Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen

 
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
Institute for
High Voltage Technology
Review 2017
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
Key Figures of IFHT

Four Research Areas                        97 Employees                                   More than 90 Student Assistents
  Electrical Equipment and Diagnostics        74 Research Associates                        Mentoring of Experiments
  Switchgear and DC Technologies           	20 Technical & Administrative                  Preparation of Data
  Sustainable Distribution Systems            Employees
  Sustainable Transmission Systems            3 Visiting Lecturers from Industry

Facilities & Testing Center

High Performance Cluster for Fast          Testing Center: “Center for Grid               Laboratory & Testing Facilities
and Parallelized Simulations               Integration and Storage Technologies”          	High Voltage Laboratory
	Owning 500 Processor Cores with          	3.000 m² Laboratory with more than           	Medium Voltage Laboratory
  4.5 TB RAM in the High Performance          4 MW Power Rating                           	Circuit Breaker
  Cluster of the IT Center at RWTH         	Flexible Distribution Grid (10 kV/0,4 kV)    	Partial Discharge Diagnosis
  Aachen University                           with Real-World Assets and own              	Characterization of Electric Insulation
  IFHT-Server for Development Work with      Information, Communication & Control           Materials
   70 Processor Cores and 768 GB RAM          Room Technology                             	Climat Test Chamber
                                           	Research in the Field of Grid Integration,
                                              E-Mobility, IT-Security, …

Projects

More Than 50 Research and                  7.7 Mio. € Third-Party Fundings                International Activities
35 Services Projects                          4,8 Mio. € Publicly Funded Research         	International Collaborations
  Collaborative Research                      2,9 Mio. € Commissioned Research            	International Projects
  Fundamental & Supporting Research                                                       	EU Research
  Asset- & Material Testing
  Scenario Analysis
  Power Grid Studies                                                                                                                   Institute for
Teaching                                                                                                                               High Voltage Technology
    eiπ+1=0
                                                                                                                                       Review 2017
13 Lectures                                More than 750 Positions                        161 Degree Theses
   High Voltage Engineering                in Practical Courses                           	Bachelor and Master Theses
   Components of Energy Technology            Fundamental Practical Courses               	Broad Range of Topics
   HVDC                                       Power Engineering Practical Courses         	Reference to Projects
   Cross-Sectoral Topics                      Power Engineering Seminars
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
Content
              04   Editorial                                                                                 66  Department Sustainable Transmission Systems
                                                                                                             68  Voltage Stability in Electrical Transmission Grids
                                                                                                             70	Impact of Considering 110 kV Grid Structures on the Congestion Management
                                                                                                                 in the Transmission Grid
                                                                                                             72  Coordination of Reactive Power Compensation Systems in the Transmission Grid
              06   The IFHT - Brief Profile                                                                  74  Placement of Phase Shifting Transformers
              08   Key Activities                                                                            76  ESDP+ (Project Report)
              09   Board of Directors                                                                        77  Configuration of Bidding Zones (Project Report)
              10   In the limelight: Our staff                                                               78  Publications
              12   Research Areas and Organizational Structure
              14   Future Field “Digital Energy”

                                                                                                             80      Doctorates

              20   Research and Projects
              22   Department Electrical Equipment and Diagnostics
              24   Production Monitoring in the Cable Industry
              26   Test of Insulation Materials                                                              90      Infrastructure and Tools
              28   Intended Island Operation in Distribution Grid Structures                                 93      Grid Integration and Critical Infrastructure
              30   AiF XLink (Project Report)                                                                94      DCLab
              31   FitTherm (Project Report)                                                                 94      High Voltage Technology
              32   IBoTec (Project Report)                                                                   97      ProbFlow – Grid Analysis Using Probabilistic Power Flow Calculationn
              33   ENSURE (Project Report)                                                                   97      M²Q – Optimal Design of Multi-Carrier Energy Systems for City Districts
              34   Publications                                                                              98      IFHT-Toolchain

              36   Department Switchgear and DC Technologies
              38   Handling of Intersystem Faults
              40   Synthetic Test Circuit for Load Break Switches
              42   PROMOTioN (Project Report)                                                                100     Teaching and Networks
              44   Switching Arcs in Circuit Breakers (Project Report)                                       102     IFHT Alumni Partners and Supporters
              46   DCLab (Project Report)                                                                    104     Rogowski Events 2017
              47   Perception Threshold for Electric Fields (Project Report)                                 106     News in Teaching
              48   Auto-Reclosing Restart Concept for HVDC Systems                                           107     Student Project “Digital Energy Defence Laboratory”
              49   Research Campus “Flexible Electrical Networks” (Project Report)
              50   Publications

              52   Department Sustainable Distribution Systems
              54   Stability of Topological Power Plants                                                     108     Imprint
              56   Integration and Influencing Potentials of Rapid-Charging Stations in Distribution Grids
              58   Integration of Photovoltaic Generators
              60   Uncertainties in the Operational Scheduling and Control of Distributed Energy
                   resource Networks
              62   TrigFuse (Project Report)
              64   Publications

2 | Content                                                                                                                                                                                     Content | 3
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
This is again reflected in the figures. In the period under review,     to be converted to make it more suitable for today’s requirements.
                                                                                                                                                   12 completed dissertations, more than 160 completed bachelor            This means that we will gain an additional 1000 m², mainly office
                                                                                                                                                   and master theses, more than 70 research assistants, and more           space, and can thus bid farewell to our lack of space.
                                                                                                                                                   than 160 student assistants reflect further growth at the IFHT. In
Director of the Institute: Prof. Dr.-Ing. Armin Schnettler                                                                                         connection with the continued high level of third-party funding,        The IFHT spin-off “envelio” is developing even better than planned.
                                                                                                                                                   the high teaching performance, and the pleasing publication             The former IFHT entrepreneurs have won several innovation awards
                                                                                                                                                   activity, we were honored to once again come first in the faculty       and are in great demand. We will gladly help the young company

