Solid-State Circuit Breakers Are the Adjacent Technology to Solid-State Transformers and Face the Same On-State Loss Problem
- SSCB topologies: pure solid-state (IGCT/GTO/IGBT series), pure mechanical, hybrid (SSCB + ultra-fast mechanical switch)
- Pure SSCB: microsecond fault interruption, no arc, no mechanical wear; 15-30% on-state losses
- Hybrid breaker: fast SSCB response with lower steady-state losses through parallel mechanical path
- SiC MOSFET on-state resistance: ~50 mu03a9u00b7mmu00b2 (2018) u2192 <10 mu03a9u00b7mmu00b2 (2025) u2192 <5 mu03a9u00b7mmu00b2 target (2028)
- ABB, Eaton, Hitachi Energy each have both SST and SSCB product lines — co-evolving industries
Solid-state circuit breakers (SSCBs) are the closest adjacent technology to solid-state transformers in the power-electronics device hierarchy. Both use silicon carbide MOSFETs and silicon insulated-gate bipolar transistors (IGBTs) as the primary switching device. Both replace electromechanical equipment (the conventional iron-core transformer in the SST case, the electromechanical contactor or molded-case circuit breaker in the SSCB case) with semiconductor alternatives. Both face the same fundamental on-state loss problem that limits how aggressively each technology can replace the legacy equipment it competes against.
The SSCB family includes three topologies. Pure solid-state circuit breakers use semiconductor switches (typically integrated gate-commutated thyristors, gate-turn-off thyristors, or IGBTs in series) and can interrupt fault current in microseconds with no arc, no mechanical wear, no acoustic signature, and no magnetic flicker. Pure mechanical circuit breakers retain the conventional design and respond in tens of milliseconds with arc-extinguishing chambers. Hybrid circuit breakers combine a fast solid-state element in parallel with an ultra-fast mechanical switch, achieving the response time of the solid-state element at much lower steady-state losses than a pure SSCB.
The economic case for SSCB adoption depends on the application. In high-cycling applications (industrial process loads, microgrid intentional islanding, EV fast-charging interconnects), the long service life and zero-maintenance characteristics of the SSCB justify the cost premium. In low-cycling applications (utility distribution feeder protection that operates a few times per year), the on-state losses of the pure SSCB and the higher unit cost relative to molded-case alternatives make the SSCB economically marginal.
The 15-to-30 percent on-state loss penalty cited in the SSCB literature is the same problem the SST industry has had to solve through device-level efficiency improvement. The progression of SiC MOSFET on-state resistance from approximately 50 milliohm-millimeter-squared in 2018 to under 10 milliohm-millimeter-squared in 2025 has been the enabling improvement for both SST and SSCB commercialization. Future SiC device generations targeting under 5 milliohm-millimeter-squared by 2028 will further compress the on-state-loss penalty for both technology families.
The strategic implication is that the SST and SSCB industries are co-evolving and largely co-located. Companies investing in SST capacity also tend to be the same companies investing in SSCB technology. ABB, Eaton, and Hitachi Energy each have product lines in both. The startups in the SST industry are watching the SSCB market carefully because the same SiC supply-chain constraints that limit SST production also limit SSCB production, and the integrated systems that emerge (an SST with built-in SSCB protection) are likely to be the dominant product form factor by 2028 and beyond.
Why It Matters
For power-electronics buyers, solid-state circuit breakers share the SST’s SiC device base and the same on-state loss problem that limits how aggressively either can displace legacy equipment, so progress on one informs the other. A $5 billion SSCB market forecast means device makers are amortizing SiC and thermal-management R&D across two product lines at once, which can pull SST component costs down faster than SST volume alone would.
Critical Perspective
Editorial correction: This post is part of MGRID’s Solid-State Transformer industry coverage. As of May 2026, that body of work systematically framed manufacturer announcements, funding rounds, and laboratory demonstrations as commercial deployments. The reality is that field-deployed commercial-class SST in revenue service globally is measured in single digits, and almost every product cited in this series is at “announced” or “funded” stage, not “operational.” Readers should treat the specific claims in this post against the standards documented in our SST Industry Reality Check (the per-claim audit table maps marketing language to verifiable deployment status). The corrective article is the canonical reference for SST industry reality; this post remains published with its original framing so the editorial drift is traceable.
Related Coverage
ABB, Eaton, Hitachi Energy each have both SST and SSCB product lines — co-evolving industries
