Since the transformer is a static machine it doesn't contain any moving or rotating parts as compared to an induction motor. So there are no friction and windage losses due to bearings and due to air resistance. Hence, the various types of losses of a transformer occurring in the windings and core material are,
- Iron or core losses
- Hysteresis loss
- Eddy current loss
- Copper or Winding Loss
- Stray loss
- Dielectric loss.
- Hysteresis loss
- Eddy current loss
Iron or Core Losses :
The losses in the magnetic core which links both the windings by magnetic induction are called iron or core losses of the transformer. The iron practically remains constant under all load conditions i.e., they are independent or irrespective of the load condition. Hence, the iron losses are also called constant losses, and they are composed of two losses. They are,
- Hysteresis loss
- Eddy current loss
Hysteresis Loss :
Since the supply given to the transformer is alternating, the nature of the magnetic flux in the core will be also in alternating nature. Due to this, the randomly oriented magnetic domains which behave like a small magnet will be oriented in the direction of MMF applied. As the nature of magnetic flux applied is alternating the core material undergoes a cycle of magnetization and demagnetization effect.
Due to this, the one directionally oriented domain will take the reverse direction for every cycle. So that there will be extra energy consumed in the form of power loss known as 'Hysteresis Loss'. The expression for hysteresis loss is given by,
Where,- Kh = Hysteresis constant depends upon the type of core material used
- Bm = Maximum flux density
- f = Supply frequency
- V = Volume of the core material.
Eddy Current Loss :
The core of the transformer is made up of conducting material. The laminated sheets which form the core limb will induce their own emf in each sheet when subjected to alternating flux. This results in the circulation of currents in each sheet and causes power loss known as 'Eddy Current Loss'. It is given by,
Where,- Ke = Hysteresis constant depends upon the type of core material used
- Bm = Maximum flux density
- f = Supply frequency
- t = Lamination thickness.
Since the frequency and flux density of the core material remain constant these losses are also called Constant losses. Therefore, the total iron or core or constant loss is the sum of both hysteresis and eddy current losses.
Minimization of Iron Losses :
- The hysteresis losses of the transformer cannot be eliminated completely but can be reduced by choosing a low hysteresis coefficient material like silicon steel.
- The eddy current losses can be reduced by making very thin laminations of silicon steel.
Copper Loss or Winding Loss :
We know that every material possesses some resistance even if it can be of conducting type. This resistance causes power loss (I2 R) in the conducting material used for the windings of the transformer. The conducting material used for winding is mostly copper, hence it is called Copper Loss. The copper loss of the transformer is expressed as,
Where,- I12 R1 = Power in the primary winding due to primary current and resistance
- I22 R2 = Power in the secondary winding due to secondary current and resistance
It is clear that copper loss is proportional to the square of the current i.e., copper loss at half full load is one-fourth of that at full load. As the current depends upon the load connected to the transformer. The copper loss varies with variation in load and is also called Variable Loss.
Stray Loss :
The transformer works on the principle of mutual induction i.e., emf induced in the secondary winding is by linkage of flux produced by the primary winding. But, in practice, all the flux produced by the primary winding does not link with secondary winding completely. There will wastage of flux which does not link with secondary winding as the leakage. This leakage flux will cause some losses in the transformer known as Stray Loss.
Dielectric Loss :
As the name suggests these losses depend upon the dielectric strength of the insulating medium used in the transformer (generally oil). Due to the continuous operation of the transformer, the dielectric material used losses its dielectric strength and causes some losses which reduces the overall efficiency of the transformer. These losses can be minimized by periodic testing of the insulating material used.