Editorial
                                                                                                                                                   ranking. Taking into account my “industrial internship”, which has      and make the close cooperation even more strategic. Let’s keep
                                                                                                                                                   now lasted for more than four years, this result makes me quite         our fingers crossed for “envelio”!
                                                                                                                                                   proud – and shows how capably and willingly all IFHT employees
                                                                                                                                                   perform their tasks. I consider this to be an excellent achieve-        The modernized layout of the annual report and the focused reports
Dear partners and friends of the Institute for High Voltage Technology,   mation and communication technology in conjunction with small            ment, and I would like to take this opportunity to express my           were very well received. With this in mind, we want to continue with
                                                                          generation units enables a decentralized sector-coupled energy           thanks.                                                                 this new approach and inform you of our ongoing and completed
We are on the path to an “all electric world” – the electrification of    supply with very high scaling effects, but also increasing complexity.                                                                           work in this informative and attractive manner. In addition, please
all sectors. Directly, for example, by replacing hydraulic and me-        Both paths require a completely different implementation and at the      Our cooperation with the Fraunhofer Institute for Applied Informa-      continue to visit our homepage regularly and contact us personally,
chanical components and drives with highly efficient and low-main-        same time a systemic integrated approach. The questions of supply        tion Technology (FhG FIT) is developing dynamically. It is becoming     which I still see as the guarantee of a successful cooperation. We
tenance electric motors. A key example of this is electromobility,        security and supply reliability in combination with economic efficien-   increasingly apparent that the close coordination of content and        need your comments and feedback in order to continue to meet
which is now also being introduced in the aviation sector. Indirectly     cy and complexity are the foundation of our work at the Institute for    cooperation as well as the joint use of infrastructure and offices      your and our demands for a modern and future-oriented research
by replacing fossil and nuclear fuels with renewable energy sourc-        High Voltage Technology. Stable political framework conditions are       (“co-location”) was the right strategic decision and has even result-   unit.
es, especially wind and solar energy. The reduction in the produc-        extremely important in this context. The climate protection targets      ed in considerably closer synergy than expected. Several research
tion costs for wind and solar energy to meanwhile less than 2 US          agreed globally are increasingly gaining acceptance and becoming         projects have been jointly acquired and are already partly being        I would like to thank all the partners for their excellent and intensive
cent/kWh and the combination of wind and photovoltaic power               commercially viable – thanks in part to the groundwork laid in Ger-      implemented; many more are in detail development. We hope to            cooperation, without which the Institute for High Voltage Technology
supplies in climatically favorable regions create interesting business    many. Germany’s federal and state policies themselves are however        be able to report soon on further cooperations and major joint          would not be able to exist in its current form. Of course, I would like
potential for Power2X technologies.                                       showing signs of procrastination with regard to the Energiewende.        projects.                                                               to express my special thanks to the IFHT staff for their dedication
                                                                          In this way, we have created neither consistency nor stability, we do                                                                            to and success in both academic matters and nurturing the IFHT
We can thus observe a division of the energy transition into two          not serve as a role model, and we have certainly not achieved our        The renovation of the Rogowski Institute is progressing somewhat        “family”.
increasingly independent implementation paths. On the one path,           goals. I am pleased that German industry and academia, despite           more slowly. The planning is becoming more detailed, but unfor-
very large centralized renewable energy parks are being created           the often difficult framework conditions and financial situation, are    tunately I can’t see its implementation until the next big alumni       Kind regards,
that are directly integrated into the transmission systems, while at      working on a consistent implementation of the energy transforma-         meeting in the early summer of 2019. The first aim is to restore
the same time enabling the large-scale industrial use of electrical       tion and are thereby sending out a clear message for the future.         the Rogowski building to excellent condition with the relocation of
energy for sector coupling, especially Power2Gas/Fuel systems.                                                                                     the business premises to the first floor: the traditional home of the
This creates the economic basis for a new import/export energy            Against this background, the goals set for the Institute are high,       Institute’s management. I hope that at least this basic first stage
industry – a kind of new oil and gas era. On the other path, infor-       and the tasks are increasingly complex, but also highly attractive.      will be completed within 12 months. Subsequently, the annex is          Prof. Dr.-Ing. Armin Schnettler

4 | Editorial                                                                                                                                                                                                                                                                         Editorial | 5
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
The IFHT – Brief Profile
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
The Board of Directors: left to right: Dr.-Ing. Sebastian Wetzeler, Dr.-Ing. Ralf Puffer, Dr. phil. Regina Oertel, Christoph Müller M.Sc., Prof. Dr.-Ing. Armin Schnettler, Dr.-Ing. Michael Andres,
                                                                                                                                              Dipl.- Economist Norbert Hornd. Absent: Tobias Falke, M.Sc.

Key Activities
Vision & Mission Statement
                                                                                                                                              Board of Directors
The energy transition and the complete substitution of nuclear and fossil energy sources is perhaps the most important and most
complicated task of mankind. The associated transformation of the energy systems is highly interdisciplinary, complex, and of worldwide       The director of IFHT is Professor Dr.-Ing. Armin Schnettler. He is supported by his Deputy Directors Dr.-Ing. Ralf Puffer and Dr.phil. Regina
relevance, although regionally specific. The digitization also supports a quasi-complete electr(on)ification of all sectors and industries.   Oertel. The heads of the four research divisions are also members of the board: Dr.-Ing. Michael Andres, Dr.-Ing. Sebastian Wetzeler,
                                                                                                                                              Christoph Müller, M.Sc., and Tobias Falke, M.Sc.. Furthermore, Norbert Horndt, Chief Financial Officer is also a member of the mentoring
Against this background, the Institute for High Voltage Engineering (Rogowski Institute) aims at,                                             team.
  providing a qualitative, timely and comprehensive contribution to all relevant issues,
  offering a sustainable education and training program and providing outstanding graduates in the labor market, and
  being the internationally accepted and nationally preferred academic partner.

Our research concentrates on
  the physical modeling as well as the market and system design of future energy systems,
  the interpretation, analysis and operation of necessary infrastructure, and
  the development of basic knowledge and expertise on these systems.

Implementation is driven by
  personal competence, innovation, and focused research,
  transfer of professional expertise and graduates into practice,
  national and international collaborations, and
  education and training programs.

8 | The IFHT – Brief Profile                                                                                                                                                                                                                                                                                 The IFHT – Brief Profile | 9
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
The IFHT staff

