Transformer transformations

A transformer is a device that transfers electrical energy from one circuit to another through a shared magnetic field. A key application is to ‘tap off’ 11 000 volts (11 kV) of electrical power from the national grid and step it down to 415 volts, the normal three-phase electrical power system used in the UK for commercial, institutional or industrial applications.

A transformer therefore makes raw electricity ‘usable’, as well as allowing it to travel through cables. In fact, most of the world’s electrical power has passed through transformers by the time it reaches the user.

Large, high-power transformers, in particular, need to have a built-in cooling facility to transport heat from the interior. Thus one of the numerous ways of classifying transformers is according to cooling type. For example, for power transformers rated up to a nominal kVA, natural convective air-cooling, often fan-assisted, is adequate.

Traditionally, oil transformers have relied on highly refined mineral oil as a cooling medium, while in the latest generation of cast-resin transformers, the core is insulated by a thin coating of inorganic material.

Fire safety

Over the past decade the remarkable advances in materials technology and manufacturing methods have fostered the popularity of cast-resin transformers, particularly in fire-sensitive locations such as high-rise structures, hospitals and public buildings, where the transformer is located indoors and a fire outbreak would be particularly hazardous because of the high density of people.

Safety is high on the list of benefits of cast-resin transformers. The advanced epoxy mixture used in such transformers is a non-hazardous material, which is both fire-resistant anself-extinguishing. Even when the material is exposed to arcing, no toxic gases are produced, and the transformer can safely be situated close to the load, saving on cabling, civil works and transmission loss.

Another key benefit is the fact that cast-resin transformers require little or no maintenance during their lifetime.

Compare these benefits with the disadvantages of traditional oil transformers, with their relatively low fire point, pollution potential, higher installation costs (due in part to the fire-protection and containment measures often needed) and high maintenance requirement.

Oil-cooled transformers are not a favourite with insurance companies.

Oil is a non-renewable resource, while cast-resin transformers are insulated in a sustainable material, which has been developed and refined over 15 years to comply with European Union and national directives on the protection of the environment.

They do not pollute the environment and are recommended for all companies that subscribe to ISO 14000, a standard that helps organisations minimise the negative effects of their operations on the environment.

Aggressive conditions

As well as protecting the environment, the high-quality epoxy resin is filled with silica and trihydrate alumina, that has been developed to encapsulate transformers and stop moisture ingress.

This prevents electrical breakdown under load, as well as inward pollution from the environment. This not only makes the transformers suitable for damp or dirty conditions but extends the life of the transformer’s working parts and reduces maintenance.

Some manufacturers’ transformers are also coated in high-vacuum chambers to reduce air or other gases in the resin, which could produce partial earth discharges. In effect, they thermetically seal the transformer’s core.

Another point is that cast-resin transformers do not have the noise and vibration problems associated with oil-based machines.

Cast-resin transformers are now available in different specifications to meet the needs for hazardous or unforgiving environments, exceptionally cold ambient temperatures and environments with a high fire risk.

One of the most gratifying outcomes of installing environmentally friendly technology in recent years has been the realisation by individuals and companies that saving the environment can also save money. As well as being favourably priced, cast-resin transformers are exceptionally energy-efficient, producing a high transformation yield and thus consuming less input energy.

Zucchini EdM has developed a mathematical model that highlights the savings that can be made by the user of a given electrical item on a case-by-case basis. For example, a 1000 kVA energy-efficient transformer produces savings of €30 000 over a 20-year period, the equivalent of 20 MWh per year.

The European Commission has assessed that if equipment such as this were brought into general use, emissions of 11 million tonnes of carbon dioxide equivalent to the electrical power used by five million homes would be avoided.

David Taylor is contracts manager with Zucchini EdM Transformers