Monday, 30 November 2015

Different method for correction of power factor


Losses In Transformer


Losses In Transformer
 An electrical transformer is an static device, hence mechanical losses (like windage or friction losses) are absent in it. A transformer only consists of electrical losses (iron losses and copper losses). Transformer losses are similar to losses in a DC machine, except that transformers do not have mechanical losses.
Losses in transformer are explained below -
(I) Core Losses Or Iron Losses
Eddy current loss and hysteresis loss depend upon the magnetic properties of the material used for the construction of core. Hence these losses are also known ascore losses or iron losses.
§  Hysteresis loss in transformer: Hysteresis loss is due to reversal of magnetization in the transformer core. This loss depends upon the volume and grade of the iron, frequency of magnetic reversals and value of flux density. It can be given by, Steinmetz formula:
Wh= ηBmax1.6fV (watts)       where,   η = Steinmetz hysteresis constant
                                                     V = volume of the core in m3
§  Eddy current loss in transformer: In transformer, AC current is supplied to the primary winding which sets up alternating magnetizing flux. When this flux links with secondary winding, it produces induced emf in it. But some part of this flux also gets linked with other conducting parts like steel core or iron body or the transformer, which will result in induced emf in those parts, causing small circulating current in them. This current is called as eddy current. Due to these eddy currents, some energy will be dissipated in the form of heat.
 (Ii) Copper Loss In Transformer
Copper loss is due to ohmic resistance of the transformer windings.  Copper loss for the primary winding is I12R1 and for secondary winding is I22R2. Where, I1 and I2 are current in primary and secondary winding respectively, R1 and R2 are the resistances of primary and secondary winding respectively. It is clear that Cu loss is proportional to square of the current, and current depends on the load. Hence copper loss in transformer varies with the load.
Efficiency of Transformer
Just like any other electrical machine, efficiency of a transformer can be defined as the output power divided by the input power. That is  efficiency = output / input .Transformers are the most highly efficient electrical devices. Most of the transformers have full load efficiency between 95% to 98.5% . As a transformer being highly efficient, output and input are having nearly same value, and hence it is impractical to measure the efficiency of transformer by using output / input. A better method to find efficiency of a transformer is using, 
efficiency = (input - losses) / input = 1 - (losses / input).
Condition For Maximum Efficiency
Let,Copper loss = I1 2R1 & Iron loss = Wi 

Hence, efficiency of a transformer will be maximum when copper loss and iron losses are equal.
         That is Copper loss = Iron loss.


TRANSISTORS

TRANSISTORS A transistor is a semiconductor device that contains three regions separated by two distinct PN junctions. The two junctions are...

Translate