Utfört examensarbete undersöker vinkelfelet i mätkretsen för riktade jordfelsskydd och hur det påverkar dess felbortkoppling. Uppkomna vinkelfel i mätkretsen kan påverka det riktade jordfelsskyddet så att verklig felström och uppmätt felström inte stämmer överens, vilket kan leda till uteblivna eller obefogade felbortkopplingar. Vattenfall ställer krav på att vinkelfelet får uppgå till max ±2 grader för mätkretsen. Eftersom vinkelfelet i många fall har en hög påverkan på jordfelsskyddets noggrannhet undersöks vad Vattenfalls vinkelkrav egentligen innebär. Största orsaken till vinkelfelet uppstår oftast i strömtransformatorn och därför undersöks hur mycket två strömtransformatorer med olika klassificeringar som är vanliga i elnätet påverkar vinkelfelet i mätkretsen. Jordfel är det vanligast uppkomna felet i mellanspänningsnät och dess storlek beror till stor del på hur mycket kapacitivt bidrag som finns på linjerna samt värdet på nollpunktsresistorn. Det kapacitiva bidraget från linjen kompenseras centralt i fördelningsstationen och ibland lokalt ute på ledningen. Den högst tillåtna centralt kompenserade delen av en linje får vara 30 A, vid reservdrift av en linje kan denna del uppgå till 60 A. Vinkelfelet har en högre påverkan vid stora kapacitiva bidrag och vid låga värden på nollpunktsresistorn. I många fall sitter det flera riktade jordfelsskydd på samma linje där selektivitet alltid eftersträvas. Vinkelfelet kan ha en negativ påverkan på denna selektivitet. Genom beräkningar, simuleringar och provningar har ett antal slutsatser dragits. Vattenfalls vinkelkrav ger en otydlig bild angående tillåten påverkan på jordfelsskyddet. Med rätt val av strömtransformator påvisas att det troligtvis är möjligt att skärpa vinkelkravet. För att minska vinkelfelets påverkan kan den högst tillåtna centralt kompenserade delen minskas och/eller öka värdet på nollpunktsresistorn. En beloppsselektivitet på 1000 Ω kan inte alltid tillämpas då vissa fall kräver en beloppsselektivitet på 2000 Ω. Genom att sätta nollpunktsspänningen som utlösningsvillkor och nollpunktsströmmen som frigivningsvillkor kan enligt studien troligen ett noggrannare jordfelsskydd uppnås. / This bachelor's thesis examines the angular error in the measurement circuit for directional earth-fault protection and how this error affects the fault disconnection. Angular errors in the measurement circuit can affect the directional earth-fault protection in such a way that the real fault current and the measured fault current do not match. This can lead to missed or unwarranted fault disconnections. Vattenfall has a requirement which states that the angular error must not exceed ±2 degrees for the measurement circuit. Since the angular error in many cases has a high impact on the earth-fault accuracy, an investigation concerning what Vattenfalls angle requirement really means. The main cause of the angular error usually occurs in the current transformers and therefore two commonly used current transformers in the grid with different classifications and their impact on the angular error in the measurement circuit are examined. Ground fault is the most common fault which occurs in a distribution network, its size depends largely on the amount of capacitive current which the grid contributes with as well as the size of the neutral grounding resistor. The capacitive contribution of the grid compensates centrally in the distribution station and sometimes locally on the line. The maximum permitted centrally compensated part of a line is limited to 30 A, this central part can go up to 60 A in case the line needs to be fed from a second distribution station. The angular error has a higher impact if the capacitive contribution is high and for low values of the neutral grounding resistor. In many cases more than one earth-fault protection are found on the same line, in these cases selectivity is always pursued. The angular error may have a negative effect on the selectivity. By calculations, simulations and tests a number of conclusions can be drawn. Vattenfalls angle requirement gives an unclear picture concerning the permitted impact on the earthfault protection. Moreover selecting the correct current transformer demonstrates that the angular requirement can probably be sharpened. To reduce the influence of the angular error the maximum permitted centrally compensated part be reduced and/or the value of the neutral grounding resistor can be increased. A selectivity of 1000 Ω can not always be applied since certain cases require a selectivity of 2000 Ω. By setting the zero sequence voltage as the trigger condition and the zero sequence current as the realese condition, according to this study it may be possible to achieve a more accurate earth-fault protection.

