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Transf ormer Heat, Copper and Iron Losses (on photo courtesy of Siemens: Geaf ol-Cast- resintransformer)

http://electrical-engineering-portal.com/transformer-heat-copper-and- iron- losses February 8, 2013

Transformer Heat, Copper and Iron Losses

Edvard

Transformer Losses (Heat)

The thermal ratings of a transformer are determined by the following three factors:

1. The amount o f heat produced in the windings and connections.

2. The amount of heat produced in the iron core.

3. How eff ectively the heat can be removed from the transformer when the thermal ratingof the transformer is reached. At this point, the heat being produced must equal the heat

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Figure 1 - Relationship between Load and Heat Produced inTransf ormer Windings

being removed or dissipated thermal equilibrium.

The ef f iciency ofpower t ransformers is high, especially, fo r large transformers at full load.However, losses are present in all transformers. These losses may be classified as copper or

I2R losses and core or iron losses.

Copper(or Winding) Losses

Copperlosses are resistive and proportional to load current and are sometimes called load

losses or I2R losses.

As the transformer is loaded, heat is produced in the primary and secondary windings

and connections due to I2R. At low loads, the quant ity of heat produced will be small but asload increases, the amount of heat produced becomes signif icant.

At full load, the windings will be operat ing at or near their design temperature. Figure 1 showsthe relationship between load-currentand the heatproduced in t ransformer windings

and connections.

Iron (or Core)Losses

The iron loss is due to strayeddy currents formed in thetransformer core. Lines off lux are formed around thecurrent-carrying

conductors.

The majority of the flux isas indicated in the followingFigure 2, flowing aroundthe core.

Some of the flux however,will t ry to f low at angles to

the core and will causeeddy currents to be set upin the core itself .

http://electrical-engineering-portal.com/what-is-the-eddy-currenthttp://electrical-engineering-portal.com/transformer-extra-losses-due-to-harmonicshttp://electrical-engineering-portal.com/aluminium-or-copper-busbar-trunking-myth-bustedhttp://electrical-engineering-portal.com/download-center/books-and-guides/power-substations/power-transformer-testing-procedures

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Figure 2 - Circulat ing Core Flux

Figure 3 - Transf ormer Core Laminations

The term eddyis used because it isaside from the main f low. To combat t hiseffect, the core is laminated asillustrated in Figure 3. The laminat ionsprovide small gaps between the plates.

As it is easier fo r magnet ic f lux tof low through iron t han air or oil, stray fluxthat can cause core losses is minimized.

Some of the flux however, will t ry to f lowat angles to the core and will cause eddycurrents to be set up in the core itself .

The term eddy is used because it is asidefrom the main f low. To combat thiseffect, the core is laminated asillustrated inFigure 3. The

laminations provide small gapsbetween the plates.

As it is easier fo r magnet ic f lux tof low through iron than air or oil,stray f lux that can cause corelosses is minimized.

What Is Eddy Current?

(VIDEO)

Resource: Science and ReactorFundamentals Electrical CNSCTechnical Training Group