eliminating the causes of interference, reducing coupling on the path of signal transmission and increasing protectio...
Abstract. In the paper are presented results of switching overvoltages investigations, produced b... more Abstract. In the paper are presented results of switching overvoltages investigations, produced by operations of air disconnector rated voltage 220 kV. Measurements of these switching overvoltages are performed in the air-insulated substation HPP Grabovica on River Neretva, which is an important object for operation of electric power system of Bosnia and Herzegovina. Investigations of operating of air disconnector type Centre-Break were performed in order to determine switching overvoltage levels that can lead to relay tripping in HPP Grabovica. During operations of disconnector (synchronization or disconnecting of generator from network) malfunctions of signalling devices and burning of supply units of protection relays were appeared. Also, results of computer simulations using EMTP-ATP [1] are presented. Key words: Switching overvoltages, air disconnector, air insulated substations, secondary circuits.
Lecture Notes in Networks and Systems
In practice are used several neutral point grounding modes for medium voltage grids. Each mode ha... more In practice are used several neutral point grounding modes for medium voltage grids. Each mode has certain advantages, but also disadvantages. Therefore, for the final decision on the grounding method a special analysis is performed for each transformer substation, given the specificity of the distribution grid connected to it. Neutral point treatment also affects the reliability of electricity supply to consumers, which in conditions of an open electricity market is gaining more and more importance. Along to the technical of great importance is the economic aspect as some solutions differ significantly. This paper gives a specific review of basic technical characteristics for solutions with compensated (resonant) grounding of the neutral point, i.e. application of Arc Suppression Coil (ASC)-Peterson coil technology in distribution grids, which implies neutral point grounding of the power transformer through an inductive reactance. Also in the paper are given basic principles of applied protections as well as modern approaches for failure detection in distribution grids with compensated neutral points.
This paper provides an analysis of the impact of mini hydropower plant “Kordici” on the 20 kV dis... more This paper provides an analysis of the impact of mini hydropower plant “Kordici” on the 20 kV distribution network of Bugojno area in terms of power quality. Therefore, measurement and evaluation of the quality of the supplied power was carried out at the point of common coupling between the mini hydropower plant and the distribution network. Measurement was carried out for the period from March 7 to March 18, 2016 and the data were evaluated in accordance with EN 50160 standard.
Ferroresonance is a nonlinear dynamic phenomenon that appears in the electric power system betwee... more Ferroresonance is a nonlinear dynamic phenomenon that appears in the electric power system between a non-linear inductances and system capacities excited by a sinusoidal voltage source. The most common non-linear elements of the electric power system are the iron core inductances of power and measuring transformers, reactors, etc. in which saturation of non-linear elements can occur. As a consequence of ferroresonance there may be a significant increase in the voltage value and under the certain conditions an excessive increase of the current value across the transformer terminals. This phenomenon can lead to damage of the measuring transformers and other equipment used in the network. Ferroresonance is one of the most common low-frequency electromagnetic transient phenomena that appear in the isolated power networks. Therefore, special attention must be on analyzing the probability of ferroresonance occurrence in electric power systems. In this paper, ferroresonance measurement results will be given. The waveform of the phase to ground voltage and wave form of the open delta voltage is obtained. Also, the Fourier transformation is performed on these signals. Proposed measurements are conducted in the real 35 kV distribution network with isolated neutral point. Also, efficiency of some experimentally tested mitigation measure will be presented within this paper.
Advanced Technologies, Systems, and Applications III, 2018
A power system state estimation is one of the most important applications in the power system con... more A power system state estimation is one of the most important applications in the power system control center. Power systems are continuously monitored in order to determine a reliable data of the state variables. Conventional power system state estimators, which are iterative and less accurate, are subject to important changes because of the extensive use of Phasor Measurement Units (PMUs). Although there are many advantages related to their use, PMUs are highly expensive and cannot be implemented at all buses. Therefore, it is very important to find an optimal number of PMUs and their locations in power system to achieve full observability. This paper presents an overview of different techniques for power system state estimation. It also investigates the outcomes of including PMUs in conventional state estimation process. The effectiveness of the proposed state estimation techniques is validated using IEEE test system with 14 buses.
