ANALYSIS OF SURGE ARRESTERS FAILURES IN THE INSTALLATION OF BROADCASTING TRANSMITTER

In the operation of the broadcasting transmitter, during a lightning storm, comes to frequent surge arrester failures in the switchgear of the broadcasting transmitter and along the 10 kV supply cable (surge arresters in the cable section boxes). Analysis of lightning strokes to the broadcasting transmitter is given in the paper. EMTP simulation of surge arresters loading was conducted. The energy overload of surge arresters is due to lightning flash with more than one lightning strokes or more lightning flashes in short time. Recommendations were also given for improvement of existing surge protection and reduction the number of surge arresters failures

SOLVING EMC PROBLEMS IN THE DESIGN OF NEW HV TEST LABORATORY

The paper deals with solving electromagnetic compatibility (EMC) problems in the design of a new, case study, industrial high voltage test laboratory, intended to be used for testing of transformers and other apparatus up to 550 kV rated voltage. Modern high voltage test facilities are equipped, apart from primary test devices like AC, DC and impulse voltage generators etc., also with sophisticated numerical measuring instruments and informatics technology. Since such devices are sensitive to transient overvoltages, the highest degree of EMC is to be secured. This can be achieved by proper earthing and screening of test laboratory, what shall be designed in a way to satisfy all requirements conditioned by building lightning protection, personal protection and system earthing, avoiding electromagnetic compatibility disturbances at the same time. One of the main tasks is solving electromagnetic compatibility problems caused by outdoor electromagnetic disturbances originating from various unknown sources. Those disturbances and interferences may seriously influence measuring accuracy and readings of test devices, what consequently leads to false results. The stated is especially relating to partial discharge measurements. As to avoid such disturbances, the laboratory shall be completely screened with a net forming optimally designed Faraday cage. On the other hand, at high voltage tests with impulse voltages, especially with chopped tail waves, steep transient overvoltages may be generated. As a consequence, high transient potential differences between particular points along the earth electrode may occur, what can even lead to flashovers between parts of it. Therefore is of utmost importance to provide proper earthing and low inductance current return path for impulse high voltage test equipment where high frequency transients are to be anticipated. Improper earthing and bonding may result, apart from mentioned flashovers, in severe induced voltages in secondary cables with consequential influence on test results, possible destruction of measuring instruments and hazardous touch voltages for personnel. For analyzing transient potential differences, it is important to model, with maximum accuracy, impulse test circuit (impulse generator, chopping spark gap, voltage divider, Faraday cage, fundament earth electrode, earthing strips, earthing rods etc.). Magnitude of transient potential difference between particular points is proportional to earth electrode inductance, i.e. low inductance of earth electrode will result in decrease of transient potential difference

Transients Caused by Sequential Circuit Breaker Tripping Issued by Busbar Protection

A study of transients in a high voltage substation 400/110 kV is presented in the paper. An analysis was carried out after a fault on the 110 kV busbar, which caused severe damage in the substation. Investigation was focused on a time frame of several sequential circuit breaker trippings. A first step of the study was collection of data from the primary and secondary system in the substation and the control centre. After numerous analyses of data an attempt was made to construct a precision model, which could be used in the computation. Appropriate models were developed for circuit breakers, voltage (potential) and current metering transformers, power transformers, surge arresters, overhead lines and an equivalent grid. The components of the power system can be modelled for the very particular purpose, which means that a different frequency model should be used and each element in this analysis has a specific frequency response. An attempt was made at very detailed modelling of a power transformer, air blast and SF6 circuit breakers. Computed results of fault currents were compared with measurements captured by the disturbance recorders in the field, mainly in differential numerical relays. Different switching schemes and different tripping sequences of several 110 kV circuit breakers were analysed with a constructed model in the millisecond range. Models of circuit breaker with different types of media, air blast and SF6 gas were used in the cases investigated. Modelling of the circuit breakers’ electrical arc was an important item in all cases in order to take into account the interaction between electrical arc and circuit current during the process of current interruption. The Schwarz/Avdonin equation is applied to model the dynamic behaviour of an electric arc. The fault studied was accompanied by a large short circuit current. For this particular case two types of circuit breaker, air blast and SF 6 were modelled. An important conclusion from those analyses was that sequential tripping of several circuit breakers does not cause superposition of overvoltages, because interruption the current happens when it is passing through the zero. Even the record from the substation and the disturbances recorder proves that each particular circuit breaker was successfully opened. On that basis, focus was put only on the final opening of the breaker and its arc extinction. The conclusion can be drawn that such a substation fault should have no influence on excessive overvoltages that can threaten the insulation of components in the substation

