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DITA – The Game Changer

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Be careful of what you wish for, as you may just get it.” It’s one of those quotations that are often used but no one really knows where they come from. An online search finds attributions to an old Chinese curse (May you live in interesting times, may you find what you are looking for, and may you come to attention to those in authority), Saint Teresa of Avila from the 16th century (There are more tears shed over answered prayers than over unanswered prayers) and even the ancient-Greek author Aesop (We would often be sorry if our wishes were gratified).

However, in the case of distribution interface transformer assemblies (DITA), they answer all the questions, solve many of the challenges and deliver a whole range of benefits that align to providing interface, management and resilience in signalling power supplies.


In recent years, Network Rail’s Class II product and system standards have helped to deliver a new generation of signalling power supply products. This system removes the continuous earth wire, instead earthing equipment locally, so signalling power supply runs now have only two cores, reducing the use of copper by a third.

Alongside this has been a revolution in transformer technology. The use of aluminium windings, the development of low-inrush and high-efficiency designs, improvements in reliability and the user interface have all resulted in a significant range of Class II and hybrid transformers.

Now, using proven Class II switchgear that was developed to deliver Network Rail’s new signalling projects and provide upgrades to existing legacy systems, the DITA builds on that success in terms of safety, system reliability and user interface.

This range is an unprecedented new generation of full Class II power transformers that exceed the minimum requirements of Network Rail specifications with ground-breaking benefits, utilising on board eco-rail® technology that is fast becoming the preferred solution on the railways.

The DITA range of transformers is a pioneering technology that delivers the lightest, most compact and environmentally friendly solution available. It has been developed with Network Rail and deployed to support key strategic improvement schemes such as copper elimination, inrush reduction and the reduction of carbon emissions throughout the network.

Key features

The new range of Class II DITA transformers now offers the following benefits:

  • Seamless integration and tested/proven thermal rise compatibility with Network Rail standard apparatus housings and associated equipment;
  • The ability to reset or boost various distribution voltages;
  • Galvanic isolation and capacitance decoupling of feeder circuits;
  • The facilitation of Class I legacy to Class II feeder integration aligned to NR/L2/SIGELP/27419;
  • A full Class II designation prevents the need for expensive earthing surveys and bonding where adopted;
  • Inrush characteristics across the whole range of less than five-times full load system current;
  • A stable of power ratings from 5 to 40KVA with single and dual output multi-voltage configurations to cover all regional distribution voltages;
  • Lightweight aluminium windings and connection technology eradicate the use of expensive and fast-exhausting copper reserves to support sustainability;
  • Unmatched efficiency delivering enhanced asset life in excess of 400,000 hours continuous operation.

Waiting in the wings, the supporting act is a range of insulation monitoring and fault location technology that will support the DITA intelligence and allow it to become a strategic management tool in the network of low-voltage signalling power feeders.

The boost capability within the Tx tappings allows for multiple benefits when looking to support long feeder distances as well as offering cable reduction possibilities.

All this technology needs some careful packaging and the newly approved GRP (glass-fibre reinforced plastic) apparatus case does just that – the twin-skin material allows for significant thermal movement while managing solar gain and temperature spikes. The case construction is tested to over 50kV insulation resistance and therefore provides a very safe environment for the 650V. Mitigating against earth bonding the case, this allows for only a moderate earth value to support the IMD (insulation monitoring device) in Class II applications.


Network Rail has issued DITA Standard NR/L2/SIGELP 27419 with a view to providing an easy step-by-step guide to identifying, prescribing and implementing DITA in a wide range of feeder scenarios. The standard has allowed designers to understand and then support the specification of DITA on projects as well as giving a benchmark to the supply chain.

Other supporting Network Rail documents, including “System Architecture Mix and Match Rules” and “Class II Retrofit Design Philosophy”, help to explain the DITA unique selling propositions. A recent standard, NR/L2 /SIGELP 27416 – Modification of Legacy Power Supplies – helps to complete the supporting Network Rail documents, providing an outline and some examples of where DITA can be used to great effect.

Finally, TECM (Target Earth Calculation Model) allows designers to establish target values and feeder sub-division lengths, helping to establish the key locations where DITA will support the network.

Supply chain engagement

Riding on the massive success of Class II over recent years, the DITA is a further opportunity to expand the product range and integration possibilities.

As no single supplier can offer the entire product, collaboration is the key to the success of taking DITA to the market place. As a product that may be considered new and novel, the DITA requires some robust support from the supply chain to aid design and specification, to demonstrate a wide range of features and benefits, to understand fully and align with the examples set out by Network Rail and finally to offer the optimum product for the application.

The opportunity that DITA offers to Network Rail’s current infrastructure is substantial; the key to unlocking that potential is early engagement and a real in-depth understanding of the whole system benefits. The wide range of suppliers and collaborators will ensure the success of this innovation, as projects take up the DITA and realise its true potential to deliver the solutions to many unanswered questions.

Challenges and payback

The current Network Rail low-voltage network is dominated with Class I IT systems, many of which have long feeders with significant numbers of FSPs (functional supply points) on each feeder. All the usual infrastructure challenges exist including, challenging earthing conditions, cable theft and damage, rodent attack and demanding maintenance conditions.

One goal would be to have a more manageable network, smaller feeders, better fault location, advanced programmable protection systems and controllable interfaces between system architecture. If all of the above sounds like a challenge you may be facing, then look at the DITA.

As with all new assets, there has to be a cost driver. For the DITA, this can come in many guises. Providing a definitive and controlled demarcation between Class I and Class II can be a costly business if it requires the removal and replacement of large amounts of existing infrastructure. The DITA will allow this interface to happen when needed and the twin output options allow for feeder optimisation, leaving the system designer in control of cable sizes according to load.

Dividing up the network into smaller portions will have a significant benefit in fault location, maintenance and re-establishing the operational railway.

The DITA offers new signalling projects the opportunity to have a legacy interface without any costly replacement of existing assets as the legacy interface can be selected based on the optimum start and finish rather than a widespread or complete feeder renewal.

Adopting a DITA switchgear assembly allows for the integration of new Class II twin-core and four-core FGT (fibre glass tape) cable as well as offering a Class I interface for three-core and armoured legacy systems. The large termination enclosures have been designed in line with BS BS5372:1997 and to facilitate the use of aluminium cable and the PADS-approved bi-metallic pins or lugs. This supports Network Rail’s Copper Elimination Challenge, thereby further reducing material costs. Cable sizes up to 150mm twin-core and four-core aluminium and copper cable can be accommodated.

A unique set of circumstances is opening up on the existing rail network. Necessity is driving change, challenges are outlined in Network Rail innovation targets and supported by a range of new ‘SIGELP’ standards, products like DITA are an outcome of one of these challenges.

In delivering solutions to this challenge, the supply chain has a significant part to play in delivering the technology improvements, cost savings and collaboration that is critical to meeting CP6 targets.

Riding on the success of Class II, products such as DITA make up a basket of products to deliver a more-resilient signalling power backbone to satisfy the growing demand on the network.

Peter Dickson is engineering manager at iLecsys.

Read more: Infrarail 2018 – ready to ExCeL!


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