For every engineer the most important thing to know about any machine is losses which is the most important aspect to change the efficiency of a machine. So In this post i want to discuss about the losses that are effecting the efficiency of the machine.
To reduce the losses in the generator and improve the efficiency we have to know the sources and causes of the losses. There are different types of losses occurring in the generator at different parts of the generator.
Losses in D.C generator can be divided into three categories they are
1) Iron Losses
2) Copper Losses
3) Mechanical Losses
To reduce the losses in the generator and improve the efficiency we have to know the sources and causes of the losses. There are different types of losses occurring in the generator at different parts of the generator.
Losses in D.C generator can be divided into three categories they are
1) Iron Losses
2) Copper Losses
3) Mechanical Losses
Iron losses:
Due to rotation of iron core of the armature in the magnetic flux of the field poles, there are some losses taking place continuously in the core and are known as Iron losses or Core losses.Iron losses consists of
- Hysteresis Losses
- Eddy Current Losses
Hysteresis Losses:
This loss is due to the reversal of magnetisation of the armature core. Every portion of the rotating core passes under north and south pole alternatively, there by attaining south and north poles respectively. The core undergoes one complete cycle of magnetic reversal after passing under one pair of poles.
If P is the number of poles and N the armature speed in r.p.m then frequency of magnetic reversals is f = PN/120.
The loss depends upon the volume and grade of iron, maximum value of flux density Bmax and frequency of magnetic reversals. Hysteresis loss is given by steinmetz formula.
Wh = ƞ( Bmax)^1.6 fv watts
If P is the number of poles and N the armature speed in r.p.m then frequency of magnetic reversals is f = PN/120.
The loss depends upon the volume and grade of iron, maximum value of flux density Bmax and frequency of magnetic reversals. Hysteresis loss is given by steinmetz formula.
Wh = ƞ( Bmax)^1.6 fv watts
Eddy current losses:
When the armature core rotates, it also cuts the magnetic flux. Hence , an emf is induced in the body of the core according to the electromagnetic induction. This emf though small induces large current in body of the core due to its small resistance. This current is known as eddy current.The power loss due to flow of this current is known as eddy current loss.
This losses will be considerably high if the core we used is solid. In order to reduce eddy current the core should be laminated with thin lamination. These core laminations are insulated from each other by a thin coating of varnish.
eddy current losses We = K(Bmax)^2 f^2 t^2 V^2 watts
From the above equation we can say that the eddy currents depends on thickness of lamination. so to reduce eddy current losses we have to use thin lamination.
eddy current losses We = K(Bmax)^2 f^2 t^2 V^2 watts
From the above equation we can say that the eddy currents depends on thickness of lamination. so to reduce eddy current losses we have to use thin lamination.
Copper losses:
This losses also called as variable losses. This losses depend upon the current and it will be varying depending upon the load conditions. so it is called as variable losses.
Copper losses can be sub-divided as follows.
Copper losses can be sub-divided as follows.
- Armature copper losses
- Field copper losses
- brush losses
Armature copper losses = Ia^2 Ra
Field copper losses = Ish^2 Rsh
brush losses will be around 1 V
Mechanical losses:
These consists of
- Friction losses at bearing and commutator
- air-friction losses or windage losses of rotating armature
Magnetic and mechanical losses are collectively called as stray losses or rotational losses.
This are the total losses that occur in dc generator, if you have any suggestions please comment below
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