In the limelight: Our staff
The IFHT employees are our most important resource. Without        Besides thrilling and challenging research areas, IFHT offers        The members of staff of IFHT:                                         Cora Petino; Prof. Dr. Gerhard Pietsch; Dr.-Ing. Ralf Puffer;
engaged and enthusiastic people, IFHT could not reach its am-      special personnel work-life-balance measures. It is not without      Dr.-Ing. Michael Andres; Hans Barrios Büchel; Sascha Bauer;           Prof. Mattias Quester; Andreas Roehder; Philipp Ruffing; Torsten
bitious strategic objectives in research and teaching. More than   reason that the IFHT is one of the institutes of the RWTH Aachen     Marvin Bendig; Reinhold Bertram; Daniel Beulertz; Maurice Book;       Schäfer; Jan-Lucca Schmitz; Ricarda Schmitz; Dr.-Ing. Joachim
200 staff members – including more than 60 scientific assistants   University with the highest number of working parents – it is        Renate Bosetti; Christina Brantl; Carola Cieslak; Moritz Cramer;      Schneider; Maximilian Schneider; Dr.-Ing. Armin Schnettler; Lars
and more than 100 students – are working on solutions for the      self-evident that flexible work time is part of our standard. Com-   Wilhelm Cramer; Michael Cremer; Stefan Erkens; Philipp Erlinghagen;   Schröder; Nicolas Schulte; Sven Schumann; Alexander Schwarz;
energy turnaround. These up-and-coming young scientists are        pensation for work is offered by various sport events organized      Tobias Falke; Hartmut Frank; Marco Franken; Henning Frechen;          Seiler, Bernd; Simon, Sandor; Soppe, Bastian; Dr.-Ing. Torsten Sowa;
supported by highly experienced teams in the domains of con-       by the employees themselves, such as football, sailing, or the       Tobias Frehn; Felix Glinka; Matthias Heidemann; André Hoffrichter;     Stoffels, Marius; Stumpe, Maximilian; Walter Taeter; Christian
trolling, administration, EDP, and the workshop.                   professional Institute’s band.                                       Norbert Horndt; Daniela Janser; Norbert Jeß; Mathias Knaak;           Tappel; Doris Taufenbach; Nicolas Thie; Marc Trageser; Philipp
                                                                                                                                        Pascal Köhn; Thomas Krampert; Tom Kulms; Marcel Kurth;                Tünnerhoff; Timo Valter; Maria Vasconcelos; Michael Ksoll; André
                                                                                                                                        Walter Logen; Volker Lontzen; Janek Massmann; Ann-Kathrin             Wagner; Ralph Wegner; Dr.-Ing. Sebastian Wetzeler; Michael Weuffel;
                                                                                                                                        Meinerzhagen; Marian Meyer; Moritz Mittelstaedt; Benedikt Mölders;    Dominik Willenberg; Sebastian Winter; Tilman Wippenbeck; Lothar
                                                                                                                                        Prof. Dr. Klaus Möller; Robert Möller; Artur Mühlbeier; Christoph     Wyrwoll; Guido Xhonneux; Hannelore Zakowski
                                                                                                                                        Müller; Aleksandra Nikolic; Moritz Nobis; Dr. phil. Regina Oertel;

10 | The IFHT – Brief Profile                                                                                                                                                                                                                        The IFHT – Brief Profile | 11
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
Research Areas and
Organizational Structure
The IFHT is structured into four research areas in the field of energy   Sustainable Distribution Systems
technology.                                                              The research department Sustainable Distribution Systems focuses                                                                                   Director
                                                                                                                                                                  Deputy Director                                                                                       Deputy Director
                                                                         on the development of holistic solutions for the market and grid                                                                       Prof. Dr.-Ing. Armin Schnettler
                                                                                                                                                                 Dr. phil. Regina Oertel                                                                                Dr.-Ing. Ralf Puffer
Electrical Equipment and Diagnostics                                     integration of distributed energy resources (DER). This includes
The research topics of the department range from insulation mate-        the development of optimal grid operation strategies for DER and
rials over the electrical equipment of distribution and transmission     flexibilities as well as the conceptualization of novel methods for
grids to measurement, communication, and monitoring technologies         optimal grid planning and operation of distribution grids. The deve­                                        Electrical Equipment           Switchgear and DC                  Sustainable                     Sustainable
for critical infrastructures. The department is characterized both       lopment of dynamic grid and component models for the analysis                   Operations
                                                                                                                                                                                       and Diagnostics                Technologies                Transmission Systems            Distribution Systems
by an extensive test infrastructure for experimental research and        of protection and stability aspects is also part of the scope. Apart
by the combination of deep theoretical understanding of physical         from a long-term experience in the field of optimization and simu­
processes with an applied implementation in primary and secondary        lation, an extensive laboratory with various assets is available for            Controlling                  Head of Department           Head of Department              Head of Department             Head of Department
equipment.                                                               experimental foundation and verification.                                      Norbert Horndt                Dr.-Ing. Michael Andres     Dr.-Ing. Sebastian Wetzeler        Christoph Müller                 Tobias Falke

Switchgear and DC Technologies                                           Sustainable Transmission Systems
The research department Switchgear and DC Technologies con-              The research in the department Sustainable Transmission Systems                                             Cables, Overhead Lines           DC Control and              Stationary Grid Analysis            Distributed
                                                                                                                                                    Human Resources
tributes to the safe and reliable operation of our present and future    focuses on modeling, simulation and assessment of the sector-­                                              and Insulation Systems               Protection              and System Assessment             Energy Systems
                                                                                                                                                    Dr. phil. Regina Oertel
                                                                                                                                                                                       Dr.-Ing. Tobias Frehn         Dr.-Ing. Cora Petino             André Hoffrichter             Maria Vasconcelos
electrical power grids. The research areas include both technical        coupled European energy system from the transmission grid
requirements for switchgear, the development of minimally invasive       perspective and its stability. All investigations are based on self-­                                         Components and                   AC and DC                                                    Grid planning
diagnostic procedures, and the substitution of sulfur hexafluoride.      developed methods and models for holistic energy system analysis.               Controlling                                                                                 System Stability
                                                                                                                                                                                     Secondary Equipment                Switchgear                                                   and Operation
Further, the department works on the integration of DC systems           Central research interests cover the market behavior and power                 Norbert Horndt                                                                               Janek Massmann
                                                                                                                                                                                         Benedikt Klaer               Thomas Krampert                                                 Marcel Kurth
into existing grid structures and the control of errors in DC systems.   plant operation considering sector-coupling and the expansion
To answer the resulting questions, extensive experimental facilities,    of renewable energies. The impacts on the transmission grid are                Test Center/
                                                                                                                                                                                                                                                                                 Protection and Stability
e.g. synthetic test circuits, are available. The theoretical analysis    under investigation by means of realistic and novel grid operation               Services
                                                                                                                                                                                                                                                                                    Reinhold Bertram
                                                                                                                                                   Dr.-Ing. Michael Andres
and modeling of physical processes is supported by a wide range          strategies. The need for grid expansion is determined by optimi-
of simulative investigations.                                            zation and heuristic methods. Another focus is the development of
                                                                         methods for assessing system stability and the implementation of
                                                                         time-domain simulations for large-scale dynamic systems.                Organizational structure

                                                                                                                                                 The main focus of the research areas can be subsumed under the                  a wide range of lab and software equipment is available. Furthermore,
                                                                                                                                                 slogan: “From material over components to the energy system”.                   self-developed software tools can be used for the analysis of the
                                                                                                                                                                                                                                 system and market behavior for e.g. applied sciences.
                                                                                                                                                 The research is supported by the Human Resources and Financing
                                                                                                                                                 teams. The team of the secretary’s office ensures a smooth                      Second, the Master Internship Office of the Faculty of Electrical
                                                                                                                                                 operation of the business. The IT Division – without which neither              Engineering and Information Technology is currently located in
                                                                                                                                                 research nor administration would be possible – ensures not only                the IFHT. There, master students are advised on possibilities and
                                                                                                                                                 a stable IT infrastructure but also advises young researchers in                procedures regarding an internship in the industry. Reports of the
                                                                                                                                                 selecting necessary tools for research tasks. Prototypes and                    internships, which students have to provide, are also examined
                                                                                                                                                 special parts for test benches are produced by the mechanical                   by technical experts at IFHT. Last but not least, the students are
                                                                                                                                                 workshop using different materials such as plastics, non-ferrous                advised on how to take full advantage of their internship.
                                                                                                                                                 metals, and wood. The multiple electrical tasks are taken on by
                                                                                                                                                 the electrical workshop.

