A transformer performance has a major impact on electricity consumption, and operations and maintenance expenses of utilities, given the constant operation of the equipment over its 25-year service life, making it all the more essential to invest in energy-efficient transformers. The commercial viability of energy efficient transformers, coupled with low market penetration of highly efficient transformers, means that there is significant room for growth.
Transformers are static devices in electricity systems that transfer electrical power between circuits through electromagnetic induction. Their application enables significant energy savings by increasing the voltage and decreasing the current since losses are proportional to the amount of current flowing through the wire. Generally, electricity will pass through four or five transformers as it travels from the power plant to the customer.
Transformers have an average efficiency of around 98.5 per cent, making them some of the most energy efficient equipment. However, given their long service life, it is better to invest in highly efficient transformers to avoid accumulation of substantial energy loss in aggregate. Furthermore, sudden failures are reduced due to use of better grade materials and optimum design, in addition to lower cost of maintenance. These benefits add up and balance against the inevitable increase in purchase cost as additional copper in windings and better materials in the core will be used in the manufacture of high efficiency transformers.
The most common transformers are the liquid-filled transformer with windings that are insulated and cooled with a liquid. These transformers are most often used by electric utilities and can be found in all stages of the electricity network, from generation step-up through transmission and distribution. They are usually filled with mineral oil, which is flammable and may be prohibited for use inside buildings, but fire-resistant liquids are available. For instance, transformers filled with ester oil are also being promoted in crowded areas/cities to minimise accidents due to fire.
Another type of transformer is the dry-type transformer, which is insulated and cooled by air circulating through coils. These transformers are found in certain distribution networks and are typically used by commercial and industrial customers, rather than electric utilities. Liquid-filled transformers tend to be more efficient than dry-type transformers for the same rated power (kVA). They also tend to have greater overload capability and longer service life.
Types of losses
No-load losses: This includes both hysteresis loss and eddy current loss. The core flux in a transformer is practically constant for all loads – about 1-3 per cent variation from no-load to full-load conditions. Due to this the core loss is assumed practically constant for a given transformer.
Load loss: Also called as copper loss or short-circuit loss, this loss is due to resistive losses in windings/leads and stray losses that are due to flow of eddy currents in the structural steel work and windings. This loss is proportional to the square of current.
Cooling fan loss: This is caused by the power consumed by fans that cool the radiator bank/body of the transformer. The higher the transformer losses, the larger will be the size of the fan. This will result in increased losses in the cooling units.
The Bureau of Indian Standards bought out the revised standard IS 1180:2014, “Outdoor Type Oil Immersed Distribution Transformers up to and including 2,500 kVA, 33 kV – Specification Part 1 Mineral Oil Immersed”. This standard extends the scope of coverage beyond 200 kVA and up to and including 2,500 kVA and 33 kV. The use of low-loss cold-rolled grain oriented material or new technology such as amorphous distribution transformers are being used in emerging versions of transformers in order to minimise energy loss.
In recently installed transformers, various equipment such as moulded case circuit breaker, internal circuit breaker, and theft-proof LT enclosures are being integrated and embedded so that occurrence of transformer failure from overload is minimised. On account of a steep rise in the prices of copper and the problem of theft in remote areas, the manufacturing of distribution transformers is gradually shifting towards aluminium through the use of new technologies such as foil winding. The manufacturing of inverter duty transformers for solar application is also gaining ground due to an increase in the production of renewable energy.
Utilities are now focusing more on post-despatch inspections and third-party testing of selected samples to ensure proper checking of the material supplied so that the targets of energy efficiency are well achieved. Many other innovations such as sensors and smart meters with remote control facility are on the verge of being deployed widely. These sensors can help prevent failure, overloading, theft of electricity, etc., in both new and old transformers.
It would be extremely useful to develop an integrated policy fundamentals guide to ensure phased deployment of efficient transformers. The integrated policy strategy should comprise standards and regulations; a institutional structure to monitor, verify and enforce; direct financial assistance and measures to ensure compliance with environmental norms.