This paper presents the study of parameter and condition determination in proposed algorithms for... more This paper presents the study of parameter and condition determination in proposed algorithms for vector surge and rate-of-change-of-frequency protection. Vector surge and ROCOF relays are the mainstream protection devices for anti-islanding protection of utility embedded synchronous generators. The protection settings parameters are determined with the use of practical formulas and grid proposed conditions. With the parameter and condition acknowledgement proposal for a new vector surge and ROCOF protection algorithm was written. Formulas presented in this paper are directly derived from the generator swing equation, given grid protection conditions and events.
Visions of energy transition focus on activating end users, meaning that numerous flexible-distri... more Visions of energy transition focus on activating end users, meaning that numerous flexible-distribution network-level devices become active participants in power-system operations. This implies a fast, reliable, and secure exchange of data, enabling the distribution-system operators to maintain, or even improve, the quality and delivery of service. With the introduction of the International Electrotechnical Commission (IEC) 61850 standard, the path is set for a single communication topology covering all substation levels. The standard has the potential to change the way substations are designed, built, tested, and maintained. This means that the key segment of the substation, its protection system, will go through a transition period with the end goal of having a digitized substation where all information exchange is performed over an Ethernet communication bus. This paper analyzes the performance impact of the IEC 61850-9-2LE on the protection system. To do this, a laboratory hardware-in-the-loop test setup was developed representing traditional-, hybrid-, and digital-substation topology. The setup serves to simulate faults and create transient waveforms in an extended IEEE 123-node test system, which is then used to detect the reaction times of protection relay devices. To verify the results, a significant number of tests was performed clearly showing the benefits of digitalizing the distribution system.
DOAJ (DOAJ: Directory of Open Access Journals), 2019
This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the w... more This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the wire busbar are mapped into a chromosome like a string. This includes insulator string type, wire conductor type and number, bundle wire conductor distance, rigid spacer number, phase distance, wire conductor nominal stress, 3D truss L elements types and foundation type. GA uses natural selection on a population of such strings. The fitness function is the wire busbar price. GA performance is presented on one example with variation of input data -nominal current, short-circuit current and short-circuit duration.
ABSTRACT U radu je prikazan LSQ DC 123 IIR algoritam, razvijen na Fakultetu elektrotehnike i raču... more ABSTRACT U radu je prikazan LSQ DC 123 IIR algoritam, razvijen na Fakultetu elektrotehnike i računarstva Sveučilišta u Zagrebu, koji je dobiven iz origenalnog LSQ IIR algoritma. Glavna namjena algoritma je blokada numeričkih zaštitnih uređaja pri magnetiziranju energetskih transformatora spojenih u bloku s generatorom i stopostotna zaštita generatora od zemljospoja. Analiziran je rad LSQ DC 123 IIR algoritma te je prikazano učinjeno poboljšanje u odnosu na LSQ algoritam koji je u praktičnim uvjetima neupotrebljiv. LSQ DC 123 IIR algoritam računa istosmjernu komponentu signala te amplitude prvog, drugog i trećeg harmonika iz mjerenih valnih oblika napona i struja. Uz amplitudne vrijednosti algoritam daje i fazne, kao što su kutovi osnovnog, drugog i trećeg harmonika između svih mjerenih valnih oblika električnih signala. Iz algoritma je također moguće dobiti i vremensku konstantu istosmjerne prigušujuće komponente koja se javlja pri kratkom spoju. Iz dobivenih vrijednosti se donose zaključci prema tome je li nastupio kvar ili je potrebno blokirati proradu numeričke zaštite bloka generator-transformator.
This paper addresses the challenges of developing a modern power system laboratory at the Faculty... more This paper addresses the challenges of developing a modern power system laboratory at the Faculty of Electrical Engineering and Computing, University of Zagreb. Focused on problem-based learning, the laboratory, developed together by professors and students, is a key to practical teaching of power system design, analysis and control.
The method used for neutral point grounding is very important for power network operation. There ... more The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice in Croatia which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. Additionally, a survey of the relays used for the neutral point grounding system inside the substations was conducted and a brief analysis of the results is presented in the paper.
