Abstract
Proposed to be the critical enabling component for future distribution networks, solid-state transformers (SSTs) have drawn much attention lately. They have a massive potential to help reduce size and weight, improve efficiency, integrate microgrids, renewables and energy storages in distribution systems, and can fulfil multiple grid functions such as bidirectional power flow control, fault isolation, system reconfiguration, and post-fault restoration. The introduction of these power electronics devices in distribution systems, however, also brings new challenges to the grid. Extra levels of electromagnetic interference, stray current, and personnel safety are among the most prominent practical issues that proper grounding arrangements can address. In this paper, considerations that should be factored into the grounding scheme design for SST ports with different voltage forms and levels are thoroughly reviewed and summarised. The characteristics of various grounding schemes used in AC and DC distribution systems are evaluated and compared in detail from different perspectives. Based on the comprehensive review, several combinations of grounding schemes are recommended for typical SSTs. In addition, the inclusion of new relay protection devices in the SST grounding scheme design, considering their characteristics and unique requirements, to enhance protection and reliability is also discussed.
Highlights
Conventional line-frequency transformers (LFTs) are widely used in distribution systems at different voltage levels
These grounding schemes are associated with different characteristics in terms of requirement of the basic insulation level (BIL), transient overvoltage (TOV) level under SLG fault, service continuity under SLG fault, personnel safety, thermal stress, electromagnetic interference (EMI) level, and relay protection sensitivity and coordination [49, 55,56,57]
This paper presents a comprehensive overview of grounding scheme design for solid-state transformers (SSTs)-enabled future distribution networks
Summary
Conventional line-frequency transformers (LFTs) are widely used in distribution systems at different voltage levels. Various power electronics-based devices [1], e.g. soft open points [2], hybrid transformers [3], and loop balance controller [4, 5], were proposed to act as critical nodes in future distribution systems to interlink grid segments with the same or different voltage levels. ∙ Structure and configuration of the connected grids; ∙ Grounding and protection schemes used in adjacent distribution systems; ∙ Voltage types and levels of the SST ports; ∙ Converter topologies of the SSTs; ∙ The mutual influence between different SST ports, including fault propagation and common-mode interference; ∙ Post-fault reconfiguration and restoration of the connected grids; and, ∙ Selection and coordination of the corresponding protection device. By including the related references and discussing the key points in a proposed framework, it intends to reveal the challenges and the possible future directions of this subject matter and serves as a comprehensive reference for researchers and practicing engineers in this field
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