Fredrik Carlsson was born in Stockholm, Sweden, on January 17, 1974. He wrote his master thesis in late 1998 in the field of "models of electric actuators for railway vehicles", which was entitled the best master thesis in railway techniques by Swedtrain. He received his M.Sc. degree 1999 in Electrical Engineering from KTH, Royal Institute of Technology in Stockholm, Sweden. He got his Ph.D. degree in January 2004 with the title "On impacts and ride-through of voltage sags exposing line-operated AC-machines". He has then worked as a researcher at the department of Electrical engineering, KTH, Stockholm, Sweden. Research was done in the fields of diagnostics, traction applications, and hybrid vehicles. Since 2008, he is working as a senior R&D engineer at Vattenfall Research & Development, Sweden. He is mainly working within the fields of Smart Grids, asset management, power quality and wind power.
Abstract: Early detection of undesired conditions during the operation of a centrifugal pump has become very important in order to avoid consequential damages, thus outage time and repair costs can be reduced. Faults in centrifugal pumps can be caused through the changes in flow conditions such as cavitation, that lead to impeller degradation and ultimately to the deterioration and breakdown of pump material. In this project the diagnosis of a submersible centrifugal pump is performed, proving that it is possible to detect not only when cavitation is present but also when it starts using the current and power signature analyses of its motor drive as diagnostic tools. Experimental currents and voltages are measured for different operating points of the pump in order to study the correlation between the cavitation phenomena and the power of the motor.
Abstract: Voltage sags and voltage interruptions are huge power quality problems for many industries. Voltage sags cause apart from eventual tripping, large torque peaks, which may cause damage to the shaft or equipment connected to the shaft. This paper illustrates how the stator flux in a synchronous machine changes during voltage sags. These changes result in torque peaks. An analytical time dependent expression of the stator flux during voltage sags explains the behaviour of synchronous machines and why there are high torque and current peaks during voltage sags. Simulations verify the expressions, and illustrate the dependence of torque and current peaks on voltage sag duration and magnitude.
Abstract: Wind power is one of the renewable energy sources in the electricity system that grows most rapid in Sweden. There are however two market challenges that need to be addressed with a higher proportion of wind power â that is variability and predictability. Predictability is important since the spot market Nord Pool Spot requires forecasts of production 12 â 36 hours ahead. The forecast errors must be regulated with regulating power, which is expensive for the actors causing the forecast errors. This paper has investigated a number of scenarios with 10 â 55 TWh of wind power installed in the Swedish system. The focus has been on a base scenario with 10 TWh new wind power consisting of 3,5 GW new wind power and 1,5 GW already installed power, which gives 5 GW. The results show that the costs for the forecast errors will increase as more intermittent production is installed. However, the increase can be limited by for instance trading on intraday market or increase quality of forecasts.
Abstract: To increase energy efficiency, manufacturers have
introduced appliances with lower energy consumption, such
as lamps based on LED and fluorescent light technology,
electronic transformers, dimmers, power electronic
controlled heat pumps, etc. These technologies significantly
reduces the energy consumption, however, as these
technologies is based on fast switching, harmonics are
introduced. Harmonics from each appliance in the
households are added and emitted to the distribution grid
where the distribution transformer is the first receptor. The
harmonics causes increased losses in the distribution
transformer which gives temperature rise and reduced life.
This paper assembles the results of earlier works and
estimates the costs in the distribution grid for electronic
loads.
Abstract: With an increasing amount of wind power in the electricity system, the increased intermittent production need be addressed since varying production sources need to be balanced along with the already existing producers and consumers. Production from existing wind farms have been used to study the current and past variations in Sweden, for both geographical areas and whole Sweden. The variations are usually low; however there are quite many hours with larger variations that might be a challenge to handle in the future whith much more installed wind power. This paper investigates the variations in terms of standard deviation, mean and max values. This is done for several years and with seasonal variations.
Abstract: Failures of network components could significantly affect the reliability of power systems. Component failures are caused by different factors. Analysis of the failure causes has a practical value since the knowledge of failure causes could help power utilities to take remedial actions and determine appropriate method for failure reduction. To understand the causes of component failures an extensive cause analysis was carried out in a project recently performed at the power company, Vattenfall Distribution in Sweden. The project studied a large amount of network component failures recorded by the company during the latest five-yearsâ period. The project analyzed the fault characteristics and root causes for different component categories. The results of the analysis are presented and discussed in the paper.