                                                                                                                                                 Two other areas are of great importance. First, the existing technical
                                                                                                                                                 infrastructure. In the areas of Grid Integration and Critical Infra-
                                                                                                                                                 structure, DC Technologies, and Classical High Voltage Technology,

12 | The IFHT – Brief Profile                                                                                                                                                                                                                                                The IFHT – Brief Profile | 13
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
Control room in the Center for Grid Integration of the Institute for High Voltage Technology

Future Field “Digital Energy”
Planning, optimization, operation and security of energy supply grids in
the context of digitization

“Digital energy“ is understood by the Institute for High Voltage                               The research focus is on applied innovation approaches which       data (safety/security), the implementation-oriented, high-preci-     these conditions can the complexity of sector-coupling energy
Technology as the next step in the interaction between informa-                                serve to embed digital concepts into existing methods, tech-       sion digital imaging of real electrical equipment and systems for    and industry concepts be fully represented and integrated in
tion and communication technology and the present energy sup-                                  nologies and systems. In this context, technical capabilities,     their planning and operation (Digital Twins, Autonomous Energy       energy systems.
ply systems. The aim is to create the most seamless symbiosis                                  economic potential and environmental sustainability need to be     Systems & Asset Management), and the development and prac-
possible of the digital and real worlds. Such a symbiosis should                               significantly expanded.                                            tical validation of innovation concepts and technologies in real     Therefore, the IFHT participates as an energy technology and
give rise to the interdisciplinary solution to current and future                                                                                                 test environments (Verification in Lab).                             system expert in establishing an interdisciplinary research
societal challenges in the areas of climate protection and secure                              From the point of view of energy supply, the key topics are the                                                                         cooperation with the Fraunhofer Institute of Applied Information
energy supply as well as to an increase in economic potential                                  inclusion, structuring, and utilization of digital energy system   The topics can not be considered individually, but require a spa-    Technology (FIT), the Fraunhofer Institute for Communication,
through market optimization in the energy, environmental, infor-                               information for all stakeholders (data management & usability),    tially close and interdisciplinary research collaboration between    Information Processing and Ergonomics (FKIE), and the Re-
mation and communication industries.                                                           ensuring the IT security of energy systems and safety of their     different university, research and industrial partners. Only under   search Center for Finance & Information Management (FIM).

14 | The IFHT – Brief Profile                                                                                                                                                                                                                                              The IFHT – Brief Profile | 15
Institute for High Voltage Technology - Review 2017 - (IFHT), RWTH Aachen
users can actively market or cover their energy without the need         systems, the described research questions must be accompa-
                                                                                                                                                  for an intermediary. Traditional tasks of utilities are disruptively     nied by an analysis of the legal-regulatory framework. Here, the
                                                                                                                                                  influenced. At the same time, greater interaction between the            compatibility test with the current framework conditions and the
                                                                                                                                                  energy and IT sectors offers utilities the possibility to act as a       derivation of potential further developments represent central is-
                                                                                                                                                  provider of additional digital value-added services (e.g. platform       sues. The IFHT participates for this purpose in various research
                                                                                                                                                  operators, dynamic pricing, etc.). Finally, the mentioned concepts       initiatives.
                                                                                                                                                  also represent the possibility for grid operators to assume a more
                                                                                                                                                  proactive role. For example, imminent capacity bottlenecks could be      Cornerstone of digitalization: “Secure Information and
                                                                                                                                                  prevented by timely demand of flexibility or incentive mechanisms.       Communication Technologies”
                                                                                                                                                                                                                           The fundamental change in the electricity supply goes hand
                                                                                                                                                  The creation of well-founded statements on the potential and             in hand with an increased automatization and integration of
                                                                                                                                                  the effects of such concepts needs research, development and             communication systems of all energy system stakeholders (e.g.
                                                                                                                                                  field tests. For example, the development of an information tech-        transmission & distribution grid operators, virtual power plant
                                                                                                                                                  nology platform for P2P trading and exchange of digital services         operators, meter operators, industry or manufacturers). This
                                                                                                                                                  could shed light on how business benefits can be tapped by local         increases complexity on a technological level and a process
                                                                                                                                                  transactions and what concrete effects this will have on grid opera-     engineering level. Also, the interaction between information and
                                                                                                                                                  tion and utilities’ and grid operators’ understanding of their role.     communication technology and the primary grid operation
                                                                                                                                                                                                                           increases. As a result, failures or interventions at the ICT level
                                                                                                                                                  Blockchain in power engineering and economics                            can increasingly have a direct impact on physical grid operation.
                                                                                                                                                  In the context of the decentralization of energy supply systems,
                                                                                                                                                  local, regional optimization of energy consumption is gaining            For this reason, the operational and information technology for
                                                                                                                                                  importance. Individual supply areas strive for an increase in local      energy systems is becoming an extremely attractive target for
                                                                                                                                                  resource allocation for economic and network-related reasons. To         cyber-attacks. Organized IT attacks on industrial and critical
                                                                                                                                                  ensure the safe and reliable operation of energy supply systems,         infrastructures are often multi-level and usually have long obser-
                                                                                                                                                  network operators must provide network-oriented services that            vation periods for gaining information in the context of Advanced
Research Department “Digital Energy”                                                                                                              anticipate the interactions between market and power grid (e.g.          Persistent Threats (APT). Based on coordinated information
                                                                                                                                                  oriented to traffic light functions). These innovations, realized with   retrieval, deterministic traffic in typically static networks enables
                                                                                                                                                  digital technologies, face a variety of challenges (coordination,        the planning of complex, distributed, and synchronized attack
Effects of sector coupling                                             the current energy systems. The German law for the digitization of         compatibility, secure and transparent processes, reliability, infor-     vectors.
Against the global background of energy policy goals, an increas-      the Energiewende (so-called Gesetz zur Digitalisierung der Energie-        mation technologies, etc.).
ing decentralization of the electricity supply system can be ob-       wende) creates the first standardized interfaces which go beyond                                                                                    In close cooperation with the Fraunhofer FKIE and the Fraunhofer
served. Large-scale power plants are increasingly being replaced       the digital recording of operational and accounting-­relevant data.        On the research side, therefore, one goal could be to develop            FIT, the IFHT is pursuing the goal to “develop technologies, con-
by a larger number of smaller, distributed generation units. At        With this first step, the development of local information platforms for   a local blockchain platform for P2P commerce and digital servic-         cepts and methods for the detection, prevention and reaction to
the same time, the electrification of the heat and mobility sector,    automated processing of digital services is possible in the medium         es. That includes on the one hand the implementation of the              IT attacks and IT failures for all energy system stakeholders”. The
in particular in the form of heat pumps and charging infrastruc-       term. These include, among others, the billing of charging processes       innovative business models and services that can be realized             aim is not the “greenfield” development of novel systems, but the
ture as well as the production of hydrogen and synthetic fuels,        at public charging stations as well as the dynamic design and billing      by and for companies and end customers. On the other hand,               applied research and development of approaches that can be
will increasingly generate additional electricity consumers on a       of network fees, taxes, and other charges. Thus, efficiency potential      new approaches to transaction processing and documentation               used in today’s and future supply infrastructures:
decentralized level. The following change in load and generation       for metering, billing and documentation can be unlocked. In addition,      are demonstrated. The technological choice of the block-chain
patterns affects the power flows and the capacity of the electrical    these platforms can be used to implement decentralized transaction         could demonstrate its suitability for use in the energy sector.          In the field of prevention, targeted measures to prevent IT security
transmission and distribution grids. This therefore represents a       and energy supply systems (peer-to-peer energy trading).                   The partial replacement of intermediaries, the partial automation        incidents are being researched. This includes development of
changed situation for network planning and operation.                                                                                             of processes and the implementation of a distributed database            measures for testing, acceptance and hardening of systems and
                                                                       The implementation of these concepts requires close cooperation            structure have massive potential for disrupting existing processes       networks.
In the course of this system change, new stakeholders enter the        between the fields of energy and information technology. Thus,             and role understanding in the energy industry. Research should
energy market and try to create new business models and to exploit     high demands are placed on data protection and security, which             be follow a holistic approach, analyzing and testing the impact of       The goal of detection is the identification of IT security incidents.
the potential offered by a higher degree of digitization and auto-     can be ensured by new IT concepts such as blockchain. In                   blockchain-based processes at all relevant physical and infor-           Here, by means of continuous monitoring of the status of sys-
mation of the overall system. Some of these stakeholders are, for      addition, protective measures must be taken into account which             mation technology levels. Through this, opportunities and chal-          tems and networks, the time between the attack and its detection
example, virtual power plant operators (VPPs), with which distribut-   can prevent the systems from being manipulated (e.g. targeted              lenges of innovative business models and services for energy             should be minimized. Approaches in this area include network
ed generation units can be marketed in a joint network and used for    arrangement of critical system states). Blockchain is also a suitable      stakeholders can be taken into account. Furthermore, it would            monitoring, intrusion detection systems, security information and
energy system services. VPPs can thus make an important contri-        instrument for this as it is subject to a decentralized consensus          have to be analyzed how the resulting P2P trading platforms can          event management, honeynet and threat intelligence.
bution to the market and system integration of renewable energies.     procedure for the confirmation of integrity.                               be embedded in the existing electricity markets. In addition, the
                                                                                                                                                  influence on the distribution grid has to be investigated and new        Reaction deals with the actions after an IT security incident has
However, digitization of energy supply is not only an instrument for   This cross-sector development can lead to a completely new                 requirements for network operation have to be designed accord-           been detected. Here, as far as possible, the damage to the victim
solving problems. It also has the potential for enormous shifting in   definition of the role of each of many current stakeholders. End           ingly. In terms of the applicability of the developed concepts and       should be minimized, the approach of the attacker understood