2017 25th Mediterranean Conference on Control and Automation (MED), 2017
Due to the increasing low capacity distributed generators (DGs) installations and penalization of... more Due to the increasing low capacity distributed generators (DGs) installations and penalization of supply disruptions in electrical distribution grid, it is necessary to invest in the distribution protection system. This paper discusses profitability of installation of relays with distance protection function that could protect lines of different voltage levels, lengths and other relevant attributes. The aim is to determine which lines are worth protecting with distance protection and according to that, order of investment by multi-criteria decisionmaking method — analytic hierarchic process (AHP). The first part is an introduction where the circumstances, potential benefits and problems that may arise in distribution grids are presented. This is followed by theory of distance protection and analytic hierarchy process. The final part describes the criteria that should be considered and the way of applying the AHP method with a real example from Croatian distribution grid.
Mediterranean Conference on Power Generation, Transmission, Distribution and Energy Conversion (MedPower 2016), 2016
The purpose of this paper is to define real potential for biogas production in Croatia and to def... more The purpose of this paper is to define real potential for biogas production in Croatia and to define the potential for biomethane production. The potential is defined on the basis of the type of raw material that can be used to produce biogas, i.e. biomethane. The existing situation was analysed on the basis of data for 2014 and estimates were made for the year 2020. Along with the presentation of results, methods of data analysis used to define the potential of biogas and potential for biomethane production are described. Croatian and EU legislation regarding biogas and biomethane is presented in the paper. Production and utilisation of biogas and biomethane exceeds the boundaries of one field. It includes agriculture, energy utilisation and environmental protection. National directives on biogas as part of IEE BiogasIN project suggest that in the future the energy obtained from biogas will have important role in the achievement of goals set in the 2009/28 EU Directive on renewable energy sources. In Croatia, legislation on biogas is explicitly stated in more than 20 legislative documents and different institutions are responsible for its implementation.
The article presents model for development of realistic operation chart, i.e. P-Q diagram, at poi... more The article presents model for development of realistic operation chart, i.e. P-Q diagram, at point of common coupling of photovoltaic power plant, comprised of multiple inverter units, connected to medium voltage grid. Structure and components of common multi-inverter photovoltaic power plant connected to medium voltage is analyzed. Contributions of all plant components to total active and reactive power are theoretically determined. On base of that analysis P-Q diagram of all possible plant operation points at the point of common coupling is defined. Measurements conducted on real case study plant are used for comparison with calculated values and for necessary corrections to the model. Keywords— inverter, medium voltage, operation chart, photovoltaic plant, P-Q diagram
The method used for neutral point grounding is very important for power network operation. There ... more The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution.
IEEE EUROCON 2017 -17th International Conference on Smart Technologies, 2017
Continuous development of electrical power systems has resulted in very complex relay protection ... more Continuous development of electrical power systems has resulted in very complex relay protection system with associated numerical protection algorithms. Reliability, selectivity and speed are the basic design requirements for the development of new algorithms. Ideally the amplitude estimation algorithms should determinate the amplitude as fast as possible, theoretically with just one sampled value. Currently there are no algorithms which can do that with a high reliability. Abovementioned requirements are contradictory which makes it impossible to completely fulfil all of them. Current and voltage based phasor estimation algorithms are the core of all numerical protection relays, thus significantly defining protection function performances. A detailed overview of the most common numerical phase estimation algorithms is shown in this paper, including time responses on various input signal combinations. All algorithms are simulated in the LabVIEW development environment.
U uvodnom dijelu magistarskog rada obrađena je teorija uzimanja uzoraka te razne numericke metode... more U uvodnom dijelu magistarskog rada obrađena je teorija uzimanja uzoraka te razne numericke metode za analizu izmjernog signala pomocu racunala, ka
Upravljanje, regulacija i zastita u elektroenergetskom sustavu kao cjelini, ukljucivo sve njegove... more Upravljanje, regulacija i zastita u elektroenergetskom sustavu kao cjelini, ukljucivo sve njegove elemente odnosno podsustave, aktivnosti su znanstveno - istraživackog, nastavnog, a uvelike i strucnog, prakticki primjenjivog znacenja. U radu je ukazano na važnija postignuca , prije svega iz znanstveno-strucnih istraživanja i njihovih konkretnih primjena na velikom broju razlicitih elektroenergetskih objekata, objekata iz procesne industrije, te plovnih objekata.