Abstract: In the first year of the studies in the five-year Master of Science programme in Electrical Engineering at KTH, there is a course named ?Electro project?. The students that take this compulsory course choose between several projects and this paper describes a newly invented project called Free Fall, which practically and theoretically demonstrates in a simple and interesting way important electrical engineering equations for the students. The students study, calculate and build a gondola that first accelerates when it falls freely along a tower from its top and then decelerate with eddy current brakes. The students learn apart from modelling of physical phenomena, mechanical construction, validation, measurements and collaboration within the group as well as with the laboratory staff.
Abstract: A Free Piston Energy Converter (FPEC) is a combination of a linear combustion engine and a linear electrical machine. This type of converter has many potential advantages like high efficiency, low fuel consumption and low emissions, which make it suitable for a series hybrid vehicle. However, the generated power pulsates due to the reciprocating motion of the translator. This paper presents a comparative study on how different generator force profiles affect the electric power pulsations produced by the FPEC. In addition, the influence of these profiles on translator motion and the needed power converter current is investigated. A dynamic free piston model is used for the investigation. Results show that the generator force profile has a major impact on the power pulsation amplitude and peak current demand. Thus the chosen force profile will affect dimensioning of power converter, electrical machine and energy storage. Furthermore, loading the translator heavily in the beginning or end of the stroke seems to affect the peak translator velocity more than evenly distributed load profiles.
Abstract: This paper investigates the electrical machine, which is one of the important parts in the Free Piston Energy Converter (FPEC). In the previous work it was found that one of the best candidate suitable for the FPEC is a Transverse Flux Machine (TFM) due to the very tough requirements on the electrical ma- chine such as a low weight of the translator (movable part in the machine).This paper presents a new concept of a linear TFM in which strong emphasis has been put to achieve a design that is simple to manufacture. Different types of the magnet configurations on the translator have been investigated. It has been found that the buried magnet design suffers from a very high leakage to the nearby poles and is thus not suitable for this type of machine. Another configuration, which has been investigated, is the surface mounted magnet configuration. Analytical models for this configuration have been established. It has been found that the tough requirements, 4kN from a 6kg movable mass, can
Abstract: This paper investigates how the losses in a Free Piston Energy Converter during start, stop and idling affects energy consumption and required power from the supply system. Simulation results indicate that the electrical machine efficiency is the most critical factor during start. Moreover, by choosing the correct amplitude of the starting force, energy consumption during start can be reduced. When it comes to idling, friction is the most significant loss factor. Nevertheless, by compensating the mechanical loss for short time intervals using the generator force, the reciprocating motion can be kept alive for a rapid start without major energy
Abstract: Voltage sags are huge power quality problems for many industries. Voltage sags may cause tripping, production disturbances and equipment damages. Undervoltage tripping is one way of protecting equipment from getting damaged due to overcurrent during voltage sags. However, the undervoltage protection is usually set to break at an absolute voltage magnitude instead of at a relative voltage magnitude change. This may lead to both unnecessary tripping and non-tripping when necessary.
Abstract: Voltage sags and voltage interruptions are huge power quality problems for many industries. Voltage sags cause apart from eventual tripping, flux saturation, which cause large currents. This paper illustrates how the stator flux in a synchronous machine changes during voltage sags. It is shown that for some voltage sags, there will be flux saturation. Flux saturation causes both large currents and torque; these may fasten the aging of the machine. A comparison is done with a model without saturation included. This study includes only three-phase symmetrical voltage sags.
Abstract: Voltage sags and voltage interruptions are huge power quality problems for many industries. Voltage sags cause tripping of asynchronous machines by undervoltage or overcurrent protection and in some cases saturation of the flux. This paper gives a basic understanding of how voltage sags change the stator flux in line-operated asynchronous machines and under which circumstances saturation will occur. Most voltage sags will cause saturation. Flux saturation results in both large currents and torque; these may fasten the aging of the machine.
Abstract: Voltage sags and voltage interruptions are serious power quality problems for many industries. Apart from eventual tripping, voltage sags cause high torque peaks, which may cause damage to the shaft or equipment connected to the shaft. This paper shows how the torque depends on both the duration and the magnitude of voltage sags. First, a simple theory is presented, and then to verify the theory, simulations of a blast furnace blower located at the steel plant SSAB Oxelösund Sweden are performed. A line operated salient-pole synchronous machine powers the blower, which feeds the blast furnace with air. The conclusion is that voltage sags with durations equal to multiples of a whole cycle generate minimum torque peaks, and the maximum torque peaks are generated by voltage sags with durations equal to multiples of a whole cycle plus half a cycle.