The electric vertical take-off and landing (EVTOL) platform is opening a new market segment that is disrupting the commercial and military aircraft industry. This particular vehicle platform is filling the gap between road vehicles and aircrafts. The main idea is to avoid the gridlock in major metropolitan cities where a journey that should take 30 minutes now takes more than one hour. Key enablers such as the newly developed infrastructures known as Vertiports and the move of electrification of aircrafts have driven this new market segment with fast time to market. To enable the deployment of these EVTOLs in the commercial world, their fault behavior needs to be known as faults will happen, a fault mitigation strategy must be developed to ensure that when the fault happens, the EVTOL and its passengers along with its surrounding are protected from catastrophic failures. To give a brief context on what these EVTOL platforms are, potential and developed EVTOLs in the market currently are introduced. The categorization of these platforms is done within four types of categories being Helicopters, Multi-Rotor, Lift & Thrust and Tilt-X. Their general advantages and disadvantages are discussed and the categories are rated in terms of which platform could be the most viable option to be in service by 2024. Their main electrical distribution system is introduced with their critical components and how they can fail. Each critical component such as the battery, electrical propulsion unit (EPU), protection devices, power distribution units and auxiliary electrical loads are discussed in details. The thesis discusses one of the main safety aspects of an EVTOL, which is protection of a propulsion unit. The critical electrical faults in the EPU are introduced along with their behavior on the EVTOL electrical distribution system (EDS). Open circuit faults and short circuit faults from the inverter and its power devices to the electric motor are analyzed. Furthermore, the sensor failures such as the rotor position sensor and the current and voltage sensors are discussed. The controller stage failures are discussed as well as it becomes a critical component that can fail in many ways. Once the electrical faults are discussed, a fault mitigation strategy (FMS) is introduced for each fault ranging from a simple inverter disabling strategy, to a sensorless control law for the loss of position sensor. A protection device known as the solid state power controller (SSPC) is inserted at the input of the EPU and its design is discussed for a 270VDC/180A modular architecture. This SSPC becomes the redundant and final protection stage of the EPU to ensure if the developed FMS fail to protect the EPU, the SSPC can isolate the EPU from the rest of the EVTOL EDS. The main contribution of the thesis is the systematic approach to fault analysis and mitigation/protection strategies that were not addressed in literature so far for this type of platform. The use of a single FMS for multiple faults is introduced where the aim is to reduce the efforts for verification and validation (V&V) of the corresponding software and firmware. Finally, the practical implementation challenges of the SSPC are discussed and shown in experimental lab setups. / Dissertation / Doctor of Philosophy (PhD)

The modular multi-level converter (MMC) is the most prominent interface converter used between the HVDC grid and the HVAC grid. One of the important design challenges in MMC is to reduce the capacitor size. In the current practice, a rather large capacitor bank is required to store line-frequency related circulating energy, even though a number of control strategies have been introduced to reduce the capacitor voltage ripples. In the present paper, a novel control strategy is proposed by means of harmonic injections in conjunction with gain control to completely eliminate both the line frequency and the second-order harmonic of the capacitor voltage ripple. Ideally, the proposed method works with the full bridge topology. However, the concept also works with half bridge topology with a significant reduction of line frequency related ripple. To gain a better understanding of the nature of circulating energy and the means of reducing it, the method of state plane analysis is employed to offer visual support. In addition, the design trade-off between full bridge MMC and half bridge MMC is presented and a novel control strategy for a hybrid MMC is proposed. Finally, the work is supported with a scaled down hardware demonstration. / Master of Science

In any power system, fault means abnormal flow of current. Insulation breakdown is the cause of fault generation. Different factors can cause the breakdown: Wires drifting together in the wind, Lightning ionizing air, wires with contacts of animals and plants, Salt spray or pollution on insulators. The common type of faults on a three phase system are single line-to-ground (SLG), Line-to-line faults (LL), double line-to-ground (DLG) faults, and balanced three phase faults. And these faults can be symmetrical (balanced) or Unsymmetrical (imbalanced).In this Study, a technique to predict the zero crossing point has been discussed and simulated. Zero crossing point prediction for reliable transmission and distribution plays a significant role. Electrical power control switching works in zero crossing point when a fault occurs. The precision of measuring zero crossing point for syncing power system control and instrumentation requires a thoughtful approach to minimize noise and external signals from the corrupted waveforms A faulted current waveform with estimated faulted phase/s, the technique is capable of identifying the time of zero crossing point. Proper Simulation has been organized on MATLAB R2012a.

Master's thesis deals with use of electronic instrument transformers (sensors) in the protection system in medium-voltage substation. Substation consists of 2 incoming feeders, 2 outgoing feeders for motors, 2 outgoing feeders for power transformers, measuring, bus coupler and bus riser feeder. Incoming feeders are connected to distribution system E.ON by cable lines which were proposed. Protected machines (power transformers and motors with rated power) are connected to switchgear panels of UniGear ZS1 type by cable lines too. Proposed protection system is based on the short-circuit conditions, standard CSN 33 3051 recommendations as well as theoretical backgrounds acquired from technical papers and other publicated literature according to the bibliography. For selected protection functions are defined their parameters. Control, monitoring and protection functions provides REF 542plus relay. Consequently, secondary tests which are part of the commissioning, are given in the practical part of thesis. Secondary tests were performed by relay test system FREJA 300 by Megger. Results of tests are displayed in tripping characteristics.