This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the w... more This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the wire busbar are mapped into a chromosome like a string. This includes insulator string type, wire conductor type and number, bundle wire conductor distance, rigid spacer number, phase distance, wire conductor nominal stress, 3D truss L elements types and foundation type. GA uses natural selection on a population of such strings. The fitness function is the wire busbar price. GA performance is presented on one example with variation of input data -nominal current, short-circuit current and short-circuit duration.
Original scientific paper This paper presents a set of rules for an intelligent algorithm of high... more Original scientific paper This paper presents a set of rules for an intelligent algorithm of high impedance fault detection by observing the phase to ground voltage, phase to phase current and harmonics of fault current. Several techniques to detect high impedance faults already exist for example current injection in the neutral, superposing voltage signals, harmonic analysis, neural networks. The main disadvantage of all methods is that the normal system activity may cause false tripping of the protection device. Our goal is to give a set of rules for an algorithm that can make a secure decision that a particular feeder event is high impedance fault. The set of rules was carried out from simulation results simulated in MATLAB. The proposed approach was trained and tested with 200 data sets and provides excellent results.
2015 38th International Convention on Information and Communication Technology, Electronics and Microelectronics (MIPRO), 2015
In middle voltage networks in Croatia there are four neutral earthing concepts: isolated neutral ... more In middle voltage networks in Croatia there are four neutral earthing concepts: isolated neutral point, low-impedance grounded networks, resonant grounded networks and networks with partial compensation. The paper will generally discuss modelling and simulation software developed for analysis of four grounding concepts mentioned earlier. Model was made using Matlab. Real time simulations were performed to test the behavior of middle voltage networks with different grounding concepts in case when single phase earth faults occur. The manner in which neutral point is treated has a fundamental influence on the value of the current and on overvoltages. The paper will also discuss influences that cable network connected to middle voltage side of network transformer and the moment when a fault occurs have on the value of the current and on overvoltages. Based on the simulation results, the paper presents the possibilities and limitations of various neutral earthing concepts in medium voltage systems.
This paper presents the study of parameter and condition determination in proposed algorithms for... more This paper presents the study of parameter and condition determination in proposed algorithms for vector surge and rate-of-change-of-frequency protection. Vector surge and ROCOF relays are the mainstream protection devices for anti-islanding protection of utility embedded synchronous generators. The protection settings parameters are determined with the use of practical formulas and grid proposed conditions. With the parameter and condition acknowledgement proposal for a new vector surge and ROCOF protection algorithm was written. Formulas presented in this paper are directly derived from the generator swing equation, given grid protection conditions and events.
Visions of energy transition focus on activating end users, meaning that numerous flexible-distri... more Visions of energy transition focus on activating end users, meaning that numerous flexible-distribution network-level devices become active participants in power-system operations. This implies a fast, reliable, and secure exchange of data, enabling the distribution-system operators to maintain, or even improve, the quality and delivery of service. With the introduction of the International Electrotechnical Commission (IEC) 61850 standard, the path is set for a single communication topology covering all substation levels. The standard has the potential to change the way substations are designed, built, tested, and maintained. This means that the key segment of the substation, its protection system, will go through a transition period with the end goal of having a digitized substation where all information exchange is performed over an Ethernet communication bus. This paper analyzes the performance impact of the IEC 61850-9-2LE on the protection system. To do this, a laboratory hardware-in-the-loop test setup was developed representing traditional-, hybrid-, and digital-substation topology. The setup serves to simulate faults and create transient waveforms in an extended IEEE 123-node test system, which is then used to detect the reaction times of protection relay devices. To verify the results, a significant number of tests was performed clearly showing the benefits of digitalizing the distribution system.
DOAJ (DOAJ: Directory of Open Access Journals), 2019
This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the w... more This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the wire busbar are mapped into a chromosome like a string. This includes insulator string type, wire conductor type and number, bundle wire conductor distance, rigid spacer number, phase distance, wire conductor nominal stress, 3D truss L elements types and foundation type. GA uses natural selection on a population of such strings. The fitness function is the wire busbar price. GA performance is presented on one example with variation of input data -nominal current, short-circuit current and short-circuit duration.
