Series capacitors are used in electric transmission lines to increase their power transfer capacity. They compensate for the inductive reactance of the line. They offer a useful alternative to building new lines, in view of economic and environmental constraints. However, during transmission line faults, the presence of series capacitors causes problems for distance protection relays. Distance protection is the most widely used protection method in transmission lines, due to its relatively simple working principle and its ability to work with only local measurements of voltage and current. As the number of series compensated transmission lines is increasing, and the typical compensation level is also increasing, it has become essential to investigate protection methods that can be employed in place of traditional distance protection in series compensated lines.

This thesis addresses the problems associated with line protection in the presence of series capacitor compensation. The first part is an assessment of the performance of traditional distance relays in cases with high levels of series compensation. This was based both on simulation studies and on published works describing research studies and industry experience with series capacitor projects and the related line-protection issues. It is concluded that traditional distance protection cannot be used reliably with high levels of series compensation. The second part of the thesis describes some alternative protection methods that are developed and studied as candidates for better single-ended protection of series-compensated lines. These are based on incremental quantities, Lissajous curves and RL/RLC line models. These methods show positive results for single ended protection of series compensated lines.The incremental-quantity based method is fast and operates reliably, but faces under-reach problems with fault resistance. The Lissajous-curve basedmethod can be used as an alternative to the Fourier transform and has some advantages in overcoming inversion situations, but it requires at least a cycle of data to operate. The RL- and RLC-model based solutions can also operate fast, but lose accuracy with higher fault resistances. All the proposed protection methods are extensively tested, using data from fault test cases generated with PSCAD, and algorithms developed in Matlab.

Seriekondensatorer används i elektriska transmissionsledningar för att öka deras kraftöoverföringskapacitet. De kompenserar för ledningens induktiv reaktans. På grund av ekonomiska och miljömässiga begränsningar erbjuder de en användbar alternativ till att bygga nya ledningar. Vid fel i ledningenkan dock seriekondensatorer orsakar problem för distansskyddsreläer. Distansskydd är den mest använda skyddsmetoden hos transmissionsledningar, som konsekvens av sitt relativt enkelt arbetsprincip och av att endast lokala mätningar av spännings och ström behövs. Då det finns ökningar i antalet seriekompenserad transmissionsledningar samt deras kompensationsnivåer, har det blivit väsentligt att utreda skyddsmetoder som kan användas i stället för traditionellt distansskydd.

Denna avhandling tar upp problematiken av reläskydd hos seriekompenseradeledningar. Den första delen är en bedömning av prestationen av traditionella distansskyddsreläer vid fall med höga seriekompenseringsnivåer. Detta baserades både på simuleringsstudier och på publicerade arbeten som beskriverforskningsstudier och branscherfarenhet av skydd hos seriekompenseradeledningar. Man drar slutsatsen att traditionellt distansskydd inte kan användas på ett tillförlitligt sätt med höga seriekompenseringsnivåer. Den andra delen av avhandlingen beskriver några alternativa skyddsmetoder som utvecklas och studeras som kandidater för bättre skydd av seriekompenserade ledningar. Dessa är baserade på inkrementella storheter, Lissajous-kurvor och RL/RLC ledningsmodeller. Dessa metoder visar positiva resultat för kommunikationsoberoende skydd av seriekompenserade linjer. Metoden baserad på inkrementella storheter är snabb och fungerar tillförlitligt, men den har problem med underräckning vid högre felmotstånd. Den Lissajous-kurvabaseradmetoden kan användas som ett alternativ till fourier transform och har vissa fördelar för att övervinna inversionssituationer, men den kräver minst en periodav data. Den RL- och RLC-modellbaserade metoderna kan också fungera snabbt, men de förlorar noggrannhet med högre felmotstånd. Alla föreslagna skyddsmetoder är utförligt testad med data genererade från PSCAD simuleringar och algoritmer utvecklade i Matlab.

Series capacitors are installed in transmission lines to increase power transfer capacity. However, their addition creates challenges for the line protection. Security and speed of phasor based protection schemes that work with local measurements (communication independent) are severely affected in the presence of series capacitors. Therefore, time-domain based protection methods may be considered as a potential solution for communication independent protection of series compensated lines. In this paper, an incremental quantity based protection scheme is presented for series compensated lines with the capacitor in the middle of the line. The method involves estimating the voltage across the capacitor bank, based on the current in the capacitor bank and metal oxide varistor during faults. Then this capacitor voltage estimation is used to implement the incremental quantity protection. The incremental quantity method consists of fault detection, phase selection, directional discrimination and distance estimation. A PSCAD model of a 500 kV, 200 km transmission line is used to simulate fault cases for evaluating the method. The proposed method is tested with different compensation levels, fault types, fault positions, inception angles, fault resistances and source impedance ratios. The results show that the proposed method can meet the dependability and security demands for the protection of series compensated lines.

