Keynote Speakers

With electromechanical devices as connectors and switchgear, the contact material used is a crucial component to fulfill technical and commercial requirements. With connectors and switches for information technology, contact surface layers with thicknesses in the µm range are used in very most cases. Due to arcing with switching operations in power engineering applications, thin layers are not sufficient – thus, contact material thicknesses ranging from some hundred µm up to some cm are applied. The present paper gives an overview regarding different contact material families for power engineering as silver/nickel, silver/refractory, copper/tungsten, silver/metal oxide, and silver graphite, including the different physical mechanisms leading to their specific switching behavior. On the background of climate change and measures to reduce greenhouse gas emissions, the generation and use of electrical power undergo remarkable changes. Thus, switching devices have to meet modified or new tasks as switching of highly energy-efficient electric motors, more demanding DC applications, and combinations of electromechanical and solid-state switching devices. This paper discusses possible consequences for contact materials to fit better to these changing requirements.

The growing demand for electrical energy and the limited resources of fossil fuels require an increased use of renewable energy sources (photovoltaic, wind turbines) combined with a low-loss energy transmission and distribution system. HVDC technology is increasingly being used in the high-voltage range with power electronic elements (IGBT, Thyristors). The same power electronic elements enabled the development of Hybrid Circuit Breakers, a technology that up to now proves to be a feasible solution for the switching process in HVDC meshed networks.

In low voltage systems, representing the main focus of this conference, DC low voltage networks and DC smart grids, capable of handling bidirectional energy flows, will become increasingly important. New applications can be found in PV systems, storage systems, computer centers, on-board networks, lighting technology and electro-mobility. A selective overview of the developments in those research areas, focusing on the switching devices, will be offered.

Powerful protection and switching devices for DC operating voltages up to 1500 V DC are required for the operation of these systems. The basic principles used by these devices will be overviewed and discussed.

An essential point in this development is represented by the requirements imposed by the international standards. Here, the safe visible galvanic isolation point plays an important role as described in IEC 60898 (Part 3) and UL 489 H. This typical characteristic fulfilled by an electromechanical switchgear, combined with the advantages of low power losses, robustness to electromagnetic fields (EMC), overcurrent and overvoltage resistance, will continue to make the electromechanical switchgear a necessary component of the electrical network in the future.

In the past decades, circuit breakers in medium and high voltage networks have been dominated by vacuum and SF6 gas technology, respectively. The increasing awareness of the high global warming potential of SF6 and the consequential increasing objection to use this technology have triggered substantial R&D-efforts to find environmental friendly alternatives. This presentation will give an overview on the challenges associated with finding alternative high voltage circuit breaker technologies and the recent advancements. In contrast to the harmonized and standardized use of SF6, the proposed and investigated alternatives are numerous and include various gases as well as vacuum. Pre-standardization initiatives (as for example the Cigre WG B3.45, D1.67, or A3.41) try to identify common grounds and suitable measures for comparison. Additional efforts comprise also an international round-robin test initiative comparing the electric strength of various alternative gas mixtures as well as experiments on vendor-independent switching devices comparing the interruption performance. One of the innovative “experimental tools” to investigate the interruption performance is a flexible pulsed current source with which sophisticated current shapes can be generated and which enables advanced tests, e.g. the determination of black-box parameters of switching arc for use in development tests. In addition, other example use cases for this flexible pulsed current source are detailed investigations of the safe operating area of power electronic devices or the pre-arcing and arcing phase of high-current fuses.

The speed and scope of change in the Automotive Industry has increased considerably and is now also influenced to a large extent by external forces. Electrification and digitization, within the vehicle and the surrounding environment, are having a significant impact on powertrain architectural design and its electromechanical components.
In addition to purely electric vehicles, hybrid architectures with 48 … 500Volt wiring systems will play an important role on the market. Besides high voltage requirements, continuous currents up to 500A and short circuit transients in range of 30kA might influence the design of electrical contacts and their electrical application environment. Therefore, the right balance of materials, weight, heat management and the associated costs is necessary for component dimensioning. It is critical that the effects of permanent, short-term and transient loads are considered from the outset. Thermal-electrical simulation methods can help to achieve an optimum design level.
One example is increasingly powerful batteries, designed for greater range. Power density goes up remarkably and continuous power as well short circuit energies needs to be considered to select or design suitable components. Batteries becoming a key element inside and outside the car and a complete ecosystem is required to manage energy demand and grid stability. Their behavior during driving operation differs greatly from the charging operation. This means that a clear distinction must be made between driving profiles and AC vs. DC charging.
The thermal design of the battery and its charging path including all its electromechanical components is a key factor that determines performance in driving and charging modes that can be an important competitive differentiator. The charging infrastructure and thus also the charging interface in the vehicle plays an increasingly important role for the acceptance of electromobility. In order to enable short charging times, featuring charging currents of up to 500 amps, with existing charging interfaces, the vehicle components must be upgraded in accordance with various international standards. Fast charging places the highest technical requirements on the HV connection technology.
The talk will highlight the necessary architectural adaptations and the consequences for electromechanics, keeping in mind the digital influences as well as the increased complexity of planning, development, production and operation of vehicles which must be economically feasible.