Design and testing of 25 kV AC electric railway power supply systems

U članku su opisani potrebni koraci za konstruiranje i testiranje novoizgrađene elektrovučne podstanice koja je predviđena za napajanje jednog dijela prigradske pruge u željezničkom čvoru Zagreb. Potrebna snaga za napajanje elektrovučne podstanice određena je na osnovi elektrovučnog proračuna provedenog za maksimalni vozni red. Za vrijeme testnog rada elektrovučne podstanice su provedena potrebna mjerenja da bi se odredile tehničke karakteristike podstanice kao i utjecaj na okolinu. Provedena su i mjerenja kvalitete električne energije na prijenosnoj elektroenergetskoj mreži za vrijeme testnog rada podstanice. Također su dani rezultati mjerenja elektromagnetskog polja unutar i u blizini same podstanice.The paper describes the procedures implemented in the design and testing of the newly built traction substation, which is foreseen for the power supply of part of the electrical tracks in the area of Zagreb. The power capacity of the new traction transformer substation was determined according to the load flow calculation that was carried out for the period of maximal traffic time-table. During the period of test operation a number of measurements were conducted in order to testify technical performances of the substation, as well as to verify its impacts on the environment. Measurements of the power quality in the utility power network, which supplies the traction system, were conducted. Also, measurements of electrical and magnetic fields inside the traction substation and in its vicinity were undertaken

Prenaponi strmog čela u sekundarnim krugovima visokonaponskih rasklopnih postrojenja