Abstract: AbstractVoltage transients play an important part in the area of power quality. Transient overvoltages cause machine tripping due to breaking by overvoltage protection, which may lead to production losses. Apart from that, large torque peaks that may cause damage to the shaft or equipment connected to the shaft. High current peaks occur as well, which leads to thermal heating and tension. This paper shows on what conditions transients cause high peak torques and currents for synchronous machines, which is explained by a simple theory. Simulations verify the theory, and illustrate the torque and current peaks dependence on transient duration and magnitude.
Abstract: Voltage sags are a huge power quality problem for many industries. Voltage sags cause torque transients, which may cause damage to the shaft. This paper shows when there are torque and current peaks for voltage sags of types A - G for synchronous machines. An expression of the stator flux during and after voltage sags is derived, which explains why there are high torque peaks. Simulations verify this and illustrate the torque and current peaks dependence of voltage sag duration and magnitude. A general conclusion is that the peak torque depends on the sag magnitude and sinusoidal on the duration.
Abstract: Voltage sags and interruptions are a major power quality problem for many industries. When the power quality degrades too much, the protection equipment automatically turns off electric units. In many cases short voltage sags or interruptions that lasts for only a hundred milliseconds lead to stoppage for hours in the production, due to long start-up times for the industrial process. This results in production losses, which is very expensive. Simulations and models have been developed on a blast furnace process in the steel plant SSAB Oxelösund, located in Sweden. A line operated synchronous machine powers the blower, which feeds the blast furnace with air. The results show how sensitive the process is to voltage problems and by adjusting the settings in the protection equipment the number of unplanned stoppages may reduce.
Abstract: Voltage sags and interruptions are a big power quality problem for the industry. Protection equipment automatically breaks the circuit when the power quality is degraded too much. In many cases short voltage sags or interruptions that lasts for only a hundred milliseconds leads to stoppage for hours in the production. This is mainly due to long start-up times of the industrial process. Simulations have been done on a blast furnace blower in the steel plant SSAB Oxelösund in Sweden. A line operated synchronous machine powers this. If the remaining voltage is higher than 55% there is no need to break at all. These results show that changing the settings in the protection equipment may reduce the number of unwanted shutdowns. In addition, much attention has been paid to the torque variations during and after the sag, and how it depends on the duration of the voltage sag.
Abstract: Voltage sags can be a huge problem for many industries. Voltage sags lasting for hundred milliseconds can shutdown an industry for several hours, due to long start-up times. This will imply large costs for the company due to the subsequent loss in the production. Metal processes, especially the cold rolling mill, have been studied at company Outokumpu Copper in Sweden. Calculations of time constants have been done for the process and these are compared to the duration times of common voltage sags. In the worst case, a 10% voltage sag will shut down the cold rolling mill. The cold rolling mill will then be standstill in about half a second. Suggestions of methods to reduce the problem of the process in connection with voltage sags are presented.
Abstract: Voltage sags can be a huge problem for many industries. Voltage sags lasting for hundred milliseconds can shutdown an industry for several hours, due to long start-up times. This will imply large costs for the company due to the subsequent loss in the production. Metal processes, especially the hot rolling mill, have been studied at the steel mill SSAB Oxelösund in Sweden. Calculations of time constants have been done for the process and these are compared to the duration times of measured voltage sags at the same industry. In the worst case, voltage sag duration time of 10 ms may shutdown the rolling mill process. Suggestions of methods to reduce the problem of the process in connection with voltage sags are presented.
Abstract: Voltage sags and interruptions are a big power quality problem for the industry. Protection equipment automatically breaks the circuit when the power quality is degraded too much. In many cases short voltage sags or interruptions that lasts for only a hundred milliseconds leads to stoppage for hours in the production. This is mainly due to long start-up times of the industrial process. Simulations have been done on a blast furnace blower in the steel plant SSAB Oxelösund in Sweden. A line operated synchronous machine powers this. The results show that it is possible to reconnect to the mains if the voltage interruption is no longer than 150 ms long. If the remaining voltage is higher than 55% there is no need to break at all. These results show that changing the settings in the protection equipment may reduce the number of unwanted shutdowns.
