**Preface to "Protection of Future Electricity Systems"**

One of the important areas in powers systems, one which is sometimes overlooked, is power system protection, which is a safety critical component of all electrical systems. Fast and reliable detection of abnormal conditions, as well as identification and prompt removal of the faulty component, help in preserving system integrity, and minimise potential negative impact on the rest of the grid. The consequences of a major failure of the transmission system protection, likely leading to system backout, are difficult even to imagine.

Therefore, there is a pressing need for innovation and a new long-term strategy in power system protection. We hope this Special Issue makes a useful contribution towards this goal. We present ten interesting papers covering a wide range of topics, all related to protection system problems and solutions.

**Adaptive protection:** An idea of adaptive protection, where relay settings are modified in response to changing system configuration or operating conditions, has been present in technical literature for quite some time. While in the past, its practical application was not perceived as critical, and was additionally limited by technological constraints, the development of numerical multifunctional relays accompanied by digital communications, as well as increased system fault level variability, has enabled adaptive protection to progress to practical applications. In this Special Issue, we include two papers which propose adaptive solutions for both high voltage transmission system and the distribution level microgrids.

**Protection of DC systems:** There are many situations when DC electricity systems are preferable to AC systems, especially when considering rapid advances in power electronic converter technologies and utilisation of energy sources which naturally produce DC power, such as photovoltaics or batteries. Both HVDC and LVDC systems are being developed and the protection of such networks has a separate set of challenges in terms of ultra-fast fault detection requirements and DC fault current breaking. Therefore, we are pleased to present four papers tackling various aspects of DC network protection.

**Enhanced/unconventional protection-systems:** There is always a plethora of papers aiming to improve the operation of conventional protective methods, either by utilising advanced processing techniques, or by taking advantage of emerging technological developments. This Special Issue is no exception. You will find some fine examples of unconventional thinking and innovation in most of the presented papers.

**Protection of superconducting transmission systems:** Due to the introduction of superconducting cables, long-distance superconducting electricity transmission has recently become a reality. Due to their unique physical characteristics, such cables require special attention when it comes to protection. We are pleased to present one paper which specifically addresses this new exciting area of research.

**Lightning protection:** Last but not least, we have one paper which addresses an important aspect of lightning protection in building integrated photovoltaic modules.

> **Adam Dy´sko, Dimitrios Tzelepis** *Editors*
