**1. Introduction**

The electrical energy industry is undergoing dramatic changes; the massive deployment of renewables, an increasing share of DC networks at transmission and distribution levels, and at the same time, a continuing reduction in conventional synchronous generation, all contribute to a situation where a variety of technical and economic challenges emerge. As society's reliance on electrical power continues to increase as a result of international decarbonisation commitments, the need for the secure and uninterrupted delivery of electrical energy to all customers has never been greater.

One of the important areas, sometimes overlooked, is power system protection, which is a safety-critical component of all electrical systems. The fast and reliable detection of abnormal conditions, as well as the identification and prompt removal of faulty components, help in preserving system integrity and minimise the 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 10 interesting papers that cover a wide range of topics, all related to protection system problems and solutions.