Series capacitors are installed in transmission lines to increase power transfer capacity. However, their addition creates challenges for the line protection. Security and speed of phasor based protection schemes that work with local measurements (communication independent) are severely affected in the presence of series capacitors. Therefore, time-domain based protection methods may be considered as a potential solution for communication independent protection of series compensated lines. In this paper, an incremental quantity based protection scheme is presented for series compensated lines with the capacitor in the middle of the line. The method involves estimating the voltage across the capacitor bank, based on the current in the capacitor bank and metal oxide varistor during faults. Then this capacitor voltage estimation is used to implement the incremental quantity protection. The incremental quantity method consists of fault detection, phase selection, directional discrimination and distance estimation. A PSCAD model of a 500 kV, 200 km transmission line is used to simulate fault cases for evaluating the method. The proposed method is tested with different compensation levels, fault types, fault positions, inception angles, fault resistances and source impedance ratios. The results show that the proposed method can meet the dependability and security demands for the protection of series compensated lines.

In Bangladesh, despite available feedstock for producing biogas, the development of biogas production has been very slow. The objective of this research was to study the drivers for and barriers to biogas technology implementation in the country. As the research involved different types of stakeholders related to biogas production, the outcome provides clarity about the factors influencing the profusion of biogas production in Bangladesh. The outcome of the study identifies poor research and development, lack of coordination among stakeholders, an immature biogas market, lack of awareness and no feed-in tariff policy as the main barriers. In the case of drivers, the motivation of producing biogas as an efficient way of using waste, the availability of local experts, the attractiveness of a growing renewable energy market and the contribution of biogas technology in adaptation to climate change were found to be the most important factors. The study’s outcomes are found to be similar to other studies from developing countries with similar socio-economic status. In accordance with the important drivers and barriers identified in this study, recommendations for increasing the diffusion of biogas in Bangladesh are also presented at the end of the article.

Series capacitors increase the power transfer limit of transmission lines. However, the protection of series compensated lines using only local measurement is challenging. Phasor based distance protection experiences delay and directional problems in the presence of a series capacitor. This paper presents an incremental quantity based distance protection algorithm for series compensated lines. The algorithm uses instantaneous voltage and current measurement from the local bus. It consists of capacitor voltage estimation, fault detection, phase selection, directional discrimination and distance estimation. The algorithm is extensively tested based on simulations with a line-end series capacitor, considering different source impedance ratios, fault inception angle, compensation levels, and fault resistance, location and type. This time-domain method is shown to work well, with fast decision time.

The introduction of series capacitors in transmission lines causes problems in terms of reliability and the security of distance protection relays. As distance protection is widely used in the transmission network, the challenge of applying it to series compensated lines has been taken up by utilities and relay manufacturers in various ways. In the field of power system protection, developments are largely driven by relay manufacturers, and are often not published in the academic literature; the status and trend of the relay manufacturer’s development are better found in their product manuals and patent activity. Further insight into specific implementations by transmission utilities can be found from publications in industry-led forums and some academic journals. This article surveys the status and development of distance protection for series compensated lines, with a focus on industrial implementation and practical considerations. Factors that influence the protection of series compensated lines are presented. Implementation examples reported by utilities are summarized as examples of the different situations encountered and the methods used to deal with them. It is observed that many utilities use communication-aided protection in series compensated lines, and distance protection is used with reduced reach. Solutions described in relay manuals are presented to demonstrate the manufacturers’ approaches to problems associated with series capacitor protection. While there are methods to counter voltage inversion, current inversion seems to represent a more serious challenge. A patent overview indicates the trends in this domain to be moving towards time-domain-based faster protection methods.

This data set contains time series data of different simulated fault cases in high voltage series compensated transmission lines. The simulation is done in PSCAD using the Python automation library. The capacitor is located at one of the line terminals with CT and VT. The modelled line is 500 kV and 200 km long. The simulation is run for 1 second with 10 kHz sampling rate. 

