E. Kontos

Bio: E. Kontos is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Fault (power engineering) & Grid. The author has an hindex of 14, co-authored 31 publications receiving 780 citations.

Trends of offshore wind projects

Abstract: The aim of this paper is to present the current status of the offshore wind industry and to identify trends in Offshore Wind Projects (OWPs) This was accomplished via a thorough analysis of the key characteristics – commissioning country, installed capacity, number of turbines, water depth, project area, distance to shore, transmission technology and investment cost – of the commissioned and under construction European OWPs Furthermore, the current status of the several countries outside of Europe was also investigated The analysis revealed that the European offshore wind power grew on average 361% yearly since 2001 Currently, there are 7748 MW installed and 3198 MW under construction distributed among 76 OWPs situated in European waters These projects are spread among ten countries, with the highest share of offshore projects belonging to the northern European countries The UK has 46% of the total installed European offshore wind capacity with 26 projects, Germany ranks second with 16, while Denmark is third with 13 projects These countries constitute 88% of the European offshore capacity The analysis also showed that, although the installed capacity of the OWPs is growing, the projects׳ area is not increasing at the same pace due to the release of turbines with higher rated capacities which allow projects to increase their power nameplate without proportionally increasing the number of turbines The average distance to shore and the water depth are both increasing throughout the years Although the average investment cost per project is rising with the higher distances to shore and water depths, the multi-GW plans of the northern European and Asian countries indicate that the industry will continue to grow The European Union targets of having 40 GW of offshore wind capacity deployed by 2020 in Europe and 150 GW by 2030 may represent plausible scenarios since the required growth is below the European

Impact of HVDC Transmission System Topology on Multiterminal DC Network Faults

Abstract: This paper compares how a dc fault affects a multiterminal dc (MTdc) network depending on the HVDC transmission system topology. To this end, a six-step methodology is proposed for the selection of the necessary dc fault protection measures. The network consists of four voltage-source converters converters radially connected. The converters natural fault response to a dc fault for the different topologies is studied using dynamic simulation models. For clearing of the dc faults, four different dc breaker technologies are compared based on their fault interruption time, together with a current direction fault detection method. If necessary, the converters are reinforced with limiting reactors to decrease the peak value and rate of rise of the fault currents providing sufficient time for the breakers to isolate the fault without interrupting the MTdc network operation. The study shows that the symmetric monopolar topology is least affected by dc contingencies. Considering bipolar topologies, the bipolar with metallic return exhibits better fault response compared to the one with ground return. Topologies with ground or metallic return require full semiconductor or hybrid breakers with reactors to successfully isolate a dc fault.

Impact of HVDC transmission system topology on multiterminal DC network faults

Abstract: This paper compares how a dc fault affects a multi-terminal dc (MTdc) network depending on the HVDC transmission system topology To this end, a six-step methodology is proposed for the selection of the necessary dc fault protection measures The network consists of four voltage-source converters converters radially connected The converters natural fault response to a dc fault for the different topologies is studied using dynamic simulation models For clearing of the dc faults, four different dc breaker technologies are compared based on their fault interruption time, together with a current direction fault detection method If necessary, the converters are reinforced with limiting reactors to decrease the peak value and rate of rise of the fault currents providing sufficient time for the breakers to isolate the fault without interrupting the MTdc network operation The study shows that the symmetric monopolar topology is least affected by dc contingencies Considering bipolar topologies, the bipolar with metallic return exhibits better fault response compared to the one with ground return Topologies with ground or metallic return require full semiconductor or hybrid breakers with reactors to successfully isolate a dc fault

Multiline Breaker for HVdc Applications

Abstract: This paper presents a breaker arrangement concept, the multiline breaker (MLB), for the protection of multiterminal high voltage dc (MTdc) networks Based on the design of a hybrid breaker, the MLB is an economically attractive solution for the protection of multiple dc lines in nodal connection using a single main breaker path By using commutation units, the MLB directs the fault current through the main breaker in a unidirectional way, irrespective of the fault location Hence, this study presents the design requirements for the MLB, regarding both hardware and control, and evaluates its operation within a grid For this reason, a four-terminal half-bridge multilevel modular converters-based MTdc grid in radial configuration was used and pole-to-ground dc fault conditions were investigated The dc fault response of the grid with one MLB at the central node is compared to the respective response of the grid when one hybrid breaker is employed at each dc line The simulations show that the MLB is feasible and that the overall MTdc grid fault response for the two protection systems is very similar As a result, the design advantages of the MLB make it a promising solution for the dc fault isolation in MTdc grids

Steady-State Loss Model of Half-Bridge Modular Multilevel Converters

Abstract: Lesnicar and Marquardt introduced a modular multilevel converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steady-state model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steady-state operation. The proposed model was compared to a loss model developed by Marquardt. Both models presented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system, in the overall efficiency of the MMC. To validate these new additions, the proposed steady-state model was compared to a dynamic model. Once again, the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.