16 | The IFHT – Brief Profile                                                                                                                                                                                                                                       The IFHT – Brief Profile | 17
Center for Grid Integration of the Institute for High Voltage Technology

and knowledge obtained for the attribution to the attacker. In this        together on a study for the BSI, which analyzes and presents            shape the development and research of technologies and methods
area, among other things, incident response, IT forensics, and             the current state of IT security in the critical infrastructure power   for the planning, operation, and security of energy supply infrastruc-
malicious software analysis are point of interest.                         supply (according to BSI-KritisV). The purpose of the study is to       tures in the context of digitization.
                                                                           evaluate the implementation of the provisions of sec. 8a para.
Reliable mobility, production, and energy supply form the back-            1 of the Act to Strengthen the Security of Federal Information
bone for prosperity, growth and peace in an industrial nation like         Technology (BSIG), the suitability of the industry-specific security
Germany. The necessary development of technologies, concepts               standards according to sec. 8a para. 2 BSIG and submitted
and methods for the detection, prevention and reaction to IT               evidence according to sec. 8a para. 3 BSIG. Furthermore, the                     Contact:
security incidents can only be successfully achieved in the close          study serves to support the assessment of the situation according                Dr.-Ing. Michael Andres
interdisciplinary cooperation of various research institutions.            to sec. 8b para. 2 BSIG and evaluation of operator reports of IT                 andres@ifht.rwth-aachen.de
                                                                           security incidents according to sec. 8b para. 4 BSIG.                            +49 241 80-49331
In this context, the IFHT has already participated in several
studies, such as the FNN study “Safe System Operation with                 Through its employees, innovative and practice-oriented research
ICT”. The Fraunhofer FKIE and the IFHT are currently working               topics, and interdisciplinary cooperation, the IFHT will continue to

18 | The IFHT – Brief Profile                                                                                                                                                                                               The IFHT – Brief Profile | 19
Research
and Projects
Medium Voltage Test Area with Climate Chamber

Department Electrical Equipment
and Diagnostics
Head of Department: Dr.-Ing. Michael Andres

The research topics in the “Electrical Equipment and Diagnostics”         Modeling, monitoring, and diagnostics of high and medium                components and their interdependencies with the electrical grid.        The research department “electrical equipment and diagnos-
department range from insulation materials over the electrical            voltage equipment in their respective environments are the main         In addition to the proof of function, different test procedures for     tics” is characterized by its comprehensive test equipment for
equipment in distribution and transmission grids to measurement,          research topics of the electrical equipment research. Every             the voltage regulating components are developed.                        experimental investigation as well as the connection of a deep
communication, and monitoring technologies used in critical infra-        essential component (overhead lines, cables, transformers,…) is                                                                                 theoretical understanding of the physical processes with the
structure.                                                                being researched, simulated, and experimented with. In the area         The integration of information and communication technology             implementation of primary and secondary equipment into electrical
                                                                          of overhead lines the topics range from the increase of transmis-       into critical infrastructure, like the power system, is one of the      grids.
The insulation systems research varies over a wide range. Funda-          sion capacity, e.g. through high temperature low sag technologies       main focuses of the department. Different simulation tools as well
mental research about electrical, thermal, mechanical, and chemical       or monitoring of overhead lines; to parallel runs of AC and DC          as laboratory equipment, like the center for grid integration which
properties of multi-functional, innovative (e.g. syntactic foam), and     systems; up to the investigation of the human perceptibility of         has its own SCADA system, are available for successful develop-
typical (e.g. XLPE) insulation materials are the focus of the research.   electrical fields. By electrical, mechanical, and thermal simulations   ment opportunities. An exemplary topic in this research area is
Furthermore, the practical scope of applications of different insula-     as well as lab experiments; these relations are investigated            the security of used information and communication technology.
tion materials for cables, overhead lines, isolators, and supercon-       and applied to the current research topics. Based on the analysis       The impact of the grid operation through an increasing account of
ducting equipment are under investigation. The development of             of insulation materials and electrical equipment, methods and           different information and communication technology with all future
solid and fluid insulation materials for applications under non-sinus­    procedures for the operational as well as the strategic asset           players (e.g. grid operators, virtual power plant operators or meter-
oidal stress are topics researched by the department. The subject         management of system operators is developed (e.g. asset simu-           ing operators) is also under investigation. Finally the development
area deals in depth with the dimensioning and characterization of         lations, condition assessment methods,…). The research of grid          of applied concepts and technologies are brought together to tap
different materials and their integration with electrical equipment.      integration experimentally investigates the performance of different    the potential of the digitalization of energy supply systems.