En tranmissionsledning är delen av elsystemet som överför ström från kraftverk till slutanvändare. Därför är det av vikt att en transmissionslinje alltid ska vara skyddad. Syftet med detta examensarbete var att utveckla och prova en konfiguration av teleskyddsschema med kommunikation mellan två reläskydd med distans- och jordfelsskydd över längsdifferentialskyddets kommunikationskanaler. Detta för att skydda elnätet och koordinera utlösningstiden.  Konfigurationen av reläskydden har utvecklats med mjukvaran ABB PCM600, och funktionerna som valdes är adekvata funktioner för distansskydd, jordfelsskydd och teleskyddsschema.  Provningen delades till två delar. Först verifierades funktionaliteten av distansskyddet och jordfelsskyddet på var och en av reläskydden som självständig skydd, detta för att säkerställa självständiga funktionaliteten av var och en av reläskydden med distans- och jordfelsskydd i fall teleskyddschemat inte var fungerande. Därefter har teleskyddsschemats sändnings- och mottagningsfunktionalitet mellan reläskydden för både distansskyddet och jordfelsskyddet kontrollerats att möjligtvis fungera genom att endast använda en fiberoptisk kabel. Ett fungerande och pålitligt teleskyddsschema med kommunikation mellan två reläskydd kunde säkerställas fungerande genom användning av längsdifferentialskyddets kommunikationskanaler för distans- och jordfelsskydd. Teleskyddsschemat förstärkte distansskyddet och jordfelsskyddet genom accelerering av utlösningssignal, och som en konsekvens samordna utlösningstiden mellan reläskydden vid felavkänning, vilket förbättrade skyddet ännu mer. Direkt kommunikation mellan reläskydden har visat sig vara användbar och tillämpbar, och en användning av sådan implementation är möjlig för isolerade linjer och anläggningar samt mikronät som inte kräver en kontinuerlig övervakning och kontroll. / A transmission line is the part of the electrical system that transfers current from power stations to the end-user. Therefore, it is of importance that a transmission line stays always protected. The purpose of this bachelor thesis is to develop and test a configuration for teleprotection scheme communication between two protective relays with distance and earth fault protection using line differential protection communication channels, that is to protect the electrical grid and coordinate tripping time. The configuration has been developed with the software ABB PCM600, and the chosen functions are adequate functions for distance and earth fault protection and the Teleprotection scheme. The testing has been divided into two parts. Primarily, the functionality of distance and earth fault protection has been tested and verified on each one of the protective relays, that is to ensure the independent functionality of each one of the protective relays with distance and earth fault protection in case there is no Teleprotection scheme functioning. next, the sending and receiving functionality of the teleprotection scheme between the protective relays with distance protection and earth fault protection has been controlled to be possibly functioning through using only a fiber-optic cable. A functioning and reliable Teleprotection scheme with communication between two protective relays could be verified functioning through using line differential protection communication channels for distance and earth fault protection. The Teleprotection scheme strengthened the distance protection and earth fault protection through acceleration of trip signal, and as a consequent coordinating the trip time in case of fault detection. Direct communication between protective relay using fiber-optic cable has proven to be useful and applicable, and a using of such implementation is possible for isolated electrical line and facilities and also micro grids that does not require continuous monitoring and control.

Master thesis Testing of Directional Earth Fault Protections Using the Experimentally Obtained Fault Records deals with the protective functions of earth fault protections during earth faults in compensated medium voltage distribution network and their testing options. At the beginning of the thesis we charakterize operation of medium voltage distribution system in general. We begin with definition and characteristics of earth fault and its compartmentalization by the type of the fault, size of the transition resistance and duration. We also mention grounding methods of node winding transformer on medium voltage distribution network and we describe the most common of them in detail, i.e. network grouded through the arc suppression coil and its operation with automatic switching auxiliary resistor. In this part of the thesis we discuss the localization of the earth fault using passive static methods in compensated systems, which include wattmetric, admittance and conductance method. In next section we deal with the fault records stored in COMTRADE file format, its structure and all elements of its configuration and data file. We create and describe an example of converting ADF file format, recorded by Yokogawa oscilloscope fault recorder, into COMTRADE file format using Microsoft Excel program and M-File created in the MATLAB program. In the practical part we introduce workspace devices and software, which includes secondary testing equipment OMICRON CMC 256plus and its software OMICRON Test Universe with Advance Transplay test module, we further describe multifunctional earth fault protection RYo from PROTECTION & CONSULTING, s. r. o. and machine terminal REM 543 from ABB and their protective functions. The last part describes the actual testing of parallel connected earth fault protection with COMTRADE fault records by Advance Transplay test module in the OMICRON Test Universe. In the conclusion we describe evaluation of the suitability of each protective functions of earth fault protection in a variety of sizes the transition resistance at the earth fault location.

