Magnetic Loss in Transformer

All transformers dissipate some energy in the process of transformation. Operating principles dedicate that the magnetic core is always magnetized to the same level, regardless the load. This means that even when transformer works with no load, the magnetic losses are almost the same as when it is operating at full load.

At full load, the efficiency of large power transformers can be very high- above 99% in some cases. However, because the magnetic loss is piratically fixed, efficiency reduces with the load. Inevitable, under no load conditions any transformer operates with 0% efficiency- it consumes some energy to remain energized, but it delivers no energy to any load.

The electricity transmission grid and all the transformers in it are exposed to varying load. At night the load is relatively light, so the transformers operate at much less the nominal conditions, but they keep dissipating exactly the same energy in  magnetic losses.

When transformers were first invented, magnetic cores were made from so-called "soft iron". This material was quite loss and ever since, engineers and scientists have been striving to improve efficiency by introducing a number of technological modification- to chemical structure, mechanical processing, annealing, post-processing, etc.

Now a days, the most commonly used material for magnetic cores of power transformers is electrical steel, which is a descendant of soft steel. However, the power loss of the best grade of electrical steel now in use is around 50 times lower than that of soft steel. This has had a very significant impact on the overall efficiency of power transformers.

In some cases, medium voltage power transformers are still in use after 50 years of operation. Because these old transformers were made from inferior magnetic material, their losses are much higher and replacing them with modern units would most likely bring noticeable saving  in the energy distribution network- a transformer made 50 years ago could lose 5-10 times more energy ( for magnetic loss ) than a modern equivalent with the same rating.

The production of the grain - oriented electrical steel is a very complex process ( perhaps a topic for a future article). Further improvements are on the horizon, but currently are too expensive to implement. However, another approach is possible - different material can be used.

To ensure correct operation, several properties of transformers must be tested regularly, electric insulation, degradation of oil, turn and voltage ratio, etc. Higher losses in the magnetic core can influence to some degree the voltage ration or the phase shifts between the test signals. However, this is usually not a problem because correctly designed transformer testers can cope with these effects, even for older transformers.

Study and research continue in the problem of losses in magnetic materials. Manufacturers of electrical steel and amorphous ribbon sponsor many of these studies are done and in progress in "magnetic" where the newest developments are presented.

In future we can expect even better and more efficient magnetic cores. The improvements might not be ground breaking, but every single percentage point counts for efficiency , for running cost and for the environment.