Abstract: During the last decade, power quality has been recognised as a global problem. Among different types of power quality problems, voltage sags have been identified to be one of the most severe problems for different process industries. The most common reason to voltage sags is lightning strikes in power lines. Protection equipment, usually located at switchyards, disconnect faulted power lines as soon as possible, which is approximately 100 ms. Thus, the duration of voltage sags are approximately 100 ms. The sensitivity to voltage sags of electrical equipment in process industries can be observed as for instance malfunction, automatic turnoff or damages. This thesis gives an overview of three metals processes with focus on the sensitivity to voltage sags and interruptions. The inherent energy in the process is used to find the sensitivity. This energy may also be used to obtain "ride-through" for the processes. The three metals processes are a blast furnace process, a hot rolling mill process and a cold rolling mill process. The main attention in this thesis is paid to the blast furnace process, which is powered by a line-operated synchronous machine. The thesis shows that the protection equipment for electrical machines can be adjusted to avoid unnecessary shutdowns. It is also explained why there are high torque and currents during voltage sags as well as after voltage sags. It is shown that the first peak torque and current during the voltage sags is almost proportional to the voltage change, that is the voltage magnitude before the voltage sag minus the voltage magnitude during the voltage sag. The first peak torque and current after the voltage sag depends sinusoidal-like on the duration of the voltage sag and almost proportional to the voltage change during the voltage sag. There is no flux saturation during voltage sags, however after voltage sags saturation is very likely to occur. The thesis explains why and also how the flux is changed during and after voltage sags. The duration of voltage sags is in many cases set by the protection equipment located in switchyards. It is shown that the durations of voltage sags can be changed to durations that will cause less peak torque and current after voltage sags for line-operated AC-machines. It is also shown how this is theoretically achieved.
Abstract: Vindkraften är en av de snabbast växande förnybara energikällor i elsystemet, vilket är helt i linje med både Sveriges och EU:s mål. För elmarknaden finns det framförallt två utmaningar vid en större andel vindkraft i elsystemet - produktionens variation och förutsägbarhet. Produktionsvariationen är inte behandlad i denna utredning, men både variationen och förutsägbarheten är kopplade till behovet av reglerkraft, det vill säga att reglera produktionen till den nivå som konsumenterna använder. Förutsägbarheten är viktig eftersom försäljningen sker klockan 12.00 för nästkommande dygn på elmarknaden, det vill säga 12 - 36 timmar före produktionstimmen. En prognos behöver alltså göras för försäljningsvolymen, vilket är mycket svårt så långt i förväg för en intermittent källa som vindkraft. Det prognosfel som då uppstår måste om det är stort nog regleras med sekundärreglering som Svenska Kraftnät avropar och köper. Kostnaden för regleringen får de balansansvariga som orsakade prognosfelet betala. Mindre prognosfel på systemnivå regleras däremot enbart med hjälp av primärreglering och då debiteras ingen för det, men kostnaden som SvK har för att hantera detta får alla balansansvariga dela på genom avgifterna till SvK.
För att studera kostnaden för framtida prognosfel har ett antal scenarier med 10 - 55 TWh ny vindkraft i det svenska systemet utvecklats och undersökts.
I rapporten redovisas prognoser för balansfelens volymer samt kostanden för dessa balansfel för åtta olika tänkta aktörer som balansansvariga.
Abstract: The state of existing reliability and failure data in the public sources has been
investigated. The prime goal has been to evaluate the dataâs usefulness for
developing damage preventing measures. Some publicly available databases
exist, and the data has been presented in several papers in the literature. The
results from the investigation can seem quite negative. Detailed data are
lacking and the level of detailed reporting has even been decreasing in recent
years. Information on the impact of load condition on failures, which is an
important question, are lacking throughout in the statistics.
Some components dominate the failure statistics. These are for example the
gearboxes, where failures lead to long down times. Failures of the electrical
system lead to considerably shorter down times but the failure rate is much
higher. Severe rotor failures seem to be rare, but they occur and the
consequences can be dramatic.
Operators and insurance companies are demanding improved insight in
damage collection, maintenance and overall damage preventing measures.
Closer cooperation with these parties could be a fruitful way of gathering
more useful data.
Improvements for future databases are suggested. A structure for damage
collection is proposed.
Comparing experience of damage preventing measures from other industries,
knowledge about the nature of the damage mechanism and current practice in
the wind industry will be an important tool in the evaluation of different
damage preventing measures. This will be done in the following phases of this
project.
