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Losses in DC Machine- Types of Losses

In DC machines (generator or motor), the losses may be classified into 4 categories namely,

  1. Copper losses
  2. Iron or core losses
  3. Mechanical losses
  4. Stray Losses

1. Copper Loss in DC Machine

In dc machines, the losses that occur due to the resistance of the various windings of the machine are called copper losses. Copper losses are also known as I2R losses because these losses occur due to current flowing through the resistance of the windings.

The major copper losses that occur in dc machines are as,

a) Armature copper loss = Ia2Ra
Where, Ia is the armature current and Ra is the armature winding resistance.
b) Field winding copper loss = If2Rf
Where, If is the field current and Rf is the field winding resistance.
In shunt machine, the copper loss in the shunt field is I2shRsh, where Ish is the current in the shunt field, and Rsh is the resistance of the shunt field windings. The shunt regulating resistance is included in Rsh.
In a series machine, the copper loss in the series windings is I2seRse, where, Ise is the current through the series field windings, and Rse is the resistance of the series field windings.

In dc machines, there is also a brush contact loss due to brush contact resistance. In practical calculation, this loss is generally included in armature copper loss.

2. Iron or core losses in DC Machine

The iron losses occur in the core of the armature of a DC machine due to the rotation of the armature in the magnetic field. Because these losses occur in the core of the armature, these are also called core losses.

There are two types of iron or core losses namely hysteresis loss and eddy current loss.

3. Mechanical Loss in DC Machine

Mechanical losses are divided into bearing friction loss and windage loss. The losses occurring in the moving parts of the machine and the air present in the machine is known as Windage losses. These losses are very small.

4. Stray Losses in DC machine

The following factors are considered in stray load losses.

  • The distortion of flux because of the armature reaction.
  • Short circuit currents in the coil, undergoing commutation.



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