Transforming the face of UK power distribution



Transformers are perhaps one of the single most important aspects of a building’s services, acting as the key connection between the national grid and the premises’ internal power distribution network. For years, oil transformers have been the go-to choice for consultants and specifiers, yet advances in rival technologies are now putting credentials of the age-old favourite under the microscope.

Here Steve Marr, an expert in power distribution at Legrand UK, delves deeper into the debate given its 21st century setting.

Like so many other aspects of the electrical industry, the transformer debate is one full of nuances and historical bias. Oil transformers have long been the transformer of choice for many specifiers and consultants. The technology has been in use for over a hundred years and has formed a reliable power conduit for industrial and commercial projects across the world for decades. However, the rise in alternative transformer technologies, typified by the development of cast-resin transformers (CRTs) in the 1980s, sparked a debate into whether the days of the oil transformer are numbered.

Over 25 years on and the debate is still going, however the tide may be turning in favour of CRTs, with consultants and specifiers firmly focused on sustainability going forward with new projects. A transformer is expected to last the life of a building, and with most buildings generally lasting 20 years before they are refitted or repurposed, it would be very unusual for a transformer to be replaced during this time, bar a serious technical issue. However, it is the sustainability factor – taking into account a transformer’s emissions and its overall total life cost – which may give CRTs the edge of their older counterparts.

Despite their reliability over the years, oil transformers do present a number of issues – both during the installation stage and their subsequent operational life – which CRTs do not, all of which should certainly be factored in during the specification process for new transformers.

In oil transformers, the windings are inserted inside an enclosure filled with a liquid – generally mineral oil, which has the double function of guaranteeing adequate insulation between the windings and the earth, and dispersing the heat generated by the normal operation of the transformer itself. The oil increases in volume as the temperature of the surroundings of the transformer itself rises. To compensate for these variations of volume within the insulating liquid, some transformers have an “expansion vessel”, situated in the upper part. This tank communicates with the outside by means of filters to remove the humidity which, if it accumulated, could impair the dielectric properties of the oil, and consequently the transformer itself.

As such, there will be a sustained level of regular maintenance required throughout the operational life of an oil transformer. When coupled with the fact that, if poor maintenance practice is adopted and leaks occur, the transformer itself can pose a potential fire risk to personnel, and also risking huge downtime for the business or application due to power loss.

In a bid to negate potential fire risks, oil transformers are generally situated outside of a building. Whilst this may be beneficial for commercial properties in densely populated areas such as Central London, in reality it can have a knock-on effect on the overall system efficiency. In fact, on the surface there may seem little difference between oil transformers and CRTs as any new transformer of either type has to perform within the limits set for load and no-load losses as stipulated by the most recent (July 2015) changes to the EcoDesign Directive.

However, these figures are based solely on the transformer and are only comparable if they are situated in the same place. As already mentioned, most oil transformers are situated externally and as such, require a higher volume of cable or busbar trunking to distribute the power from the transformer into the internal electrical infrastructure. If you take into account the extra trunking or cabling required, and its associated volt drop and losses, the overall system efficiency of an oil transformer-based power distribution system will be noticeably worse than one which employs an internal CRT.

One further point to bear in mind, when looking to specify a transformer, is its end of life disposal. While some parts of a transformer can be recycled, oil from within a used transformer is classed as a hazardous waste and therefore must be disposed of as such and in line with the Waste Framework Directive. CRTs however – such as the high efficiency Zucchini range from Legrand – on the other hand, are more easily disposed of through normal waste channels and recycling methods.

Whilst there may be little separating an oil transformer and a CRT on a data sheet, it is when you consider their performance over their operational life that the differences come into focus. Requiring much more routine maintenance, as well as the power losses incurred due to the necessity to locate an oil transformer externally, in the long term a CRT will offer end users a much more favourable total life cost, as well as improved power efficiency.

Ultimately, as with so many modern advancements across the electrical industry, the biggest barrier to change is man. Oil transformers have been the go-to choice for consultants for decades, however I would urge anyone looking to specify a transformer to look at the wider options available. Just because something has worked well for the last 30 years doesn’t necessarily make it the right choice for the next 30. With energy efficiency fast becoming one of the long-term KPIs of a building, CRTs offer a valuable opportunity to make a power distribution system as efficient as possible.