A marked transformation


Although the role a transformer plays in electrical circuits is something that is never likely to change, these specialised products certainly are. Steve Marr, marketing manager for Legrand’s power distribution division, talks to Electrical Review about the rise to prominence of cast resin transformers


As with any technically driven market, the electrical manufacturing industry is awash with tried, trusted and often much-loved products that have been put under extreme threat, and in some cases, usurped by the new kid on the block.

Cables and busbar trunking are currently locked in a gripping tussle for installation dominance; plastic distribution trunking briefly challenged the dominance of the long established metal market leader; and, of course, the fight continues between traditional cable tray and the steel wire version.

Interestingly, many of these disputes still rage on, with supporters of the different sides continuing to weigh in with their theories as to why one solution is superior to the other. But when it comes to transformers, the argument made for traditional oil products over modern cast resin models seems like a forlorn one, where there can be only one possible winner.

First and foremost, it needs to be taken into account that the constructional characteristics of cast resin transformers (CRTs) mean they can be considered for virtually any installation. And on top of that, they score highly in terms of their environmental impact, ease of installation and flexibility of use.

Environmental impact
Because CRTs are constructed using high-quality epoxy resin, they conform to the relevant international standards (IEC 60076-11: 2004) and have a significantly lower environmental impact than oil transformers. The epoxy resin also has the added advantage of being flame retardant and self-extinguishing, meaning cast resin transformers deliver reduced inflammablity, and minimum emission of toxic gases and opaque smokes (F1 fire resistance classification). They can also operate in damp, dusty, saline or polluted environments (E2 environmental test classification) and offer high resistance to thermal shocks (C2 climatic test classification).

Furthermore, because they have no need for cooling fluids, they don’t present a pollution risk.

And if that wasn’t enough, CRTs can be considered as having the construction that most respects the environment. This is particularly important when the machine comes to the end of its working life and needs to be disposed of. The resin itself is considered an inert material and so can be sent to landfill, while the primary and secondary windings are easily recycled.

CRTs are, on average, 16% smaller in dimension and 10% lighter in weight and as such are easier to handle. Additionally, they do not need the same kind of expensive building work that is associated with the installation of traditional oil transformers – i.e. collection pits, extinguishing grids and fire-resistant separation barriers to prevent the propagation of fire and the spreading of insulating liquids.

Thanks to the removal of expensive building works, and the greater safety levels and absence of cooling fluids, CRTs also have the benefit of being able to be installed inside buildings, even near to rooms where people are present. The advantage of which is the closer to the load the transformer, the greater the saving in terms of connection cost, plus the additional benefits of a reduction in supply line downtime.

As CRTs use air cooling they take longer to reach operation temperature, which means they can be more overloaded than insulating liquid transformers and so are particularly suitable for supplying loads with frequent current breakaway starting current. Care does though need to be taken, as the temperature rise on the windings cannot remain above the allowable value for long periods of time.

The feed unit can also be temporarily increased by means of the application of forced ventilation systems – a process that is used to tackle particular operating situations, such as temporary overloads, high room temperatures or to make available a temporary reserve of power when, for example, there is an emergency caused by the transformer being out of service.

A question of cost
The odds are clearly stacked in favour of CRTs in terms of performance, but how do they rate when it comes to what, for many is still seen as the key specification driver, namely cost?
Analysing cost isn’t as simple as looking at the comparative purchase prices of the different transformers. What needs to be done to ascertain the most economical solution is to run a comparison that covers costs in terms of installation, operation, maintenance, disposal and, of course, purchase.

To correctly calculate a transformer’s operating costs, the no-load losses and the load losses need to be considered. The former is independent of the load and is constant for the whole time the transformer is connected to the mains. In contrast, load losses are incurred under load and are proportional to the square of the current passing through the transformer.
Enhanced materials can also be used that reduce the natural consumption of the transformers, while lower losses can be achieved through the use of higher grade magnetic steel in the core and/or a more efficient design of the winding. These efficiencies inevitably incur cost, and designers need to weigh up the efficiency benefits over the lifetime of a product against the initial outlay.

In regards to maintenance, CRTs cost significantly less. This is down to the fact that although they require regular checks, it is simply to ensure there is no accumulation of dust and dirt. In contrast, oil transformers have to be continually monitored to ensure the level of insulating liquid is correct and that its dielectric properties have not changed – something that can be affected by even the smallest traces of humidity.

Unfortunately, initial purchase cost is still seen by many as the key factor in the decision making process, and looked at purely from this perspective, oil transformers are cheaper. In fact, you don’t need to look too far back to find a time when CRTs were around 25% more expensive, but with oil prices rising, the cost of aluminium dropping, and the gap between the two quickly eroding, even this argument in favour of oil transformers is beginning to lose its impact.

Of course, in order to evaluate the true cost of a transformer, it’s the lifetime cost that needs to be considered rather than the purchase price. And CRTs offer the significant advantage of operating with lower losses, which in its simplest form means they consume less electricity. This delivers the benefit of lower carbon emissions and saves money, both of which are vital considerations at a time when reducing energy consumption is a key priority for all businesses.

Such is the level of confidence in CRTs, the lifetime cost argument now sees different types pitched against one another due to the fact oil transformers simply can’t compete.

Take for example a low loss CRT (transformer A) and a traditional CRT (transformer B). Both have the same power rating of 1000kVA, the same technical life of 20 years and the same losses at rated load of 9.8kW. The main difference though occurs in no-load losses, where transformer A records just 1.8kW and transformer B 3.1kW.

The result is that within just two years transformer A, despite costing significantly more than transformer B, has worked out far cheaper. And by the end of the 20 year lifetime of transformer A this saving has increased to virtually EUR30,000 (£25,000) – a sum that truly astonishes every electrical contractor and specifier we reveal it to.

Traditions in the electrical industry are, as we know, hard things to change and so the oil transformer isn’t simply accepting defeat with good grace and heading for the exit door. Instead, it is fighting back and it’s fighting back with the help of Midel – the synthetic oil with an impeccable fire safety record. Today Midel transformers are at least countering some of the arguments made in favour of CRTs and breathing new life into an argument that seemed to be heading for a unanimous outcome.