22 | Research and Projects | Department Electrical Equipment and Diagnostics                                                                                                                                 Research and Projects | Department Electrical Equipment and Diagnostics | 23
different material thicknesses in order to represent both medium                              the model assigns the correct degree of crosslinking class to a
                                                                                                                                                              and high-voltage cable insulation. Ultrasonic measurements are                                sample base on the ultrasonic data. In the industrial production
                                                                                                                                                              then performed on the samples, while varying the temperature                                  line, however, not all parameters are available with the same
                                                                                                                                                              between 25–75 °C to cover the estimated material temperature                                  precision as in the laboratory. In particular, precise knowledge of
                                                                                                                                                              range during industrial production. To characterize the influence                             temperature and layer thickness is a prerequisite for reliable classi-
                                                                                                                                                              of cross-linking on the acoustic material parameters, the ultra-                              fication. A final sensitivity analysis shows that, in the worst case,
                                                                                                                                                              sonic measurement data is analyzed in the time and frequency                                  an error in the layer thickness measurement of 50 µm already
                                                                                                                                                              domain. In addition to the sound velocity and sound impedance,                                leads to a critical misclassification. In this case, it is possible that
                                                                                                                                                              the attenuation and frequency response of the received signals                                an insufficiently cross-linked sample is evaluated as fully cross-
                                                                                                                                                              are evaluated. The analysis of the speed of sound shows that a                                linked.
                                                                                                                                                              distinction between cross-linked and uncross-linked samples is
                                                                                                                                                              possible in the range of typical production temperatures, since                               For industrial monitoring, continuous monitoring of the sound
                                                                                                                                                              the speed of sound decreases with increasing cross-linking                                    velocity as a single parameter is therefore preferred. Since under
                                                                                                                                                              (Figure 3). This correlation exists for both medium and high-voltage                          normal process conditions neither the temperature nor the
                                                                                                                                                              cables.                                                                                       geometry of the cable will change rapidly, the ultrasonic system
                                                                                                                                                                                                                                                            can be calibrated automatically at the beginning of production.
                                                                                                                                                                                                                                                            Due to the high pulse repetition rate of commercial measuring
Figure 1: Measurement setup to determine the degree of cross-linking                                                                                                                                                                                        systems, it is possible to record several thousand measured
                                                                                                                                                                                                                                                            values per meter of cable length produced. Thus, a sufficiently
                                                                                                                                                                                                                                                            large number of measured values are available for the reduction

Production Monitoring in the Cable Industry                                                                                                                                                                                                                 of measurement noise by averaging, and statistical methods can
                                                                                                                                                                                                                                                            also be used to evaluate the product quality. As an example,
Ultrasonic measurement of the degree of cross-linking of XLPE                                                                                                                                                                                               the mean value of the sound velocity can be entered in a quality
                                                                                                                                                                                                                                                            control chart, and a warning can be issued to the line manager if
                                                                                                                                                                                                                                                            predefined warning limits are exceeded. By knowing the temper-
Production monitoring today                                                          During the production process, the degree of cross-linking (DoC) is                                                                                                    ature and cross-linking degree dependencies, it is also possible
Modern medium and high-voltage cables are designed with a                            therefore checked by thermal expansion tests (hot-set tests) at the                                                                                                    to assess whether any deviation in the process is critical or not.
three-layer insulation system consisting of an inner and outer                       beginning and end of each production length. Since a hot-set test        Figure 3: Sound velocity of XLPE in dependence of the degree of cross-linking at a tempera-   Ultrasonic measurement technology has therefore proven to be
field controlling conductive layer and an insulation layer (Figure 2).               is a destructive measuring method, continuous monitoring of the          ture of 45 °C                                                                                 a suitable tool for qualitative monitoring of power cable produc-
                                                                                     cross-linking process is not possible. This means that local, but                                                                                                      tion.
                                                                                     critical fluctuations in the degree of cross-linking during production   Development of a non-destructive monitoring method
                                                                                     cannot be detected. A non-destructive measuring method would             The evaluation of the individual parameters shows that there is a
                                                                                     enable the manufacturer to continuously monitor the production           dependency of the acoustical material properties on the degree
                                                                                     process and react quickly to errors or changes in the degree             of cross-linking. However, the range, i.e. the difference between
                                                                                     of cross-linking. This could reduce scrap and thus production            uncross-linked and fully cross-linked samples, is small. For ex-                                       Project Acronym:
                                                                                     costs.                                                                   ample, the range for the sound velocity is approximately 15 m/s.                                       AiF XLink
                                                                                                                                                              This is a value that can still be resolved under laboratory condi-
                                                                                     Preliminary investigations on the measurability of the DoC               tions, but it is a challenge for an industrial monitoring process. In                                  Project Duration:
                                                                                     It is known that cross-linking of polyethylene alters the thermo-        a first step, a multivariate approach is therefore pursued in order                                    Jun. 2015 – Nov. 2017
Figure 2: XLPE insulated high-voltage power cable with aluminum conductor and wire   mechanical properties of the material. Furthermore, changes              to exploit the entire information content of the measurement
screen                                                                               in the mechanical properties of a material can be detected with          signals. Classification models are trained with different methods                                      Main Partner:
                                                                                     the help of ultrasonic measurements. It is therefore assumed that        of machine learning, which receive the various characteristics                                         FGH e.V.
The most widely used insulation material today is cross-linked                       ultrasound technique could be suitable for the non-destructive           of the measurement signal as input parameters. In addition to the
polyethylene (XLPE). In addition to its high electrical strength, it                 determination of XLPE’s degree of crosslinking. Ultrasound exam-         k-nearest-neighbor classification, decision trees and neural networks                                  Contact:
has excellent thermal properties. The cross-linking of the poly-                     inations in the laboratory can be used to determine the funda-           are investigated. In addition to sound velocity and attenuation as                                     Dr.-Ing. Sven Schumann
ethylene transforms the thermoplastic into a thermoset that does                     mental dependencies of the acoustic material parameters on               conventional input parameters, further signal features are extract-                                    schumann@ifht.rwth-aachen.de
not melt at higher temperatures and thus increases the ampacity                      the degree of cross-linking. In a second step, the parameters that       ed including, for example, the slope steepness of the frequency                                        +49 241 80-90270
of the power cable. Insufficient cross-linking can therefore have                    are most suitable for continuous monitoring are identified.              spectrum as a measure for the frequency-dependency of the
potentially serious consequences for the power cable as the                                                                                                   attenuation.
uncross-linked insulation system can melt in the event of an over-                   Within the scope of the project, XLPE samples with different
loaded line or under short circuit conditions. A deformation of the                  (defined) degrees of cross-linking are produced on a laboratory          The trained models are validated subsequently with a separate
coaxial design of the cable caused by excess temperature can                         scale. The specimens are classified into different classes, ranging      test data set. Depending on the model and parameter set, an
lead to an increased field stress in the insulation and, in the worst                from uncross-linked specimens (type A) to fully cross-linked             accuracy of classification > 95 % can be achieved for laboratory
case, to an electrical breakdown of the insulation system.                           specimens (type D). Test specimens are manufactured with two             measurements. This means that in more than 95 % of all cases