In the paper are presented results of switching overvoltages investigations, produced by operatio... more In the paper are presented results of switching overvoltages investigations, produced by operations of air disconnector rated voltage 220 kV. Measurements of these switching overvoltages are performed in the air-insulated substation HPP Grabovica on River Neretva, which is an important object for operation of electric power system of Bosnia and Herzegovina. Investigations of operating of air disconnector type Centre-Break were performed in order to determine switching overvoltage levels that can lead to relay tripping in HPP Grabovica. During operations of disconnector (synchronization or disconnecting of generator from network) malfunctions of signalling devices and burning of supply units of protection relays were appeared. Also, results of computer simulations using EMTP-ATP [1] are presented.
2019 International Symposium on Electromagnetic Compatibility - EMC EUROPE, 2019
In this paper impact of the tower arrangements on the mitigation of the increased values of the e... more In this paper impact of the tower arrangements on the mitigation of the increased values of the electric field intensity at high-voltage transmission line conductors was investigated. Several configurations of high-voltage towers (horizontal, delta, reverse delta, vertical and split-phase configurations) were analyzed. It assumed that the same height of the lowest phase conductors above the ground and the same value of the connected 400 kV voltage. The calculations were carried out for the values of the electric field intensity on the surface of the conductor and its immediate vicinity. A charge simulation method was used to calculate the electric field intensity on the surface of the stranded conductors and their immediate vicinity.
In practice are used several neutral point grounding modes for medium voltage grids. Each mode ha... more In practice are used several neutral point grounding modes for medium voltage grids. Each mode has certain advantages, but also disadvantages. Therefore, for the final decision on the grounding method a special analysis is performed for each transformer substation, given the specificity of the distribution grid connected to it. Neutral point treatment also affects the reliability of electricity supply to consumers, which in conditions of an open electricity market is gaining more and more importance. Along to the technical of great importance is the economic aspect as some solutions differ significantly. This paper gives a specific review of basic technical characteristics for solutions with compensated (resonant) grounding of the neutral point, i.e. application of Arc Suppression Coil (ASC)—Peterson coil technology in distribution grids, which implies neutral point grounding of the power transformer through an inductive reactance. Also in the paper are given basic principles of app...
Advanced Technologies, Systems, and Applications IV -Proceedings of the International Symposium on Innovative and Interdisciplinary Applications of Advanced Technologies (IAT 2019), 2019
In this paper, is describe coordinated auctions of cross-border transmission capacities between S... more In this paper, is describe coordinated auctions of cross-border transmission capacities between South East European Transmission system Operators through the operation of the regional company “Coordinated Auction Office in South East Europe” (SEE CAO). The main objective is to acquaint with the specific processes, functions, modules and contributions of the first regional company in the area of South-Eastern Europe. The importance of SEE CAO is reflected by upgrading previous unilateral auctions performed by each TSO on 50% of NTC (Net Transmission Capacity) following their national Auction Rules or bi-lateral auctions performed by two neighboring TSO (Transmission system operator) on 100% of NTC following bilateral Auction Rules to regionally coordinated auctions performed by SEE CAO, using one single set of the Auction Rules and the possibility for the traders to allocate cross-border capacity from Croatia to Turkey by using SEE CAO as one-stop-shop. At the end of the paper, the r...
Base stations for mobile telephony are often exposed to the direct lightning strikes, which can l... more Base stations for mobile telephony are often exposed to the direct lightning strikes, which can lead to the significant damage of telecommunication equipment, measuring equipment and other electronic equipment within the base station. This paper describes methods of assessing the stochastic efficiency of the lightning protection systems of the mobile cellular base stations. In this paper Monte Carlo method is applied and electrogeometric model, which were used for the simulation of random natural of the lightning strikes. The presented methodology was applied on the example of high tower base station.
