A crucial link relieved from pressure

HVDC transformer follow up order from UK. The bi-directional cross channel link between the United Kingdom and France is considered by many as the most important energy link between the two nations. Not only does the link play a considerable role in France, but it also provides three million homes with electricity in England alone.

A critical link

The cross channel link between the United Kingdom and France is, heavily relied upon by both countries to provide a safe and reliable energy supply. Any fault or interruption could spell a major disruption.


Hence, when just that happened at the Sellindge substation in 2016, the National Grid entrusted Siemens to find a solution. The grid operator requested a repair of the faulty unit to restore standard operation in minimum down time. Alongside this, they requested a new HVDC unit, which could fit perfectly into the old space.


Now again, National Grid ordered another four new 315MVA, 400kV AC, 117kV DC power transformers to further enhance its Sellindge substation and guarantee an uninterrupted power exchange between the United Kingdom and France. National Grid asked for minimal effects in installation, and time conscious manufacturing and delivery of the units.

Complex requirements

The Sellindge substation is not only immensely prone to errors due to its age, but also the company which built the original transformer no longer exists. Moreover the original drawings were partly unreadable or unavailable.


“The substation is almost 40 years old,” explains HVDC Transformer Sales Manager Igor Mladenovic from Siemens. ”The entire set of parameters needed to be newly recorded and of course the electrical and mechanical parameters for the new units needed to fit exactly.”


The connections to the valve hall, the wall openings for the cooling systems, everything had to be adapted and redesigned to the inch. As well as this, official on-site regulations for the noise emission are very strict, thus this also applies to the HVDC transformer.


Siemens Transformers has bundled all its skills and know-how in order to satisfy the customer’s needs – incorporated in an innovative electrical- as well as in a mechanical transformer design. This was also reflected in transformer efficiency, which means the transformers were developed with minimal losses. Finally, fire protection also played a big role for the client. He wanted an integrated fire deluge system on the transformer.

The results

Siemens will provide a customized system in strong cooperation with the renowned fire deluge system sub-supplier. The fire deluge system was crucial for the customer’s flexibility for the case when he moves the spare transformer from the storage position in to the service position.


The National Grid will receive four newly designed units that fulfill multiple additional requirements. They are quieter than their predecessors, more powerful and also cheaper to operate. “We have suggested many possibilities to the customer and conducted many mutual workshops. We have looked at which criterion are most important on the long run and also considered the maintenance possibilities. The result is in the end the most economic and powerful solution in the long term,” says Mladenovic.


High capacity, simultaneously minimal losses and absolutely reliable availability of the transformers were crucial for this strategically important substation, and led to the choice of the leading supplier of innovative transformers, Siemens. By the end of 2018 and early in 2019 the four new transformers will be shipped to Great Britain. The transformer that the customer ordered last year is ready and now in the final stage of preparation to be sent to the substation.