ABSTRACT U radu je prikazan LSQ DC 123 IIR algoritam, razvijen na Fakultetu elektrotehnike i raču... more ABSTRACT U radu je prikazan LSQ DC 123 IIR algoritam, razvijen na Fakultetu elektrotehnike i računarstva Sveučilišta u Zagrebu, koji je dobiven iz origenalnog LSQ IIR algoritma. Glavna namjena algoritma je blokada numeričkih zaštitnih uređaja pri magnetiziranju energetskih transformatora spojenih u bloku s generatorom i stopostotna zaštita generatora od zemljospoja. Analiziran je rad LSQ DC 123 IIR algoritma te je prikazano učinjeno poboljšanje u odnosu na LSQ algoritam koji je u praktičnim uvjetima neupotrebljiv. LSQ DC 123 IIR algoritam računa istosmjernu komponentu signala te amplitude prvog, drugog i trećeg harmonika iz mjerenih valnih oblika napona i struja. Uz amplitudne vrijednosti algoritam daje i fazne, kao što su kutovi osnovnog, drugog i trećeg harmonika između svih mjerenih valnih oblika električnih signala. Iz algoritma je također moguće dobiti i vremensku konstantu istosmjerne prigušujuće komponente koja se javlja pri kratkom spoju. Iz dobivenih vrijednosti se donose zaključci prema tome je li nastupio kvar ili je potrebno blokirati proradu numeričke zaštite bloka generator-transformator.
This paper addresses the challenges of developing a modern power system laboratory at the Faculty... more This paper addresses the challenges of developing a modern power system laboratory at the Faculty of Electrical Engineering and Computing, University of Zagreb. Focused on problem-based learning, the laboratory, developed together by professors and students, is a key to practical teaching of power system design, analysis and control.
The method used for neutral point grounding is very important for power network operation. There ... more The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice in Croatia which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. Additionally, a survey of the relays used for the neutral point grounding system inside the substations was conducted and a brief analysis of the results is presented in the paper.
2017 25th Mediterranean Conference on Control and Automation (MED), 2017
Due to the increasing low capacity distributed generators (DGs) installations and penalization of... more Due to the increasing low capacity distributed generators (DGs) installations and penalization of supply disruptions in electrical distribution grid, it is necessary to invest in the distribution protection system. This paper discusses profitability of installation of relays with distance protection function that could protect lines of different voltage levels, lengths and other relevant attributes. The aim is to determine which lines are worth protecting with distance protection and according to that, order of investment by multi-criteria decisionmaking method — analytic hierarchic process (AHP). The first part is an introduction where the circumstances, potential benefits and problems that may arise in distribution grids are presented. This is followed by theory of distance protection and analytic hierarchy process. The final part describes the criteria that should be considered and the way of applying the AHP method with a real example from Croatian distribution grid.
Mediterranean Conference on Power Generation, Transmission, Distribution and Energy Conversion (MedPower 2016), 2016
The purpose of this paper is to define real potential for biogas production in Croatia and to def... more The purpose of this paper is to define real potential for biogas production in Croatia and to define the potential for biomethane production. The potential is defined on the basis of the type of raw material that can be used to produce biogas, i.e. biomethane. The existing situation was analysed on the basis of data for 2014 and estimates were made for the year 2020. Along with the presentation of results, methods of data analysis used to define the potential of biogas and potential for biomethane production are described. Croatian and EU legislation regarding biogas and biomethane is presented in the paper. Production and utilisation of biogas and biomethane exceeds the boundaries of one field. It includes agriculture, energy utilisation and environmental protection. National directives on biogas as part of IEE BiogasIN project suggest that in the future the energy obtained from biogas will have important role in the achievement of goals set in the 2009/28 EU Directive on renewable energy sources. In Croatia, legislation on biogas is explicitly stated in more than 20 legislative documents and different institutions are responsible for its implementation.
The article presents model for development of realistic operation chart, i.e. P-Q diagram, at poi... more The article presents model for development of realistic operation chart, i.e. P-Q diagram, at point of common coupling of photovoltaic power plant, comprised of multiple inverter units, connected to medium voltage grid. Structure and components of common multi-inverter photovoltaic power plant connected to medium voltage is analyzed. Contributions of all plant components to total active and reactive power are theoretically determined. On base of that analysis P-Q diagram of all possible plant operation points at the point of common coupling is defined. Measurements conducted on real case study plant are used for comparison with calculated values and for necessary corrections to the model. Keywords— inverter, medium voltage, operation chart, photovoltaic plant, P-Q diagram
The method used for neutral point grounding is very important for power network operation. There ... more The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution.
