ABB’s 2011 PETT on Swiss Federal Railways Was the First Solid-State Transformer in Revenue Rail Service

ABB launched its Power-Electronic Traction Transformer (PETT) prototype on a Swiss Federal Railways (SBB) Ee 933 shunting locomotive in mid-2011, certified by the Swiss Federal Office for Transport at the end of that year. The PETT was the first solid-state transformer (SST) installed in a revenue-service rail application anywhere in the world. The pilot is the canonical reference event for traction-SST commercialization and is the foundation under most of the medium-voltage SST product development that followed.

The engineering case for the PETT was specific to European rail electrification. The Swiss network operates at 15 kilovolts AC at 16.7 hertz, a legacy frequency dating to the limits of mechanical synchronous-converter technology in the early twentieth century. A conventional iron-core traction transformer at 16.7 hertz must be physically large and heavy to handle the magnetic flux at that low frequency. On a locomotive or multiple-unit train, every kilogram of transformer mass directly displaces passenger capacity or freight capacity, and contributes to braking energy loss.

The PETT replaced the conventional 16.7-hertz iron-core transformer with a three-stage power-electronics converter using high-frequency intermediate magnetics. The reported weight reduction was significant — roughly half the mass of the equivalent iron-core unit for the same kVA rating. The PETT also enabled active power-quality features that the conventional transformer could not provide: regenerative braking energy recovery to the catenary at controlled power factor, harmonic suppression on the catenary side, and onboard auxiliary-power conditioning.

The pilot SBB installation ran in revenue service for several years and provided field reliability data for ABB’s subsequent product development. The PETT name has continued to appear in ABB and Hitachi Energy product literature as the heritage architecture from which today’s medium-voltage SST products are derived. Other rail-equipment suppliers including Alstom (which has since acquired Bombardier’s rail business), Stadler Rail, and CRRC of China have developed their own traction-SST architectures with parallel goals.

The PETT pilot also matters because it was the first commercial-class SST to validate the field-reliability assumptions that critics of the architecture had been raising since 1968. The conventional iron-core transformer’s reliability over decades is the benchmark every SST architecture has had to clear. The PETT’s service track record contributed materially to the confidence that today’s commercial SST suppliers (ABB, Hitachi Energy, Eaton, DG Matrix, Amperesand, Heron Power) can sell against utility and data-center procurement requirements.

Why It Matters

For the traction and rail market, ABB’s 2011 PETT on Swiss Federal Railways is the proof point every later medium-voltage SST product traces back to, because it ran in revenue service rather than a demonstration. Fifteen years of rail operating data is exactly the reliability evidence that grid-side buyers lack, which is why the rail precedent keeps getting cited in utility SST business cases.

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](/?p=9044) (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

• The 1968 GE Patent That Founded Solid-State Transformer Technology: traces the origins of solid-state transformer technology
• FREEDM Systems Center at NCSU: The 2008 NSF Center That Turned Solid-State Transformers Into Real Devices: details early research into solid-state transformers
• Eaton Closes Acquisition of Resilient Power Systems to Bring Medium-Voltage Solid-State Transformers In-House: Eaton acquires medium-voltage solid-state transformer capabilities
• Why the Iron-Core Transformer Has Outlasted Every Replacement for 130 Years (And What Finally Threatens It): discusses the obsolescence of iron-core transformers