amorphous core transformers: a smart solution

amorphous-core
An amorphous core transformer from ABB image courtesy ABB

By Paul Grad, engineering writer

Large amounts of energy could be saved and a significant reduction in the amount
of greenhouse gas emissions could be achieved through the use of amorphous core –
also called amorphous metal – distribution transformers.

Even though modern power transformers are very efficient, up to 3 per cent of all electrical power generated is wasted in transformer losses, representing 40 per cent to 50 per cent of all transmission and distribution losses in a typical power grid.
“Loss” is the difference between input and output power. The efficiency of a transformer is the output power divided by the input power. Most transformers have full load efficiency between
95 per cent and 98.5 per cent. The efficiency is usually measured as input-losses/input, i.e. 1-(losses/input).

Although in Australia only a relatively small number of those transformers have been installed, several other countries have already a large number of those transformers installed and operating and some countries intend to use only amorphous core distribution transformers.

Conventional transformers have a core assembled from stacks of laminations made of silicon steel with a fairly uniform crystalline structure. In amorphous core transformers, a ribbon of steel is wound, usually into a rectangular toroid shape, to form the core. In those transformers, the typical material (called Metglas) is an alloy of iron with boron, silicon and phosphorus. This material is made by melting the metal and then cooling it very quickly before it has time to crystallise. It is the special properties of this material that lead to a reduction in electrical losses.

The losses in a transformer are core losses (or iron losses), which constitute most of the no-load losses and copper losses. The no-load losses in a transformer are mainly the core losses.

Core losses include hysteresis losses and eddy current losses. Hysteresis loss is due to reversal of magnetisation in the transformer core.

The big benefit of the amorphous core material is it has lower hysteresis losses, which means less energy is wasted in magnetising and demagnetising it during each cycle of the supply current. The no-load loss in amorphous core transformers is about 70 per cent of that of conventional transformers.

Eddy currents are currents created by the induced emf in parts of the transformer other than the secondary winding, causing some energy dissipation as heat. Amorphous cores have higher electrical resistance than conventional cores and thus, losses due to eddy currents in the core are also reduced.

The copper losses are due to the ohmic resistance of the transformer windings. Copper loss is proportional to the square of the current and the current depends on the load, and therefore copper loss in a transformer depends on the load.

A transformer’s efficiency is at a maximum when copper losses and iron losses are equal.

For example, comparing silicon steel transformers with amorphous core transformers produced by Hitachi, in those of capacity 100kVA the no-load loss is 68 per cent lower for amorphous core transformers, 74 per cent lower for 500kVA transformers, and 74 per cent lower for 1MVA transformers.

In the case of transformers produced by ABB Group, no-load loss is 75 per cent lower for amorphous core transformers of 250kVA, 77 per cent lower for transformers of 400kVA, and 77 per cent lower for transformers of 630kVA.

Preformed Line Products of Glendenning, NSW, produces amorphous core transformers of up to 167kVA single phase and up to 1MVA three phase. The transformers reduce the no-load losses by up to 75 per cent compared with conventional transformers.

Powerstar Australia of Melbourne produces its HV Max amorphous core transformer with ratings 500kVA to 2MVA. The company claims the transformers are 99 per cent efficient.

There are more than 80 million distribution transformers in use worldwide, of which about 4.6 million are in the European Union. Australia operates about 700,000 distribution transformers. The potential for energy savings are very significant.

Throughout the world, network losses, i.e. transmission and distribution losses, as percentage of the power delivered to the grid by the utilities, vary widely. The losses are generally lower in the developed countries than in developing countries. For example, according to the International Energy Agency, the losses are 6 per cent in the US, 5 per cent in Australia, 8 per cent in the UK, 5 per cent in France, 3 per cent in Finland, 4 per cent in Germany, 3 per cent in Israel, and 5 per cent in Japan.

The losses are usually much higher in developing countries, for example: they are 16 per cent in Brazil, 21 per cent in India, 35 per cent in Iraq, 17 per cent in Kenya, 15 per cent in Mexico, 34 per cent in Nepal, 22 per cent in the Sudan, and 20 per cent in Venezuela.

There are exceptions. The losses are quite low in some developing countries, for example: 6 per cent in China, 6 per cent in Malaysia, 6 per cent in Paraguay, 6 per cent in Peru, and 4 per cent in Zimbabwe.

According to the Energy Information Administration and the European SEEDT (Strategy for Development and Diffusion of Energy-efficient Distribution Transformers), potential annual savings with amorphous core distribution transformers are 27TWh in the US, 20TWh in the European Union, 14TWh in China, and 3TWh in Australia. The potential annual carbon dioxide reduction in millions of tons is 17 in the US, 10 in the European Union, 12 in China and three in Australia. China and India could together save up to 30TWh annually, and reduce up to 30 million tons of carbon dioxide emissions by using amorphous core distribution transformers.

China has embarked upon a large effort to improve its energy efficiency. Several Chinese organisations have teamed up with Action Sustainable Development (ASD-France) to improve the energy efficiency in China’s transformers and power distribution systems. This effort, announced in December 2010, focuses on using higher efficiency transformers. China has installed more than 70 million kVA of amorphous core transformers.

India has also been conducting a major effort to improve energy efficiency and has widely adopted amorphous core transformers. India’s installed amorphous core transformer capacity is more than 35 million kVA.

Amorphous core transformers are also widely used in the US, Japan, and Europe, but they have not yet caught on in Australia. A few Australian utilities have installed some of those transformers on a more or less experimental basis.

Essential Energy has trialled a small number of those transformers but does not use them widely in its network. Ausgrid has been trialling five amorphous core distribution transformers for two years in the Central Coast of NSW and the Hunter Valley. The utility wants to be prudent about committing itself to employing those transformers, and is carefully considering the economics of their operation.

Endeavour Energy has been trialling amorphous core transformers since 2008. It is now using those transformers for the pole-mounted distribution transformers, which are less than 100kVA. The amorphous core transformers are somewhat larger and heavier than conventional transformers, which is one of the reasons why the utility limited the use of amorphous core transformers for pole-mounted substations for capacity greater than 100kVA. Endeavour Energy said it has not used those transformers in pad-mounted substations as, at the current process, the “whole of life cost” comparison does not justify their use for the larger transformers.

Ergon Energy has used several amorphous core transformers in its network, including single-phase 10kVA, 25kVA and 50kVA transformers, and three-phase 25kVA, 63kVA and 100kVA transformers.

There are a number of incentives for introducing high efficiency transformers in Australia, including ever more stringent regulations. From October 1, 2004, distribution transformers manufactured in or imported into Australia must comply with Minimum Energy Performance (MEPS) requirements, which are set out in AS 2374.1.2-2003. The intention of MEPS is to increase energy efficiency by eliminating low efficiency transformers from the market and to encourage the use of high efficiency transformers. The requirements were upgraded in 2006 in MEPS 2.

One of the objections to the introduction of amorphous core transformers is that they are more expensive than their conventional counterparts. The payback period for the extra cost is usually three to five years. However, if energy prices increase, which seems likely, this period will become shorter.

The savings, which can be achieved with amorphous core transformers, seem small in percentage terms, but they are very significant in terms of kWh of energy and tonnes of carbon dioxide saved annually.