Each file contains 7 data in the following order, 

Time, Voltage phase A, Voltage phase B, Voltage phase C, Current phase A, Current phase B, Current phase C.

The variables used to study different test cases are shown below,

Fault inception angle (phase A): 0 and 90 degreeSource impedance ratio: 0.20 and 0.35Capacitor level: 94 µF(50%), 78 µF(60%), 67 µF(70%)Fault resistance: 0.10, 10, 20, 30 ohmFault location: 10 km reverse, 10 km, 50 km, 100 km, 125 km, 150 km, 155 km, 160 km. 165 km, 170 km, 180 km, 190 kmFault type: No-fault, AG, BG, CG, ABG, CAG, BCG, ABCG, AB, CA, BC, ABC

All these factors lead to 6912 test cases in total. The test cases are organized in four (4) zipped folders each containing 1728 test cases. The PSCAD model file and an example python script that can be used to automate the simulations are also included herewith for anyone interested to replicate the results. 

This data set contains time series data of different simulated fault cases in high voltage series compensated transmission lines. The simulation is done in PSCAD using the Python automation library. The capacitor is located in the middle of the line. The model of the line is given in the attached pdf file. The CT and VT are located at bus S. The distance are counted from bus S. The modelled line is 500 kV and 200 km long. The simulation is run for 1 second with 10 kHz sampling rate. 

Each file contains 10 data in the following order, 

Time, Voltage phase A, Voltage phase B, Voltage phase C, Current phase A, Current phase B, Current phase C, Voltage across capacitor phase A, Voltage across capacitor phase B, Voltage across capacitor phase C.

The variables used to study different test cases are shown below,

Fault inception angle (referred to phase A voltage): 0 and 90 degreeSource impedance ratio: 0.20 and 0.35Capacitor compensation level: 94 µF(50%), 78 µF(60%), 67 µF(70%)Fault resistance: 0.10, 10, 20 ohmFault location: 10 km, 30 km, 50, 70 km, 90 km, 95 km, 105 km, 110 km, 130 km, 150 km, 160 km, 170 km, 180 kmFault type: No-fault, AG, BG, CG, ABG, CAG, BCG, ABCG, AB, CA, BC, ABC

All these factors lead to 5616 test cases in total. The test cases are organized in four (4) zipped folders each containing 1404 test cases. The PSCAD model file and an example python script that can be used to automate the simulations are also included herewith for anyone interested to replicate the results. 

Introduction of series capacitors in transmission lines can cause problems with reliability and security of distance protection, due to problems such as current inversion, voltage inversion and sub-synchronous oscillation. Distance protection is widely used for transmission lines and has desirable features not available from traditional alternatives, which has motivated attempts to adapt it to work better with series capacitors. Research and development in overcoming the challenges using distance protection in series compensated lines have also been actively pursued during this period. Thus there is a need to summarize and systematically categorize developments, to show recent trends and highlight further research opportunities. This paper aims to fill that gap by a thorough literature survey of distance protection of series compensated lines, including a clear background of the problems that need to be solved. The scope of this work is limited to distance protection schemes that work with local measurements only. It is observed that the developments in this domain are largely concentrated on voltage drop estimation across capacitor bank, phasor estimation and adaptive protection schemes. This work will provide an overview of the latest developments for experienced researchers and will be a reference for new researchers interested in this domain.

Series compensation of transmission lines creates several challenges for distance protection, particularly at the high compensation levels that have recently become more common. In this paper, the effect of high levels of series compensation on distance protection is evaluated, using a PSCAD simulation model of a 500 kV, 200 km transmission line with a series capacitor bank. The capacitor bank model includes overvoltage protection using a metal oxide varistor (MOV) and bypass circuit breaker. Compensation levels of 70%, 100% and 140% are simulated and phase to ground faults are simulated at several positions along the line, with fault resistance of 0 Ω and 30 Ω and fault inception angle of 0 ° and 90 °. It is observed from the simulation results that traditional distance protection experiences severe challenges at high levels of series compensation. With increasing compensation level, an increased length of line experiences voltage inversion and current inversion during a fault. The fault trajectories in the R-X plane show that voltage and current inversion during a fault can cause directional problems and delay for the distance relay. Sub-synchronous oscillation (SSO) is observed for faults in series compensated lines, causing over-reach and under-reach problems as well as delayed relay operation.