The thesis deals with the proposal, implementation and evaluation of test for fault condition indicators. Thesis focusing on earth fault indicators based on admittance principles. These indicators must be able to evaluate earth faults in compensated, compensated with auxiliary resistor, unearthed and high-resistance earthed networks. The proposed tests verify the current and voltage measurement errors in inputs including monitored characteristic variables such as conductance and susceptance. The proposed test are applied to a selected ample of the fault indicator. As part of the tests, the indicator is subjected to secondary test using the Omicron CMC256plus tester as well as test on fault records that have been converted to COMTRADE for this purpose. The last series of tests carried out uses the physical model of the medium voltage system, where the tested equipment is subjected to fault states in the compensated whit auxiliary resistor system and isolated system. Furthermore, part of the thesis is research of new methods of earth fault detection, including their principles and function description. Also included in the thesis is an overview of manufacturers of indicators, or protection, who are involved in the production of earth fault protection.

The main goal of this thesis is to develop practical digital controller architectures for multi-phase dc-dc converters utilized in low power (up to few hundred watts) and cost-sensitive applications. The proposed controllers are suitable for on-chip integration while being capable of providing advanced features, such as dynamic efficiency optimization, inductor current estimation, converter component identification, as well as combined dynamic current sharing and fast transient response. The first part of this thesis addresses challenges related to the practical implementation of digital controllers for low-power multi-phase dc-dc converters. As a possible solution, a multi-use high-frequency digital PWM controller IC that can regulate up to four switching converters (either interleaved or standalone) is presented. Due to its configurability, low current consumption (90.25 μA/MHz per phase), fault-tolerant work, and ability to operate at high switching frequencies (programmable, up to 10 MHz), the IC is suitable to control various dc-dc converters. The applications range from dc-dc converters used in miniature battery-powered electronic devices consuming a fraction of watt to multi-phase dedicated supplies for communication systems, consuming hundreds of watts. A controller for multi-phase converters with unequal current sharing is introduced and an efficiency optimization method based on logarithmic current sharing is proposed in the second part. By forcing converters to operate at their peak efficiencies and dynamically adjusting the number of active converter phases based on the output load current, a significant improvement in efficiency over the full range of operation is obtained (up to 25%). The stability and inductor current transition problems related to this mode of operation are also resolved. At last, two reconfigurable digital controller architectures with multi-parameter estimation are introduced. Both controllers eliminate the need for external analog current/temperature sensing circuits by accurately estimating phase inductor currents and identifying critical phase parameters such as equivalent resistances, inductances and output capacitance. A sensorless non-linear, average current-mode controller is introduced to provide fast transient response (under 5 μs), small voltage deviation and dynamic current sharing with multi-phase converters. To equalize the thermal stress of phase components, a conduction loss-based current sharing scheme is proposed and implemented.

The main goal of this thesis is to develop practical digital controller architectures for multi-phase dc-dc converters utilized in low power (up to few hundred watts) and cost-sensitive applications. The proposed controllers are suitable for on-chip integration while being capable of providing advanced features, such as dynamic efficiency optimization, inductor current estimation, converter component identification, as well as combined dynamic current sharing and fast transient response. The first part of this thesis addresses challenges related to the practical implementation of digital controllers for low-power multi-phase dc-dc converters. As a possible solution, a multi-use high-frequency digital PWM controller IC that can regulate up to four switching converters (either interleaved or standalone) is presented. Due to its configurability, low current consumption (90.25 μA/MHz per phase), fault-tolerant work, and ability to operate at high switching frequencies (programmable, up to 10 MHz), the IC is suitable to control various dc-dc converters. The applications range from dc-dc converters used in miniature battery-powered electronic devices consuming a fraction of watt to multi-phase dedicated supplies for communication systems, consuming hundreds of watts. A controller for multi-phase converters with unequal current sharing is introduced and an efficiency optimization method based on logarithmic current sharing is proposed in the second part. By forcing converters to operate at their peak efficiencies and dynamically adjusting the number of active converter phases based on the output load current, a significant improvement in efficiency over the full range of operation is obtained (up to 25%). The stability and inductor current transition problems related to this mode of operation are also resolved. At last, two reconfigurable digital controller architectures with multi-parameter estimation are introduced. Both controllers eliminate the need for external analog current/temperature sensing circuits by accurately estimating phase inductor currents and identifying critical phase parameters such as equivalent resistances, inductances and output capacitance. A sensorless non-linear, average current-mode controller is introduced to provide fast transient response (under 5 μs), small voltage deviation and dynamic current sharing with multi-phase converters. To equalize the thermal stress of phase components, a conduction loss-based current sharing scheme is proposed and implemented.