Lecture Notes in Networks and Systems
This paper presents a calculation of the value of the electric field on the surface of the conduc... more This paper presents a calculation of the value of the electric field on the surface of the conductors and in the immediate vicinity of the high voltage transmission line of 400 kV level. For the calculation of the values of the electric field, the CSM method is used. Verifying the established model was carried out by comparing the calculation results with results of measurements of the electric field at a height of 1 m above ground level. Measurements of the value of electric field lines below the height of 1 m above ground were carried out over the years in Bosnia and Herzegovina. The measurements and calculations were carried out on 400 kV lines of standard dimensions and reduced dimensions. Using the established model, values of the electric field on the surface of the conductors and in their immediate vicinity were calculated. The calculated values of the electric fields are used to determine the corona onset voltage gradients.
Tehnicki vjesnik - Technical Gazette
The safety of managing the electric power system (EPS) in free, deregulated electricity market so... more The safety of managing the electric power system (EPS) in free, deregulated electricity market solves the problem of techno-economic risks related to operative balancing of the system by taking into consideration one of the ancillary services, that is frequency control and exchange active power (f-P), and contribution of renewable energy sources in a specific surrounding. It is well known that the electricity market derives significant risks for all participants, especially for the transmission system operator (TSO) which is responsible for balancing electricity generation and consumption regardless of their probability, which means they have stochastic nature. Therefore, the main idea is to provide the safety of the system's drive by analysing certain risks related to the problem of balancing the process of electricity generation with the goal: ''maximum safety and minimum risk''. The power trading and ancillary services provision comprise technical and financial risks and therefore require a structured risk management. Focus of this paper is on financial risk management that is important for the system operator faces when providing and using ancillary services for balancing of power system.
Nuclear Technology and Radiation Protection
In this ar ti cle the sum mary of mea sure ment and cal cu la tion val ues of low fre quency elec... more In this ar ti cle the sum mary of mea sure ment and cal cu la tion val ues of low fre quency elec tric field ra di a tion around the high-volt age trans mis sion lines and im pact of the in creased volt age val ues on the AC co rona on set volt age gra di ent are pre sented. The mea sure ments of the low fre quency elec tric field ra di a tion level were per formed un der the 400 kV trans mis sion lines of hor i zon tal con fig u ra tion with stan dard and com pact di men sions. In all cases an a lyzed in this ar ti cle, the mea sure ments are per formed in the mid dle of the span, be cause at this point the con duc tors are clos est to the ground. The anal y sis in this ar ti cle has been ini ti ated by the increased volt age val ues of long du ra tion that have been reg is tered in nodes of the 400 kV network in Bosnia and Herzegovina and the neigh bour ing coun tries dur ing the last years. The cal cu la tion of the low fre quency elec tric field ra di a tion of the dif fer ent con fig u ra tion of the high-volt age trans mis sion lines will be use ful for de ter min ing the non-ion iza tion ra di a tion ex po sure lev els of the gen eral pub lic in the fu ture as well as to de ter mine their im pact on the AC co rona on set volt age gra di ent.
Nuclear Technology and Radiation Protection
The paper discusses the possibility of improving the character of gas surge arresters. Examined w... more The paper discusses the possibility of improving the character of gas surge arresters. Examined were: the magnetic field effect, the effect of the hollow cathode, and the effect of the alpha radiation source 241Am. Numerical and real experiments conducted are presented together with theoretical interpretations of the obtained results. Real experiments were carried out on a model of a gas surge arrester spatially constructed for experiments presented in this paper. The model was designed in such a way that it was possible to change all the relevant parameters of the gas surge arrester model. Experiments were conducted under well-controlled laboratory conditions. The tests were performed with d. c. and impulse voltage. The results obtained by experiments were processed by sophisticated statistical methods. The expressed measurement uncertainty of the experimental procedure showed a high statistical reliability of the obtained results. Based on the results of the research, the model of...
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Papers by Zijad Bajramovic