Problematika utjecaja primarne opreme visokonaponskih rasklopnih postrojenja te prirodnih elektromagnetskih fenomena na sekundarnu opremu može se obuhvatiti općenitim pojmom kao problematika elektromagnetske kompatibilnosti u postrojenjima elektroenergetskog sustava. Najznačajniji aspekt te problematike su prenaponi strmog čela u sekundarnim krugovima. Nakon uvodnog dijela, u drugom dijelu su date osnovne definicije i klasifikacije prema IEC-u. U trećem dijelu rada prikazana je problematika prenapona u sekundarnim krugovima visokonaponskih rasklopnih postrojenja. Tu su detaljno rasčlanjeni atmosferski utjecaji i sklopne manipulacije. Također, u tom poglavlju su detaljno obrađeni mehanizmi prijenosa između izvora smetnje i prijemnika posebno kod klasičnih a posebno kod plinom izoliranih rasklopnih postrojenja. Koncept zaštitnih zona u zaštiti od munje kao mjera za postizanje željene elektromagnetske kompatibilnosti prikazan je u četvrtom poglavlju. Primjena takvog koncepta te nužnost interdisciplinarnog rada svih učesnika u projektu također je objašnjena u tom poglavlju. U petom poglavlju su prikazana dva računalna programa za simulaciju udara munje. Dati su matematički modeli koji su implementirani u programe te su također rezultati simulacije uspoređeni na konkretnom rasklopnom postrojenju. Rezultati simulacije iz prethodnog poglavlja korišteni su u šestom poglavlju kao ulazni podaci za proračun tranzijentnih porasta potencijala uzemljivača. U ovom poglavlju je prikazan samo mali dio proračuna koji su urađeni. U sedmom poglavlju su prikazane obuhvatne zaštitne mjere koje su rasčlanjene na mjere protiv nastanka uzdužnog i poprečnog napona. U tom poglavlju su, između ostalog, prikazani zaštitni elementi koji se mogu koristit kao dodatne zaštitne mjere na sekundarnoj strani. Za neke od tih elemenata snimljeni su i odzivi pri nailasku prenapona strmog čela. U zaključku su date najvažnije smjernice pri gradnji novih i rekonstrukciji postojećih visokonaponskih postrojenja koje su proizišle kao rezultat rada na problematici prenapona strmog čela u sekundarnim krugovima.Influence problems of primary equipment of high voltage switchgear and natural electromagnetic phenomena on secondary equipment can be clasped with general notion like electromagnetic compatibility problems in switchgear of electricity system. The most important fact of that problem are fast and very fast overvoltages in secondary (low voltage) circuits. After introduction part, in second part were given fundamental definitions and classes according to IEC norms. In third part were presented overvoltage problems in low voltage circuits of high voltage switchgear. In this part were detail divided lightning influence and switching operation influence. Also, in this part were detail described transfer mechanisms between source of disturbance and receiver of disturbance by classic switchgear and by gas insulated switchgear. Concept of protection area in lightning protection, like measure of electromagnetic compatibility, was presented in fourth part. Application of that concept and necessity of interdisciplinary work of all members in project was also explained in this part. In fifth part were presented two computer programs for lightning stroke simulation. In this part was also given mathematics models, which were implemented in programs. Results were also compared on concrete switchgear. Results of simulations from preliminary part were used in sixth part like introduction data for calculation of transient potential rise of grounding grid. In this part was presented only a little piece of calculation, which were made. In seventh part were presented encircle protection measures. These were divided into measures against common-mode voltage and measures against line to ground voltage. In this part were presented, between others, protection element that can be used like addition protection measures on second side (in low voltage circuits). For certain of those elements were recorded responses on fast-front overvoltages. In conclusion were given the most important directions by building of new and reconstruction of existing high voltage switchgear. These directions are results of work on problems of fast-front overvoltages in secondary low voltage circuits

Method of Surge Protective Devices Selection in Low-Voltage Systems

U disertaciji su najprije objašnjeni osnovni pojmovi te stanje prenaponske zaštite na niskom naponu i cilj rada. Zatim je objašnjeno nastajanje i djelovanje prenapona, gromobranska zaštita, uređaji prenaponske zaštite te prenaponska zaštita prema IEC normama. Parametri struje munje za različite klase gromobranske zaštite su implicirali uvođenje valnog oblika za ispitivanje uređaja prenaponske zaštite. Modeli za simulaciju energetskog opterećenja uređaja prenaponske zaštite detaljno su izloženi u trećem poglavlju. Karakteristike pojedinih elemenata modela su određene laboratorijskim ispitivanjima. Proveden je izbor parametara struje munje uzimajući u obzir vjerojatnost pojave struje određene amplitude i vremena trajanja. Detaljno su prikazani rezultati simulacija energetskog opterećenja uređaja prenaponske zaštite u NN mreži. Provedena je i analiza osjetljivosti modela na ulazne parametre. Simulacijama je pokazano da inducirani prenaponi ne mogu značajno energetski opteretiti uređaje prenaponske zaštite. Zaštitna udaljenost uređaja prenaponske zaštite je istraživana na posebnom modelu. Zaključak disertacije ističe, uvođenjem prihvatljivog rizika energetskog preopterećenja uređaja prenaponske zaštite može se riješiti nesuglasje oko valnog oblika za ispitivanja. Disertacija sadrži i popis literature zatim popis skraćenica, oznaka, slika i tablica, zatim četiri priloga, sažetak na hrvatskom i engleskom jeziku te životopis na hrvatskom i engleskom jeziku.In dissertation, capital technical data are first explained, as well as the state of low-voltage surge protection and aim of dissertation. Afterwards are explained the origin and surge effect, lightning protection system, surge protective devices and surge protection according to IEC standards. The lightning current parameters for the different classes of lightning protection are implicated introduction of current wave shape for SPD testing. Models for simulation of SPD energy absorption are laid out in-depth in the third paragraph. Characteristics of single model elements are estimated by laboratory testing. Choices of lightning current parameters are performed, taking in account probability of lightning current amplitude and duration of lightning wave. The results of simulation of SPDs energy absorption in low-voltage line are shown in-depth. Sensitivity of model on calculation parameters is also analyzed. Simulation of induced overvoltages are shown, induced overvoltages cannot load SPDs with high energy. Protective distance of SPD is researched on special model. Conclusion of dissertation is pointed out; introduction of acceptable risk of SPD energy overloading can be solution for discrepancy about current wave shape for SPD testing. Dissertation includes also list of references, list of abbreviations and marks, list of pictures and tables, four supplements, summary and biography in Croatian and English