The global photovoltaic (PV) power capacity is growing exponentially. However, the undetected arc faults would pose a severe fire hazard to PV systems, so various advanced detection techniques have been proposed especially in the last few years. This talk presents a comprehensive review of state-of-the-art techniques for DC arc fault diagnosis in PV systems, and the development trend of future detection methods is also discussed.

Diagnosis methods viewed from physical and electrical signals of DC arc faults have been proposed for a few decades. Their capabilities and limitations are discussed, compared, and summarized in detail. By acquiring electromagnetic radiation and ultraviolet light characteristics of arc faults, diagnosis methods based on physical signals have the advantage of the accurate identification. However, these methods show limitations for large-scale PV systems due to the increasing interference factors in the exposed environment. Through signal processing methods such as fast Fourier transform, wavelet transform and statistic methods, much more works focus on diagnosis methods based on electrical signals. Recently, detection methods with good switching noise and system transition immunity have been introduced. For instance, the existing Db9-based features would cause nuisance trip for the arc fault detection in grid-connected PV systems. The Rbio3.1-based features are proposed to achieve better arc fault recognition ability.

Since the field testing is costly and time consuming, precisely modeling arc faults becomes more critical. Different types of DC arc fault models including physical-based arc model, V-I characteristic-based arc model and high-frequency variation arc model have been reviewed and compared.

In addition, future trends about PV arc faults diagnosis methods are outlined. It is predicted that facing more complex arc fault conditions, the data processing chip development and machine learning based classifier are of great significance to improve the detection accuracy of diagnosis methods. Also, the detection reliability of diagnosis methods would be significantly improved without increasing the computation time significantly.

Numerical simulations of gas discharges have long been considered too challenging for routine use in product development. There is a twofold reason for this: the complex physics involved and the lack for suitable software tools. The physical complexity requires us to be judicious in in the choice of models as we are constantly forced to compromise between speed and accuracy. The challenge is to find approximations good enough for specific applications and there will probably never be one universal simulation for arc discharges.

The lack of suitable software tools if partly due to lack of interest form software vendors and partly due to the difficulty of coupling the equations involved. Whereas the flow equations are best solved using a finite volume formulation, the electromagnetic equations are best solved using finite elements. Currently, the perfect algorithm only exists on paper.

Despite these difficulties, significant progress has been made in recent years. This paper tries to outline the state-of-art in simulations of electric arcs and gas discharges with a detailed discussion of the approximations made and their impact on convergence and accuracy. We emphasize that arc simulations, if correctly used and interpreted, are useful tools for product development today. In particular, simulations can deliver results that are only indirectly related to the arcing process, such as pressure buildup and mechanical stresses on enclosures.

In addition, we argue that a paradigm shift will be required to develop better software simulation tool. Rather than first developing theoretical models and implementing them, we need to start by establishing an efficient computational framework and fill it with details later. An efficient and parallelizable code is required to validate the simulations in rigorous manner.

The lecture will review 59 years (1961 – 2020) of measurement and analytical techniques that have enabled the further understanding of arc interruption and continual development of switches, relays and circuit breakers. The introduction of the high-speed oscilloscope in the early 1960’s, for the first time, made observation of current and voltage down to the nano-second level. This led to a better understanding of arc formation, arc interruption and arc erosion. The scanning electron microscope also introduced in the early 1960’s permitted the detailed study of arc erosion effects. The addition of x-ray analysis in the early 1970’s allowed a detailed analysis of elemental changes in the contact’s face. The development of advanced vacuum technology in the late 1960’s enabled introduction of the sealed-for-life, power, vacuum interrupter for high voltage distribution circuits. In the 1970’s electronic sensors began to replace the electro-mechanical sensors to control relays and circuit breakers. Integrated circuit technology then was increasingly introduced into these sensors. Today there are many relays and circuit breakers that can respond to a great many types of circuit conditions and determine the action to be taken. The personal computer (PC) first introduced in the 1980’s began a revolution in the engineer’s and scientist’s world. Who remembers secretaries, the written letter and the slide presentation etc.? The PC became so powerful that in the 1990’s relays and circuit breakers could be designed at the engineer’s desk top using 3-D drafting software. The introduction of finite element analysis (e.g. ANSOFT) and arc modeling software (e.g. FLUENT) has aided the advanced development of all switching devices. The MEMS (micro-electronic mechanical systems) switches were introduced in the late 1990’s. In the future switches, relays and circuit breakers will continue to be used to switch and isolate electrical circuits in spite of the inroads of power electronic devices. They will become more compact and will also become more intelligent as more advanced sensor technology is introduced. The vacuum interrupter, now the prevalent technology for 5kV t0 40,5kV circuits will start to dominate higher voltage circuits (72kV to 170kV) and perhaps the MEMS switch will find a commercial application!