Jubilee Line Transformer Overhaul | Nieke, REO & R Baker

Halfway Through the Jubilee Line Transformer Overhaul Programme

R Baker (Electrical) Ltd has reached an important stage in our ongoing London Underground Jubilee Line transformer overhaul programme.

Following the award of the contract in December 2024, work began at our Liverpool facility in March 2025. With the programme scheduled to continue into late 2026, we are now well into the project, providing specialist electrical engineering support for equipment used on the Jubilee Line 1996 Tube Stock.

When we originally announced the contract, we focused on the scale of the project and what it meant for R Baker. Now that the programme is well established, we can take a closer look at the engineering behind these specialist railway transformers, their history, and the challenge of keeping legacy electrical equipment operating reliably after decades of service.

The project also has an interesting engineering heritage, connecting today’s overhaul work with Nieke Elektroapparate GmbH and REO AG (REO Train Power Magnetics) — names with a long history in specialist railway electrical equipment.

Supporting the Jubilee Line 1996 Tube Stock

The 1996 Tube Stock has been operating passenger services on the Jubilee Line since the late 1990s.

Over that time, the fleet has accumulated millions of miles in one of the world’s most demanding urban railway environments.

Keeping established rolling stock in service requires considerably more than routine maintenance. As equipment ages, operators must address challenges including component obsolescence, insulation ageing, mechanical wear and the declining availability of original components.

This is particularly important for specialist electrical equipment.

Unlike many modern electronic components, a railway transformer installed decades ago cannot necessarily be replaced with an off-the-shelf equivalent.

Its electrical characteristics, physical dimensions, insulation system, cooling, connections and interaction with other onboard electrical equipment all have to be considered.

What Is a Converter Output Transformer (ASIT)?

TfL’s own historical procurement records have identified R Baker (Electrical) Ltd in connection with equipment described as a Converter Output Transformer (ASIT).

These specialist transformers form part of the train’s auxiliary electrical power system.

While traction equipment provides the power required to move a train, a London Underground train also requires electrical power for numerous auxiliary systems.

Transformers associated with these systems therefore have an important role to perform while operating in an exceptionally challenging environment.

Railway electrical equipment must withstand vibration, repeated heating and cooling cycles, contamination and long operating hours. Equipment associated with power electronic converters must also be designed around the electrical characteristics of those systems.

Over decades of operation, those demands can take their toll.

The 51kVA Jubilee Line Transformer

The transformer equipment associated with the current engineering programme is rated at 51kVA and forms part of the auxiliary electrical architecture of the Jubilee Line fleet.

A transformer’s kVA rating, however, tells only part of the story. For legacy railway applications, engineers also need to consider factors including winding configuration, voltage ratios, insulation, thermal performance, mechanical construction, mounting arrangements and the characteristics of the electrical equipment surrounding the transformer.

This is one reason maintaining obsolete railway transformers requires specialist knowledge.

Simply finding another 51kVA transformer does not make it an equivalent component.

The original equipment was engineered for a specific application, and preserving the appropriate electrical and mechanical characteristics is critical when undertaking overhaul work.

Nieke Elektroapparate GmbH: A Railway Engineering Legacy

An interesting part of the history surrounding this generation of railway electrical equipment is Nieke Elektroapparate GmbH.

Based in Hennigsdorf, Germany, Nieke developed expertise in specialist electrical and magnetic components for railway applications.

Although the Nieke name is less familiar today, its engineering legacy remains relevant wherever older railway equipment continues to operate.

In 2004, Nieke Elektroapparate GmbH was acquired by REO.

This is particularly significant for the rail industry because fleets frequently remain in operation for several decades. By the time a transformer, choke or other magnetic component requires major attention, the company that originally designed the equipment may have changed ownership, stopped manufacturing the product or disappeared altogether.

Preserving engineering knowledge therefore becomes an important part of managing railway obsolescence.

From Nieke to REO AG and REO Train Power Magnetics

Today, REO AG and REO Train Power Magnetics continue to specialise in electrical components for railway applications.

REO’s railway portfolio includes products such as transformers, chokes, current transformers and resistors, while its Hennigsdorf operation maintains an important connection with the railway engineering expertise associated with Nieke.

REO has itself highlighted the significance of the Nieke acquisition for supporting legacy railway products, including equipment manufactured many decades ago.

That continuity demonstrates something R Baker encounters regularly in the rail sector: the working life of railway equipment can considerably exceed the commercial life of the companies, materials and manufacturing processes originally used to produce it.

For organisations maintaining established rolling stock, access to both original engineering knowledge and specialist overhaul capability can therefore become increasingly important as fleets age.

Halfway Through – and Continuing

Reaching this stage of the Jubilee Line transformer overhaul programme is an important milestone for everyone involved at R Baker.

What began with a contract award has become an established production programme, with specialist transformer assemblies progressing through our Liverpool facility week after week.

And there is still plenty of work ahead.

As the programme continues through 2026, our focus remains the same: applying our electrical engineering, winding and transformer expertise to support the overhaul of these important railway assets.

For us, the project is also a reminder that good engineering rarely ends when a product leaves the factory.

Sometimes the real engineering challenge begins decades later — when equipment has become obsolete, supply chains have changed, and the railway still depends on it every day.

We are proud to be applying R Baker’s specialist transformer expertise to help support the continued operation of London’s Jubilee Line.