Prenaponi strmog čela u sekundarnim krugovima visokonaponskih rasklopnih postrojenja

Problematika utjecaja primarne opreme visokonaponskih rasklopnih postrojenja te prirodnih elektromagnetskih fenomena na sekundarnu opremu može se obuhvatiti općenitim pojmom kao problematika elektromagnetske kompatibilnosti u postrojenjima elektroenergetskog sustava. Najznačajniji aspekt te problematike su prenaponi strmog čela u sekundarnim krugovima. Nakon uvodnog dijela, u drugom dijelu su date osnovne definicije i klasifikacije prema IEC-u. U trećem dijelu rada prikazana je problematika prenapona u sekundarnim krugovima visokonaponskih rasklopnih postrojenja. Tu su detaljno rasčlanjeni atmosferski utjecaji i sklopne manipulacije. Također, u tom poglavlju su detaljno obrađeni mehanizmi prijenosa između izvora smetnje i prijemnika posebno kod klasičnih a posebno kod plinom izoliranih rasklopnih postrojenja. Koncept zaštitnih zona u zaštiti od munje kao mjera za postizanje željene elektromagnetske kompatibilnosti prikazan je u četvrtom poglavlju. Primjena takvog koncepta te nužnost interdisciplinarnog rada svih učesnika u projektu također je objašnjena u tom poglavlju. U petom poglavlju su prikazana dva računalna programa za simulaciju udara munje. Dati su matematički modeli koji su implementirani u programe te su također rezultati simulacije uspoređeni na konkretnom rasklopnom postrojenju. Rezultati simulacije iz prethodnog poglavlja korišteni su u šestom poglavlju kao ulazni podaci za proračun tranzijentnih porasta potencijala uzemljivača. U ovom poglavlju je prikazan samo mali dio proračuna koji su urađeni. U sedmom poglavlju su prikazane obuhvatne zaštitne mjere koje su rasčlanjene na mjere protiv nastanka uzdužnog i poprečnog napona. U tom poglavlju su, između ostalog, prikazani zaštitni elementi koji se mogu koristit kao dodatne zaštitne mjere na sekundarnoj strani. Za neke od tih elemenata snimljeni su i odzivi pri nailasku prenapona strmog čela. U zaključku su date najvažnije smjernice pri gradnji novih i rekonstrukciji postojećih visokonaponskih postrojenja koje su proizišle kao rezultat rada na problematici prenapona strmog čela u sekundarnim krugovima.Influence problems of primary equipment of high voltage switchgear and natural electromagnetic phenomena on secondary equipment can be clasped with general notion like electromagnetic compatibility problems in switchgear of electricity system. The most important fact of that problem are fast and very fast overvoltages in secondary (low voltage) circuits. After introduction part, in second part were given fundamental definitions and classes according to IEC norms. In third part were presented overvoltage problems in low voltage circuits of high voltage switchgear. In this part were detail divided lightning influence and switching operation influence. Also, in this part were detail described transfer mechanisms between source of disturbance and receiver of disturbance by classic switchgear and by gas insulated switchgear. Concept of protection area in lightning protection, like measure of electromagnetic compatibility, was presented in fourth part. Application of that concept and necessity of interdisciplinary work of all members in project was also explained in this part. In fifth part were presented two computer programs for lightning stroke simulation. In this part was also given mathematics models, which were implemented in programs. Results were also compared on concrete switchgear. Results of simulations from preliminary part were used in sixth part like introduction data for calculation of transient potential rise of grounding grid. In this part was presented only a little piece of calculation, which were made. In seventh part were presented encircle protection measures. These were divided into measures against common-mode voltage and measures against line to ground voltage. In this part were presented, between others, protection element that can be used like addition protection measures on second side (in low voltage circuits). For certain of those elements were recorded responses on fast-front overvoltages. In conclusion were given the most important directions by building of new and reconstruction of existing high voltage switchgear. These directions are results of work on problems of fast-front overvoltages in secondary low voltage circuits