Abstract: Distributionstransformatorerna är i regel överdimensionerade och gjorda av konventionella material. Genom att byta ut gamla transformatorer mot nya transformatorer med nya material så kan stora förlustbesparingar ske, cirka 0,7 TWh/år, dvs cirka 300 Mkr/år. Som också beskrivits så inverkar övertoner på förlusterna, men hur hög övertonshalten är bör utredas vidare.
Abstract: Projektets mål var att studera och analysera konsekvenser för elnätet m.a.p. elektronisk last. Ska man bygga nya elnät på något annorlunda sätt, om man har 100 % elektronisk last jämfört med nuvarande byggsätt?
Förstudien tyder på att det rent tekniskt verkar som att nuvarande elnät klarar elektronisk last i de flesta fall utan större problem.
Detta gäller under förutsättning att den generösa dimensioneringen som nu tillämpas bibehålls. En högre andel elektronisk last innebär en reducering av lågspänningsnätens kapacitet. Dock är det oklart hur stor reduceringen är. Vi utnyttjar nu den höga kapacitet vi har i dagens nät, men om en snävare dimensionering skulle tillämpas kan problem uppstå.
Abstract: Sverige har ett ambitiöst mÃ¥l som syftar till att öka andelen förnybar energiproduktion. Energimyndighetens befintliga planeringsmÃ¥l är att Sverige skall producera 10 TWh Ã¥rligen frÃ¥n vindkraft Ã¥r 2015. Nyligen har Energimyndigheten föreslagit ytterligare ett planeringsmÃ¥l om en produktion av 30 TWh Ã¥r 2020. SvÃ¥righeten med vindkraft ligger i dess oregelbundna produktion och att produktion är svÃ¥r att förutsäga. Energin som vindkraften producerar säljs precis som alla annan producerad elektrisk energi pÃ¥ den nordiska elmarknaden â Nord Pool. För att göra det sÃ¥ mÃ¥ste produktionen prognostiseras pÃ¥ grund av att energin säljs dygnvis kl 12.00, det vill säga 12 â 36 timmar innan aktuell produktionstimme. Vindkraftproducenterna gör prognoser av sin elproduktion med hjälp av väderprognoser av vindhastigheter. Om tillverkarens produktion skiljer sig frÃ¥n sin planerade produktion som sÃ¥lts pÃ¥ elmarknaden, sÃ¥ kommer producenten att fÃ¥ betala för avvikelsen. Eftersom elkraftsystemet mÃ¥ste vara i balans, mÃ¥ste den som ansvarar för balansen i elkraftsystemet be nÃ¥gon annan elkraftproducent kompensera för obalansen när det finns en obalans (under- eller överproduktion). Detta kallas för reglering och kostar pengar för den kompenserande aktören. De aktörer som orsakar obalans fÃ¥r betala för sina obalanser. Kostnaderna är i enlighet med det reglerpris som rÃ¥der och fördelas mellan aktörer som orsakade obalanser. Processen kallas balansavräkning och äger rum dagen efter produktionsdagen.
Om en aktör vet att planen inte kommer att följas, till exempel om aktören har en uppdaterad vindprognos som visar en annan produktionsnivå, finns det en alternativ väg att gå. Den vägen är att köpa eller sälja obalansen vid intradagmarknaden Elbas, vilket kan göras så nära som en timme innan produktionstimmen. Nackdelen med handeln vid intradagmarknaden Elbas är att handeln i sig kostar pengar och att den nya prognosen fortfarande inte är exakt, det vill säga det nya prognosfelet kommer att kosta pengar på reglermarknaden.
I denna rapport har åtta olika aktörer skapats, som alla har balansansvar för sin produktion, vilket innebär att om de orsakar en obalans, så måste de betala upp- eller nedregleringspriser. Dessa aktörer är olika i den bemärkelsen att vissa är små och några är stora, vissa har koncentrerade vindkraftverk och några har vindkraftverk som är geografiskt utspridda. Dessa aktörers vindkraft har en samlad märkeffekt på 4 000 MW, och summan av deras årliga produktion uppgår till nästan 12 TWh. Den geografiska spridningen har valts så att 50% av energiproduktionen är förlagd till norr och 50% till söder. En aktör som kallas "en aktör" har också skapats, som består av samtliga åtta aktörer tillsammans. Denna aktör, har två syften: a) dels att tala om hur mycket obalans vindkraften tillsammans orsakar samt dess kostnader, och b) dels om alla vindkraftsaktörer skulle förena sig, vad har de då för möjligheter till minskade kostnader.