DC Fault Detection and Location in Meshed Multiterminal HVDC Systems Based on DC Reactor Voltage Change Rate

Abstract: The change rate of the dc reactor voltage with predefined protection voltage thresholds is proposed to provide fast and accurate dc fault detection in a meshed multiterminal HVDC system. This is equivalent to the measurement of the second derivative of the dc current but has better robustness in terms of electromagnetic-interference noise immunization. In addition to fast dc fault detection, the proposed scheme can also accurately discriminate the faulty branch from the healthy ones in a meshed dc network by considering the voltage polarities and amplitudes of the two dc reactors connected to the same converter dc terminal. Fast fault detection leads to lower fault current stresses on dc circuit breakers and converter equipment. The proposed method requires no telecommunication, is independent of power-flow direction, and is robust to fault resistance variation. Simulation of a meshed three-terminal HVDC system demonstrates the effectiveness of the proposed dc fault detection scheme.

Assembly HVDC Breaker for HVDC Grids With Modular Multilevel Converters

Abstract: The modular multilevel converter (MMC) with half-bridge submodules (SMs) is the most promising technology for high-voltage direct current (HVDC) grids, but it lacks dc fault clearance capability. There are two main methods to handle the dc-side short-circuit fault. One is to employ the SMs that have dc fault clearance capability, but the power losses are high and the converter has to be blocked during the clearance. The other is to employ the hybrid HVDC breakers. The breaker is capable of interrupting fault current within 5 ms, but this technology is not cost effective, especially in meshed HVDC grids. In this paper, an assembly HVDC breaker and the corresponding control strategy are proposed to overcome these drawbacks. The assembly HVDC breaker consists of an active short-circuit breaker (ASCB), a main mechanical disconnector, a main breaker, and an accessory discharging switch (ADS). When a dc-side short-circuit fault occurs, the ASCB and the ADS close immediately to shunt the fault current. The main breaker opens after a short delay to isolate the faulted line from the system and then the mechanical disconnector opens. With the disconnector in open position, the ASCB opens and breaks the current. The proposed breaker can handle the dc-side fault with competitively low cost, and the operating speed is fast enough. A model of a four-terminal monopolar HVDC grid is developed in Power Systems Computer Aided Design / Electromagnetic Transients including DC, and the simulation result proves the validity and the feasibility of the proposed solution.

Trends of offshore wind projects

Abstract: The aim of this paper is to present the current status of the offshore wind industry and to identify trends in Offshore Wind Projects (OWPs) This was accomplished via a thorough analysis of the key characteristics – commissioning country, installed capacity, number of turbines, water depth, project area, distance to shore, transmission technology and investment cost – of the commissioned and under construction European OWPs Furthermore, the current status of the several countries outside of Europe was also investigated The analysis revealed that the European offshore wind power grew on average 361% yearly since 2001 Currently, there are 7748 MW installed and 3198 MW under construction distributed among 76 OWPs situated in European waters These projects are spread among ten countries, with the highest share of offshore projects belonging to the northern European countries The UK has 46% of the total installed European offshore wind capacity with 26 projects, Germany ranks second with 16, while Denmark is third with 13 projects These countries constitute 88% of the European offshore capacity The analysis also showed that, although the installed capacity of the OWPs is growing, the projects׳ area is not increasing at the same pace due to the release of turbines with higher rated capacities which allow projects to increase their power nameplate without proportionally increasing the number of turbines The average distance to shore and the water depth are both increasing throughout the years Although the average investment cost per project is rising with the higher distances to shore and water depths, the multi-GW plans of the northern European and Asian countries indicate that the industry will continue to grow The European Union targets of having 40 GW of offshore wind capacity deployed by 2020 in Europe and 150 GW by 2030 may represent plausible scenarios since the required growth is below the European

A Transient Voltage-Based DC Fault Line Protection Scheme for MMC-Based DC Grid Embedding DC Breakers

Abstract: Fast and reliable DC fault detection is one of the main challenges for modular multilevel converter (MMC) based DC grid with DC circuit breakers (DCCBs). This paper extracts the high-frequency components in transient voltages by wavelet transform and proposes a fault identification method based on the difference of square of transient voltages to identify the faulted lines for DC grids using overhead lines. Meanwhile, a faulted pole discrimination method based on the difference between the change of positive and negative pole voltages is presented. A line protection scheme including detection activation, fault identification, faulted pole discrimination, and post-fault re-closing is designed. Using only the local measurements, the scheme can realize the protection of the whole line without communication and has the capability of fault resistance endurance and anti-disturbance. The proposed method is tested with a four-terminal MMC-based DC grid in PSCAD/EMTDC. The selection methods of threshold values are presented and the impact of DCCB operation on the reliability of DC fault protection is analyzed. Simulation results verify the fast detection and reliability of the designed DC line protection scheme.

The Alternate Arm Converter: A New Hybrid Multilevel Converter with DC-Fault Blocking Capability

Abstract: This paper explains the working principles, sup- ported by simulation results, of a new converter topology intended for HVDC applications, called the alternate arm converter (AAC). It is a hybrid between the modular multilevel converter, because of the presence of H-bridge cells, and the two-level converter, in the form of director switches in each arm. This converter is able to generate a multilevel ac voltage and since its stacks of cells consist of H-bridge cells instead of half-bridge cells, they are able to gen- erate higher ac voltage than the dc terminal voltage. This allows the AAC to operate at an optimal point, called the “sweet spot,” where the ac and dc energy flows equal. The director switches in the AAC are responsible for alternating the conduction period of each arm, leading to a significant reduction in the number of cells in the stacks. Furthermore, the AAC can keep control of the current in the phase reactor even in case of a dc-side fault and support the ac grid, through a STATCOM mode. Simulation results and loss calculations are presented in this paper in order to support the claimed features of the AAC.