Method of Surge Protective Devices Selection in Low-Voltage Systems

U disertaciji su najprije objašnjeni osnovni pojmovi te stanje prenaponske zaštite na niskom naponu i cilj rada. Zatim je objašnjeno nastajanje i djelovanje prenapona, gromobranska zaštita, uređaji prenaponske zaštite te prenaponska zaštita prema IEC normama. Parametri struje munje za različite klase gromobranske zaštite su implicirali uvođenje valnog oblika za ispitivanje uređaja prenaponske zaštite. Modeli za simulaciju energetskog opterećenja uređaja prenaponske zaštite detaljno su izloženi u trećem poglavlju. Karakteristike pojedinih elemenata modela su određene laboratorijskim ispitivanjima. Proveden je izbor parametara struje munje uzimajući u obzir vjerojatnost pojave struje određene amplitude i vremena trajanja. Detaljno su prikazani rezultati simulacija energetskog opterećenja uređaja prenaponske zaštite u NN mreži. Provedena je i analiza osjetljivosti modela na ulazne parametre. Simulacijama je pokazano da inducirani prenaponi ne mogu značajno energetski opteretiti uređaje prenaponske zaštite. Zaštitna udaljenost uređaja prenaponske zaštite je istraživana na posebnom modelu. Zaključak disertacije ističe, uvođenjem prihvatljivog rizika energetskog preopterećenja uređaja prenaponske zaštite može se riješiti nesuglasje oko valnog oblika za ispitivanja. Disertacija sadrži i popis literature zatim popis skraćenica, oznaka, slika i tablica, zatim četiri priloga, sažetak na hrvatskom i engleskom jeziku te životopis na hrvatskom i engleskom jeziku.In dissertation, capital technical data are first explained, as well as the state of low-voltage surge protection and aim of dissertation. Afterwards are explained the origin and surge effect, lightning protection system, surge protective devices and surge protection according to IEC standards. The lightning current parameters for the different classes of lightning protection are implicated introduction of current wave shape for SPD testing. Models for simulation of SPD energy absorption are laid out in-depth in the third paragraph. Characteristics of single model elements are estimated by laboratory testing. Choices of lightning current parameters are performed, taking in account probability of lightning current amplitude and duration of lightning wave. The results of simulation of SPDs energy absorption in low-voltage line are shown in-depth. Sensitivity of model on calculation parameters is also analyzed. Simulation of induced overvoltages are shown, induced overvoltages cannot load SPDs with high energy. Protective distance of SPD is researched on special model. Conclusion of dissertation is pointed out; introduction of acceptable risk of SPD energy overloading can be solution for discrepancy about current wave shape for SPD testing. Dissertation includes also list of references, list of abbreviations and marks, list of pictures and tables, four supplements, summary and biography in Croatian and English

Prenaponi strmog čela u sekundarnim krugovima visokonaponskih rasklopnih postrojenja

