The iron losses in a d.c. motor depends upon ………………..

The iron losses in a d.c. motor depends upon ....................

Right Answer is:

Both flux and speed


Core Losses

Core losses are also known as iron losses or Magnetic losses. These Losses are constant and independent of the load. They are induced in the machine due to hysteresis and eddy currents produced in the core produced when the magnetization is changing. They mainly occur in the armature teeth and core as also in the pole shoe.

Hysteresis losses occur due to the reversal of the magnetization of the armature core. So, the hysteresis loss can be obtained as:

Hysteresis Loss = Kh × BM1.67 × f × v watts

Kh = Hysteresis constant depends upon the material
Bm = Maximum flux density
f = frequency
v = Volume of the core

The eddy current loss exists due to eddy currents. When the armature core rotates, it cuts the magnetic flux and e.m.f. gets induced in the core. This induced e.m.f. sets up eddy currents which cause the power loss. Ibis loss is given by,

Eddy current losses = Ke × Bm2 × f2 × t2

Where Ke = Eddy current constant
t = thickness of the core

Hence from the above equation flux is dependent on the square of the excitation flux, which determines magnetic induction. In addition, the losses are dependent upon the speed of rotation because the field pulsates with respect to the iron sheets with a frequency that is equal to the angular speed of the rotor. The iron losses within the rotor are denoted by PFe. They exist even in cases when the armature winding is disconnected and does not have any current.

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