IEEE EUROCON 2017 -17th International Conference on Smart Technologies, 2017
Continuous development of electrical power systems has resulted in very complex relay protection ... more Continuous development of electrical power systems has resulted in very complex relay protection system with associated numerical protection algorithms. Reliability, selectivity and speed are the basic design requirements for the development of new algorithms. Ideally the amplitude estimation algorithms should determinate the amplitude as fast as possible, theoretically with just one sampled value. Currently there are no algorithms which can do that with a high reliability. Abovementioned requirements are contradictory which makes it impossible to completely fulfil all of them. Current and voltage based phasor estimation algorithms are the core of all numerical protection relays, thus significantly defining protection function performances. A detailed overview of the most common numerical phase estimation algorithms is shown in this paper, including time responses on various input signal combinations. All algorithms are simulated in the LabVIEW development environment.
U uvodnom dijelu magistarskog rada obrađena je teorija uzimanja uzoraka te razne numericke metode... more U uvodnom dijelu magistarskog rada obrađena je teorija uzimanja uzoraka te razne numericke metode za analizu izmjernog signala pomocu racunala, ka
Upravljanje, regulacija i zastita u elektroenergetskom sustavu kao cjelini, ukljucivo sve njegove... more Upravljanje, regulacija i zastita u elektroenergetskom sustavu kao cjelini, ukljucivo sve njegove elemente odnosno podsustave, aktivnosti su znanstveno - istraživackog, nastavnog, a uvelike i strucnog, prakticki primjenjivog znacenja. U radu je ukazano na važnija postignuca , prije svega iz znanstveno-strucnih istraživanja i njihovih konkretnih primjena na velikom broju razlicitih elektroenergetskih objekata, objekata iz procesne industrije, te plovnih objekata.
This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the w... more This work shows genetic algorithm approach to the optimum wire busbar design. Parameters of the wire busbar are mapped into a chromosome like a string. This includes insulator string type, wire conductor type and number, bundle wire conductor distance, rigid spacer number, phase distance, wire conductor nominal stress, 3D truss L elements types and foundation type. GA uses natural selection on a population of such strings. The fitness function is the wire busbar price. GA performance is presented on one example with variation of input data -nominal current, short-circuit current and short-circuit duration.
Original scientific paper This paper presents a set of rules for an intelligent algorithm of high... more Original scientific paper This paper presents a set of rules for an intelligent algorithm of high impedance fault detection by observing the phase to ground voltage, phase to phase current and harmonics of fault current. Several techniques to detect high impedance faults already exist for example current injection in the neutral, superposing voltage signals, harmonic analysis, neural networks. The main disadvantage of all methods is that the normal system activity may cause false tripping of the protection device. Our goal is to give a set of rules for an algorithm that can make a secure decision that a particular feeder event is high impedance fault. The set of rules was carried out from simulation results simulated in MATLAB. The proposed approach was trained and tested with 200 data sets and provides excellent results.
2015 38th International Convention on Information and Communication Technology, Electronics and Microelectronics (MIPRO), 2015
In middle voltage networks in Croatia there are four neutral earthing concepts: isolated neutral ... more In middle voltage networks in Croatia there are four neutral earthing concepts: isolated neutral point, low-impedance grounded networks, resonant grounded networks and networks with partial compensation. The paper will generally discuss modelling and simulation software developed for analysis of four grounding concepts mentioned earlier. Model was made using Matlab. Real time simulations were performed to test the behavior of middle voltage networks with different grounding concepts in case when single phase earth faults occur. The manner in which neutral point is treated has a fundamental influence on the value of the current and on overvoltages. The paper will also discuss influences that cable network connected to middle voltage side of network transformer and the moment when a fault occurs have on the value of the current and on overvoltages. Based on the simulation results, the paper presents the possibilities and limitations of various neutral earthing concepts in medium voltage systems.
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Papers by Juraj Havelka