Problematika utjecaja primarne opreme visokonaponskih rasklopnih postrojenja te prirodnih elektromagnetskih fenomena na sekundarnu opremu može se obuhvatiti općenitim pojmom kao problematika elektromagnetske kompatibilnosti u postrojenjima elektroenergetskog sustava. Najznačajniji aspekt te problematike su prenaponi strmog čela u sekundarnim krugovima. Nakon uvodnog dijela, u drugom dijelu su date osnovne definicije i klasifikacije prema IEC-u. U trećem dijelu rada prikazana je problematika prenapona u sekundarnim krugovima visokonaponskih rasklopnih postrojenja. Tu su detaljno rasčlanjeni atmosferski utjecaji i sklopne manipulacije. Također, u tom poglavlju su detaljno obrađeni mehanizmi prijenosa između izvora smetnje i prijemnika posebno kod klasičnih a posebno kod plinom izoliranih rasklopnih postrojenja. Koncept zaštitnih zona u zaštiti od munje kao mjera za postizanje željene elektromagnetske kompatibilnosti prikazan je u četvrtom poglavlju. Primjena takvog koncepta te nužnost interdisciplinarnog rada svih učesnika u projektu također je objašnjena u tom poglavlju. U petom poglavlju su prikazana dva računalna programa za simulaciju udara munje. Dati su matematički modeli koji su implementirani u programe te su također rezultati simulacije uspoređeni na konkretnom rasklopnom postrojenju. Rezultati simulacije iz prethodnog poglavlja korišteni su u šestom poglavlju kao ulazni podaci za proračun tranzijentnih porasta potencijala uzemljivača. U ovom poglavlju je prikazan samo mali dio proračuna koji su urađeni. U sedmom poglavlju su prikazane obuhvatne zaštitne mjere koje su rasčlanjene na mjere protiv nastanka uzdužnog i poprečnog napona. U tom poglavlju su, između ostalog, prikazani zaštitni elementi koji se mogu koristit kao dodatne zaštitne mjere na sekundarnoj strani. Za neke od tih elemenata snimljeni su i odzivi pri nailasku prenapona strmog čela. U zaključku su date najvažnije smjernice pri gradnji novih i rekonstrukciji postojećih visokonaponskih postrojenja koje su proizišle kao rezultat rada na problematici prenapona strmog čela u sekundarnim krugovima.Influence problems of primary equipment of high voltage switchgear and natural electromagnetic phenomena on secondary equipment can be clasped with general notion like electromagnetic compatibility problems in switchgear of electricity system. The most important fact of that problem are fast and very fast overvoltages in secondary (low voltage) circuits. After introduction part, in second part were given fundamental definitions and classes according to IEC norms. In third part were presented overvoltage problems in low voltage circuits of high voltage switchgear. In this part were detail divided lightning influence and switching operation influence. Also, in this part were detail described transfer mechanisms between source of disturbance and receiver of disturbance by classic switchgear and by gas insulated switchgear. Concept of protection area in lightning protection, like measure of electromagnetic compatibility, was presented in fourth part. Application of that concept and necessity of interdisciplinary work of all members in project was also explained in this part. In fifth part were presented two computer programs for lightning stroke simulation. In this part was also given mathematics models, which were implemented in programs. Results were also compared on concrete switchgear. Results of simulations from preliminary part were used in sixth part like introduction data for calculation of transient potential rise of grounding grid. In this part was presented only a little piece of calculation, which were made. In seventh part were presented encircle protection measures. These were divided into measures against common-mode voltage and measures against line to ground voltage. In this part were presented, between others, protection element that can be used like addition protection measures on second side (in low voltage circuits). For certain of those elements were recorded responses on fast-front overvoltages. In conclusion were given the most important directions by building of new and reconstruction of existing high voltage switchgear. These directions are results of work on problems of fast-front overvoltages in secondary low voltage circuits