24 | Research and Projects | Department Electrical Equipment and Diagnostics | Research Report                                                                                                                    Research and Projects | Department Electrical Equipment and Diagnostics | Research Report | 25
Test of Insulation Materials
Test benches for the investigation of insulation materials at medium-frequency
voltages

The development of power electronic semiconductors enables                                                                                                    rectangular voltages. Due to the short switching time of the semi                       Relative permittivity as well as the dissipation factor may be
the use in equipment at increased voltages, power and variable                                                                                                conductive devices, such as IGBTs, high slew rates are achieved                         measured at voltages of up to 500 V in a frequency range
voltage forms. One possible area of application of semi con-                                                                                                  during zero crossing of the voltage. A high voltage is reached by                       between 50 Hz and 50 kHz. Guard ring arrangements are used for
ductive devices is in converters, which may be used at medium                                                                                                 a series connection of the IGBTs.                                                       liquid and solid insulation materials. A frequency weighted loss
voltage levels. Therefore, the AC/DC converters can be used to                                                                                                                                                                                        ratio can be defined as the product of relative permittivity, dissi-
integrate DC components into the existing AC grid at different                                                                                                The solid state Marx generator is made of 32 equal stages. A                            pation factor, and the frequency. The product is proportional to the
voltages. Additionally, a DC/DC converter for the transformation                                                                                              maximum output voltage at the device under test of 100 kV can                           frequency dependent losses and can be used for the evaluation
of voltage and the galvanic insulation for possible medium-voltage                                                                                            be reached by the serial and parallel connection of different stages.                   of the material dependent losses at each frequency.
DC grids may be constructed. For the coupling of DC systems                                                                                                   Compared to the first test bench, the breakdown voltage of the
and the AC medium-voltage grid, a rectifier has to be added,                                                                                                  insulation materials is measured by using a constant increase                           Breakdown voltage of insulation materials in the frequency range
which feeds the converter. In both cases, the converter is made                                                                                               of the effective output voltage form zero until the breakdown                           between 1 and 10 kHz can be determined with respect to the
of an inverter, a transformer, and a rectifier. The frequency of the                                                                                          occurs. Freewheeling diodes on each stage, which are connect-                           voltage shape with the first and the second test bench. Therefore,
transformer, which is part of the AC intermediate circuit, is higher                                                                                          ed anti-parallel to the IGBTs, protect the semiconductors against                       the influence of higher harmonics and high slew rates on the
than 50 Hz. For a reduced component size and an increased                                                                                                     damage coming from overvoltages.                                                        breakdown voltage can be investigated. The dielectric material
efficiency, the frequency of the intermediate circuit is chosen be-                                                                                                                                                                                   parameters may be used for the determination of the losses in
tween 1 and 10 kHz. The breakdown voltage of the transformer                                                                                                  Galvanic insulated sources and individual controlled stages enable                      the insulation material. This enables the evaluation of influences
insulation is unknown in this medium frequency range and has to                                                                                               the usage of the solid state Marx generator as a signal source for                      due to losses on the breakdown voltage.
be investigated. The investigations take place in association with                                                                                            the measurement of the breakdown voltage in a frequency range
the research project Forschungscampus FEN – „Flexible elek-                                                                                                   between 1 and 10 kHz. Figure 2 shows the bipolar solid state
trische Netze“ –. Transformer insulation, such as transformer oil      Figure 1: Test bench for the measurement of breakdown voltage at sinusoidal voltages   Marx generator.
and impregnated fibers, is tested at medium-frequency voltages.
The tests include the frequency dependent measurement of the           at sinusoidal voltages in the intended frequency range. The                                                                                                                             Projekt Acronym:
breakdown voltage at different voltage shapes, such as rectan-         breakdown voltage of the insulation material is measured by using                                                                                                                       FEN
gular and sinusoidal voltages.                                         a constant increase of the output voltage form zero until the
                                                                       breakdown occurs. A maximum output voltage of the test bench                                                                                                                            Project Duration:
Two different test benches are built up for the measurement of         of 100 kV can be reached. Thereby, the gradient of the effective                                                                                                                        Oct. 2014 – Sept. 2019
the breakdown voltage as a function of frequency and voltage           output voltage is 1 kV/s.
form. Therefore, the influence of frequency and voltage shape                                                                                                                                                                                                  Main Partners:
can be investigated separately from each other. Furthermore,           The breakdown voltage of insulating materials such as insulation                                                                                                                        RWTH Aachen University, Siemens AG,
one test bench for the estimation of the losses in the insulation      oil and resin impregnated fibers can be measured using the test                                                                                                                         Westnetz, Schaffner Deutschland, Infineon,
material is available. The test bench enables the measurement          bench. The test bench with the air coupled transformer is shown                                                                                                                         MR Maschinenfabrik Rheinhausen &
of the material and frequency dependent specific loss densities.       in figure 1.                                                                                                                                                                            additional partners

Test bench for the measurement of the breakdown voltage                                                                                                                                                                                                        Contact:
at sinusoidal voltages                                                 Test bench for the measurement of the breakdown voltage                                                                                                                                 Robert Möller, M.Sc.
Breakdown voltage at medium-frequency sinusoidal voltages is           at rectangular voltages                                                                                                                                                                 robert.moeller@ifht.rwth-aachen.de
measured by using a test bench, which is based on a power-­            For the measurement of the breakdown voltage in the medium-­                                                                                                                            +49 241 80-93032
electronic fed, air-coupled transformer. The primary and second-       frequency range, a test bench is constructed which is based on a                       Figure 2: Test bench for the measurement of breakdown voltage at rectangular voltages
ary winding is part of a separate resonance circuit to reduce the      Marx generator. A solid state Marx generator is produced when
amount of transmitted power.                                           the charge and discharge resistors and the spark gaps are                              Test bench for the determination of the dielectric material
                                                                       substituted by power electronic semiconductors. This topology                          parameters
The test bench frequency range is limited in a range between 1         enables the generation of high voltages with high slew rates.                          The breakdown of the insulation material may be influenced by
and 10 kHz by the Eigenfrequency of the secondary winding and                                                                                                 electrical breakdown as well as thermal breakdown caused by
the maximum input power. The output voltage is sinusoidal with         A galvanic insulated source is used with an additional conduc-                         thermal heating. The losses at higher frequencies can be measured
higher harmonics that can be neglected. Therefore, the test bench      tive path to build a voltage source which is capable of supplying                      with a test bench which offers the opportunity to determine the
is appropriate for the measurement of the breakdown voltage            the device under test with periodic medium-frequency bipolar                           frequency dependent relative permittivity and dissipation factor.

