Deutsche Bahn

ESG provides design pack

for Virgin Train’s Class 91 Power Supply Units

(Derby, 21. November 2017) The traction electronics power supply units (PSUs) fitted to Class 91 locomotives operated by Virgin Trains East Coast (VTEC) were occasionally failing, this affected the service provided by VTEC and resulted in additional unplanned repair work at depots. Investigations into the existing original power supplies showed that they were over 20 years old and as a result the components were difficult to obtain, or were even obsolete.

ESG Rail undertook a peer review to detail the various options for this PSU problem, and due to the now obsolescent components, this review included the reverse engineering of the circuit board and its components. There then followed a component validation exercise, which successfully found and validated alternate components.

ESG Rail were then asked to provide a design pack to cover the new Electronics Power Supply Unit (EPSU) and the Gate Turn-Off Thyristor (GTO) so that an approved supplier could build and test the new design dc-dc convertor, the 26EVO21B1 PSUs.

As replacement/equivalent parts were being used, ESG Rail made sure that the design pack included the necessary direct replacement component certification.Following successful delivery of the above design, ESG Rail were asked to undertake a first in class EPSU trial overhaul, in conjunction with an accredited supplier. This trial proved successful and as a result the other thirty one vehicles were overhauled with the new replacement 26EUO21B1 PSU modules.

Work Undertaken


Successfully Delivered

  • ESG Rail produced mechanical assembly and electrical drawings on ROSCO drawing frames.
  • Produced the necessary modification documentation and associated assembly and test procedures.
  • Produced the design pack to enable an approved supplier to build and test the new design.
  • Acquired the necessary direct replacement component certification.
  • Carried out first in class overhaul and trial, see below.

Trial and Overhaul

  • In conjunction with an accredited supplier, ESG Rail carried out a first in class overhaul of a 26EUO21B1 PSU, including calibration and testing. This overhaul was trialled by VTEC.
  • As a result of the successful first in class trials, ESG Rail procured the replacement electrical EPSU components for the other thirty one VTEC Class 91 vehicles. This included the replacement 26EUO21B1 PSUs and manufacture of the associated printed circuit boards (PCBs).
  • The PCBs were populated with their components, the PSUs overhauled, calibrated and tested in accordance with the latest design documents.Note for editors:



For media enquiries contact Heidi Lee, Communications Manager, ESG Rail – 01332 483 849 (mobile - 07870 958043) or email:

About ESG Rail - ESG Rail is the route to market for DB’s technology expertise. As part of the DB Group, ESG provides innovative, value-led strategic advice, technical consultancy and technology integration. Based in Derby, home to the largest cluster of railway companies in the world, ESG is a leading rolling stock consultancy and provides services to many of the UK’s train operators, manufacturers, owners and maintainers.