De obalanser som dessa aktörer skapar i systemet har modellerats med hjälp av studier av prognosfel från vindkraftsverken vid Horns Rev och andra publicerade resultat av prognosfel. Det är välkänt att det prognostiserade felet minskas om lokaliseringen av vindkraften sprids ut, vilket har beaktats i modellen. Modellen ger svar på den obalans som aktörerna skapar samt elkraftsystemets totala obalans. För att beräkna kostnaden för det prognostiserade felet, har en utvecklad prismodell av Klaus Skytte vid Risö-laboratoriet i Danmark använts. Denna modell innehåller parametrar som har uppskattats för marknadsläget under 2006. Genom att skapa prognosfel för alla aktörer genom slumptalsgenerering som är normalfördelade i Excel för ett helt år, har det varit möjligt att beräkna aktörernas kostnader för deras prognosfel.
Det finns en möjlighet att uppdatera prognosen och placera (sälja eller köpa) det prognostiserade felet på intradagmarknaden Elbas, detta fall har också utvärderats. Men att uppdatera en prognos kommer också att generera ett nytt prognosfel, som naturligtvis i allmänhet är mindre än det ursprungliga prognosfelet. Detta har också tagits med vid kostnadsberäkningen av att agera på intradagmarknaden Elbas.
Abstract: Denna rapport är ett komplement till projektet 100% elektronisk last inom Elforsk och utgör en omvärldsanalys av omrÃ¥det dÃ¥ det nämnda projektet var fokuserat pÃ¥ Sverige. Det finns en del forskning i världen om elektroniska laster även om det väldigt sällan gÃ¥r under beteckningen elektronisk last, utan oftast om specifika produkter som t ex datorer, lÃ¥genergilampor, etcetera. Ãverlag kan konstateras att de flesta elektroniska laster har övertoner och framförallt är det den tredje övertonen (150 Hz) som är den dominerande övertonen. Det finns dessutom en del studier om hur övertonerna drabbar distributionsnätet i from av uppvärmda transformatorer och dess relaterade kostnader. Andra abonnenter drabbas naturligtvis ocksÃ¥ av dessa övertoner vilket kan leda till ökade förluster i apparaterna hos abonnenterna. Men, överlag finns väldigt fÃ¥ artiklar om kostnaden för elkvalitetsrelaterade problem. En bilaga som skrivits av Andrea Badano, Elforsk, med titeln âElnätsproblem vid storskalig användning av olinjär last - internationell utblickâ har bifogats dokumentet dÃ¥ den ger en bra komplettering till omvärldsanalysen.
Abstract: Voltage sags and voltage interruptions are a major power quality problem for many industries. When the power quality is degraded to a certain level, protection equipment automatically turns off electric units. In many cases short voltage sags or voltage interruptions that last for only a hundred milliseconds lead to production stoppage for hours in industries, due to the long start-up times for industrial processes. This results in production losses, which may be very expensive. The definition of a voltage sag according to standards is a momentary decrease (10% - 90%) in the root mean square (RMS) voltage magnitude for a duration time of 20 ms to 1 min. The most common reason for these phenomena is lightning strikes on power lines. Voltage sag is the effect of such a strike and when protection equipment detects the sag, it breaks the electric circuit causing a voltage interruption. The most common voltage sag duration is about 100 ms. Three metal processes have been studied to find their sensitivity to voltage sags and the ability to ride-through voltage sags. These three processes are a) a hot rolling mill powered by two 11.2 MW synchronous machines, b) a cold rolling mill powered by 400 kW DC-machines and c) a blast furnace process powered by a 3.6 MW blast furnace blower. The three processes have been modelled and calculations and simulations have been carried out. Parameters for the processes have been found from measurements on the processes and from data sheets provided by ABB and the respective company mentioned in a), b) and c). The results show that the hot rolling mill is the most sensitive process; voltage interruptions that are as short as 10 ms will stop the process in the worst case. However the process is in most cases not that sensitive, in general the process will stop when the voltage interruption is longer than 100 ms. The cold rolling mill will in the worst case stop for voltage interruptions longer than 400 ms and in the best case stop for interruptions longer than 3.5 s. However, since the process is powered by DC-machines, short and deep voltage sags may result in high currents, which lead to automatic shutdown by the overcurrent protection. The results from the blast furnace process show that the blowing synchronous machine can handle voltage sags that are smaller than 45%. It is also showed that the settings in the undervoltage protection may be adjusted, which reduce the sensitiveness of the process. The air-pressure in the pipeline is negligibly affected during the time of the voltage sags that the machine can handle.