26 | Research and Projects | Department Electrical Equipment and Diagnostics | Research Report                                                                                                                  Research and Projects | Department Electrical Equipment and Diagnostics | Research Report | 27
Figure 1: Test bench with grid-forming battery inverters in the low-voltage laboratory of the IFHT                                                                            Figure 2: RLC load unit for the compensation of the active and reactive power balance and tuning of the resonance frequency

Intended Island Operation in                                                                                                                                                  the grid-forming inverters and by the interoperability between
                                                                                                                                                                              grid-forming and grid-tie inverters (interaction of voltage and cur-
                                                                                                                                                                                                                                                                            potential for the excitation of ROCOF (rate of change of frequency)
                                                                                                                                                                                                                                                                            relays in grid-parallel energy conversion systems. A low-frequency

Distribution Grid Structures                                                                                                                                                  rent sources). In this context, this interaction plays a decisive role
                                                                                                                                                                              in terms of the harmonic stability (excitation of resonances which
                                                                                                                                                                                                                                                                            gradient places higher demands on voltage stability in the island
                                                                                                                                                                                                                                                                            grid. As part of the research activities, requirements for parameters
Development of test procedures for the stable operation of island networks                                                                                                    impair proper operation) as grid forming components have an                                   and time constants of such characteristic curves are developed
                                                                                                                                                                              immediate influence on the voltage form and a reduced voltage                                 and transferred into test procedures for grid-forming and grid-tie
                                                                                                                                                                              quality in turn has an effect on grid-parallel systems.                                       inverters.
A consistently high reliability of the electrical energy supply is not                               an island formation is recognized. However, the stable operation         At present, the interference emission and immunity of inverters
guaranteed without the adaptation of grid operation concepts or net-                                 of island grids based on existing network structures and systems         in networks with reduced voltage quality and in island operation
work structures. As a possible measure to maintain supply reliability,                               requires that these systems remain reliably and stably connected         networks are scarcely studied and are not comprehensively
so-­called intended island grids are being tested to reduce system                                   to the grid under controlled conditions. One concept for this is         covered in test procedures. Therefore, the need for adaptation of
complexity in critical network situations or for power system restora-                               the deliberate influencing of detection methods. The use and             current test methods is examined and further developments are                                             Project Acronym:
tion after black-out events. In this case, the operation of an electrical                            combination of different methods as well as manufacturer-specific        evaluated which take into account intended island networks (e.g.                                          ENSURE
supply island in the public distribution grid (e.g. in low voltage), which                           implementations motivate experimental investigations to identify         reduced short-circuit power, inverters with grid-forming functionality)
is separate from the interconnected grid, takes place through the                                    influencing factors on the detection capability. Therefore, anti-­       in the testing of interference emissions and immunity and cover                                           Project Duration:
local balancing of generation and consumption at a regional level. For                               islanding methods are tested and analyzed by the emulation of            a wide spectrum of frequencies.                                                                           Oct. 2016 – Sept. 2019
this purpose, decentralized generation units combined with decen-                                    island networks in an own low-voltage laboratory at the Institute
tralized storage systems (e.g. battery storage systems for self-con-                                 for High Voltage Technology. These include both island grid              Interaction between components under consideration of                                                     Main Partners:
sumption optimization, electromobility) show increasing potential.                                   emulation through the use of bidirectional, grid-forming inverters       intended, inverter-based island grids                                                                     Karlsruhe Institute of Technology,
                                                                                                     from different manufacturers and power classes, as well as the           The current draft of the VDE application rule (AR-N 4105, June                                            RWTH Aachen, E.ON, TenneT
The operation of an electrical island, which is disconnected from the                                integration of ohmic, inductive, and capacitive load units into the      2017) addresses storage systems for the first time with regard to                                         TSO GmbH, Siemens AG, ABB
interconnected grid, requires the substitution of ancillary services                                 test grid. The latter make it possible to simulate an island grid        their integration into low-voltage networks with network supporting                                       AG & 17 additional partners
provided through power plants (e.g. voltage and frequency control)                                   by compensating the active and reactive power imbalances and             functionalities. The potential for controlled bidirectional power
by the functional scope of components within the island. In order                                    tuning the resonant frequency to a resonant circuit quality of Qf = 3    flow is raised by extending the power-frequency curve (P(f)) for                                          Contact:
to do so, inverter-coupled energy conversion systems can deliver a                                   for “household” battery inverters, based on the resonant circuit         the under-frequency range. In inverter-based island grids, there is                                       Sandor Simon, M.Sc.
key contribution. Requirements for the operating behavior and the                                    test according to DIN EN 62116.                                          no physically inherent link between frequency and power balance                                           simon@ifht.rwth-aachen.de
functionalities to be provided as well as methods for testing energy                                                                                                          due to the lack of synchronous generators. Therefore, it is useful                                        +49 241 80-49212
conversion systems are developed at the Institute for High Voltage                                   Harmonic stability                                                       for active power control to specify the frequency of grid-forming
Technology within the scope of the ENSURE project. Investigation                                     The increasing penetration of power electronic as well as capacitive     energy conversion systems via suitable characteristic curves (e.g.
focuses on islanding detection methods, aspects of harmonic stabil-                                  and inductive components (e.g. in passive filters) with simultaneous     f(P) and f(SOC: state of charge)). This form of power regulation
ity, and requirements on characteristic curves and parameters for                                    reduction of ohmic loads results in an increasing share of com-          by grid-forming, inverter-coupled energy conversion systems has
regulating the interaction of systems in off-grid operation.                                         ponents with non-linear U-I characteristics and high-frequency           not been extensively tested for use in distribution network struc-
                                                                                                     switching operations. This leads to impaired voltage and current         tures in island operation and has not been taken into account in
Islanding detection methods                                                                          quality and an increased potential to excite resonances. In inverter-­   test procedures. Initial investigations show various restrictions
Islanding detection methods currently implemented in inverter-­                                      based island grids without synchronous generators, stable                for possible characteristic curve parameters. For example, a fast
coupled energy conversion systems initiate disconnection when                                        operation is significantly influenced by the operating behavior of       frequency change by a grid-forming generator increases the

28 | Research and Projects | Department Electrical Equipment and Diagnostics | Research Report                                                                                                                                   Research and Projects | Department Electrical Equipment and Diagnostics | Research Report | 29
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