how to minimise energy losses in a transformer

Energy Losses In a Transformer

When we use the equation VpIp = VsIs we are assuming that the transformer is an ideal transformer. An ideal transformer is one which is 100% efficient. In practice, the efficiency of a transformer is less than 100%.
A transformer is designed so that as little energy as possible is lost. There are many ways that a transformer can lose energy.
(a) Power losses occur because the changing magnetic field will also induce currents in the iron core. These induced currents are known as eddy currents. Eddy currents will generate heat and reduce the transformer's efficiency. In order to reduce the formation of eddy currents, a laminated core is used.
(b) Current flowing through th primary and secondary coils will generate heat. Low resistance copper wires is used to reduce this effect.
(c) The core is magnetised and demagnetised alternately when AC current flows through the primary coil. Energy is lost during this process. This is known as Hysterisis. This effect is reduced by using a soft iron core.
(d) There may be a leakage of magnetic flux in the primary coil. A special core design is used in a transformer to ensure that all the primary flux is linked with the secondary coil.

• Resistance of windings – the low resistance copper wire used for the windings still has resistance and thereby contribute to heat loss
• Flux leakage – the flux produced by the primary coil may not be all linked to the secondary coil if the design of the core is bad.
• Eddy currents – the changing magnetic field not only induces currents in the secondary coil but also currents in the iron core itself. These currents flow in little circles in the iron core and are called eddy currents. The eddy currents cause heat loss. The heat loss, however, can be reduced by having the core laminated.(thin sheets of soft iron insulated from one another). (See image below)
• Hysteresis – The msgnetization of the core is repeatedly reversed by the alternating magnetic field. The repeating core magnetization process expends energy and this energy appears as heat. The heat generated can be kept to a minimum by using a magnetic material which has a low hysteresis loss. Hence, soft iron is often chosen for the core material because the magnetic domains within it changes rapidly with low energy loss.

Core loss of a transformer consists of two parts 1)Hysteresis losses 2)eddy current losses. In order to reduce eddy current losses , the magnetic core of the transformer is not made  from a single magnetic material;because in this case the circulating eddy current flowing will be higher.Instead the magnetic core is a stack of thin silicon steel lamination and the laminations are insulated from one an other by thin layer of varnish  in order to reduce eddy current and hence eddy current losses.

In order to minimize hysteresis losses , soft magnetic materials eg: Si steel, steel alloys ,Mn-Zn ferrite are used because they have high saturation magnetization, Low coercivity ,High magnetic permeability etc. which reduce losses due to hysteresis

The design approaches for reduction of transformer losses are well known and proven. Generally they consists of the following:

1. Using more material
2. Better material
3. New Material
4. Improved distribution of materials
5. Improvement in cooling medium and methods

Each design tries to achieve desired specifications with minimum cost of materials or minimum weight or volume or minimum overall cost of ownership. Worldwide, more and more consumers are now purchasing transformers based on the total ownership costs, than just the first cost

Minimising Iron Losses

Losses in Core

Choice of metal is critical for transformer cores, and it’s important that good quality magnetic steel be used. There are many grades of steel that can be used for a transformer core. Each grade has an effect on efficiency on a per-kg basis. The choice depends on how you evaluate non-load transformer losses and total owning costs.
Almost all transformer manufacturers today use steel in their cores that provides low transformer losses due to the effects of magnetic hysteresis and eddy currents. To achieve these objectives, high permeability, cold-rolled, grain-oriented, silicon steel is almost always used. Construction of the core utilizes step lap mitered joints and the laminations are carefully stacked