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Losses in DC Generator
In all machines, the whole of input energy does not get convertered into output energy. A portion of the input energy gets lost in the machine. DC generator is not exceptional in this case.
Copper Loss
Armature copper loss is given by Ia2 Ra, where Ia is the armature current and Ra is the resistance of the armature. For shunt-wound generators the field copper loss is equal to Ish2 Rsh which is practically constant. For series-wound generators the field copper loss is equal to Ise2 Rse which is also practically constant. For compound-wound generators the field copper loss is equal to Icomp2 Rcomp which is also practically constant. Copper loss is about 20% to 30% of full-load losses. The loss due to brush contact is generally included in armature copper loss.
Core Loss or Iron Loss or Magnetic Loss
Core loss is broadly classified into:
- Hysteresis loss
- Eddy current loss
Hysteresis Loss
The loss occur due to reversal of armature core is said to be hysteresis loss. Each part of the rotor core passes under the north pole N and south pole S alternately and attains S and N polarity, respectively. When the core passes under one pair of poles, the core is said to complete one cycle of frequency reversal. Hysteresis loss ∝ Bmaxn f.
Eddy current Loss
The armature core cuts the magnetic flux during its rotation and emf is induced in the surface of the core, according to the laws of electromagnetic induction. This emf is very small, but it sets up a large current in the surface of the core. This lage current is called the eddy current and the loss is known as the eddy current loss. Eddy current loss ∝ Bmax2 f2.
Core losses are constant for shunt and compound generators, as their field currents are approximately constant. Core loss is about 20 % to 30 % of full-load losses.
Mechanical Loss
- Windage loss or Air friction loss of ratating armature is called as Mechanical loss.
- Friction loss at commutator and bearings, which are about 10 % to 20 % of full load losses.
Stray Loss
- Stray losses is nothing more than the combination of Core losses and Mechanical losses.
- Stray losses are also known a rotational losses.
Related to Losses of DC Generators
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