In general Transformers are classified in two categories,Power transformer and Distribution transformer. As name suggest power transformers are used for network of higher voltage for power supplies say 400KV, 200KV, 110KV, 66KV, 33KV while Distribution transformers are used for lower voltage distribution network say 11KV, 6.6KV, 3.3KV,420V,230V.
The efficiency of transformer is typically between 94 to 96%, the efficiency of transformer not only depends on design but for operating also.
Transformer loss consist of two components ;-
- No load Losses (core losses) is the efficiency loss required to maintain magnetic field in the transformer’s steel core. This loss is independent of load and shall be constant thought load.
Hysteresis and eddy current loss are two causes of no load losses. Hysteresis loss is that energy lost by reversing the magnetic field in the core as the magnetizing rises, and falls and reverse direction. Eddy current losses is a result of induced current circulating in the core.
- Load Losses ( copper losses) is associated with the full load current flow in the transformer winding. Copper loss is the power lost in primary and secondary winding of transformer due to ohmic resistance of the winding. copper loss varies with the square of the load current (P=I2R)
Typical loss is shown in the fig
As shown in fig transformer has highest efficiency at part load condition, typically at 40-60% loading.
Transformer supplier can supply values of both no load losses LNL and load losses LL
Total loss LT can be easily calculated by LT = LNL +LL*(%Load/100)2
Or Total Loss = No load Loss +Load loss X (KVA Load/KVA rated)2
Source : Simens energy management handbook