With the development of DC power transmission and distribution technology, power equipment such as converter transformers, DC cables, and DC gas-insulated equipment has been widely used in the power grid. In addition, with the growing attention of hybrid and all-electric vehicles including electric aircraft and electric ship in commercial transportation and military industry, the stability of the propulsion system driven by DC voltage has become a great concern in recent years and will continue drawing much more attention in the near future.

At DC voltage, partial discharge (PD) may take place and pose a threat to not only the insulation but also the communication system. Although an in-depth understanding about PD behaviours at AC voltage has been reached, emerging issues relevant to DC PD are ambiguous mainly due to the effect of complex charge dynamics at DC voltage.

This Special Issue brings recent studies of PD at DC voltage, in which four high-quality research papers are finally selected and accepted for publication. The scope of these four papers covers PD measurement, PD characteristics and mechanism, and PD classification solutions, which are all hot issues that people are concerned about recently. A brief introduction of each paper is presented as follows.

随着直流输配电技术的发展，换流变压器、直流电缆、直流气体绝缘设备等电力设备在电网中得到广泛应用。此外，随着包括电动飞机、电动船在内的混合动力和全电动汽车在商业运输和军工领域的日益关注，直流电压驱动的推进系统的稳定性近年来已成为人们关注的焦点，并将继续受到关注。近期会受到更多关注。

在直流电压下，可能会发生局部放电 (PD)，不仅对绝缘而且对通信系统构成威胁。尽管已经对交流电压下的 PD 行为有了深入的了解，但与直流 PD 相关的新问题主要是由于直流电压下复杂电荷动力学的影响而模糊不清。

本期特刊带来了直流电压下局部放电的最新研究，最终选出并接受发表的四篇高质量研究论文。这四篇论文的范围涵盖了局部放电测量、局部放电特征与机理、局部放电分类解决方案，都是近期人们关注的热点问题。每篇论文的简要介绍如下。