Losses in DC Machines

The losses in DC machines are divided into five basic categories. These various losses are copper loss or I²R loss, Iron loss or core loss, mechanical loss, Brush Loss and stray loss. All this losses are explained in detail below.

Table of Contents

Various losses in dc machines are shown in tree diagram which is given below.

Que. List the various losses on a DC Motor.

The various losses on a DC Motor are,

1) Winding losses (Copper losses)

Armature winding losses
Shunt field losses
Series field losses

2) Core losses (iron losses)

3) Mechanical loss

Brush contact losses
Windage and frictional

Copper or Electrical Losses

The copper losses occur due to the resistance offered by the winding. Generally winding is made up of copper. Hence, these losses are also referred as winding losses.
This loss is also called as variable loss, because this loss mainly depend upon current and current can change with load on machine.
Mathematically, copper losses can be given as I²R.
Armature copper losses, I_a²R_a, are around 30% of the total full-load losses.
Similarly shunt copper losses are I_sh²R_shand series copper losses are I_se²R_se.

Core Losses or Iron Losses

These losses are due to hysteresis or the eddy current losses.
Such losses are also called as magnetic losses, and also this loss is called as constant loss.
When the dc machine is operated at constant flux density and at constant speed, these losses do not very much.

Brush Loss

Power losses also occurs at point of constant between copper commutator and the carbon brush.
This loss is also very small as compared with all other losses in machine.

Mechanical Loss

Losses occurring due to mechanical affects, like friction etc. are called as mechanical losses.
Mechanical losses include bearing friction loss and windage loss.
These losses are very small in magnitude as compared to copper loss and iron loss.

Stray Loss

all losses which is discus above are classified under stray loss. These loss also called as miscellaneous loss because they depend on factor like distortion in flux, current variation due to armature reaction etc.

Generally these losses are consider to be in very small value is 1% nearly of full load power output.