LOSSES IN DC MACHINE - ELECTRICAL ENCYCLOPEDIA

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LOSSES IN DC MACHINE

We all know that "Energy can neither be created or destroyed, it just changes its forms." In DC Machine whole Input Power is not transformed into Output Power, some part of input power is wasted which is what we call as losses. It decreases the efficiency of DC Machine. 

LOSSES IN DC MACHINE

Main losses in DC Machine are discussed below:

1. Copper Losses

2. Core Losses (Iron Losses)

3. Mechanical Losses

4. Stray Losses


1. COPPER LOSSES

This type of loss occur due to the flow of Electric Current in the Armature and Field Winding of the DC Machine. We know that when current flows in the wire, some power gets dissipated in the form of heat because of the resistance of wire.

Copper Loss in Armature Winding = (Iₐ)2 * Rₐ

where Iₐ = Current in Armature Winding

          Rₐ = Armature Resistance

Copper Loss in field winding in case of DC Shunt Machine = (If)2*Rf

Copper Loss in field winding in case of DC Series Machine = (Ia)2*Rf

   ,  because in case of DC Series Machine field current is equal to the Armature Current

Rf = Resistance of field winding


2. CORE LOSSES (IRON LOSSES)

Since the core of Armature rotates in the magnetic field, so some losses can occur in the core which is called core losses. These losses are almost constant.
They are categorized into two types - Hysteresis and Eddy Current Loss


2.1 HYSTERESIS LOSS

Hysteresis loss occurs due to the reversal of the magnetism in the core. Portion of the armature which is under the North Pole, after completing the half revolution comes under the impact of South Pole and hence magnetic field lines get reversed. This continuous process of magnetic reversal in the armature core consumes some amount of energy which is known as hysteresis loss. Hysteresis Loss depends upon the quality and volume of iron.

Hysteresis loss can reduced by making armature core of silicon steel.

2.2 EDDY CURRENT LOSS

When armature core rotates in the magnetic field, an emf is induced in it as per Faraday's Law of Electromagnetic Induction. This induced emf causes the flow of charge in the core. This current is useless for the machine and is known as Eddy Current. This loss can reduced by making armature core from thin lamination.


3. MECHANICAL LOSSES

These losses includes losses due to the mechanical friction like losses in bearings, windage losses, air resistance etc. These losses are very small.

4. STRAY LOSSES

There are some more miscellaneous losses which are not discussed above comes under the stray losses. Losses like short circuit current in coil during commutation period, distortion of flux, armature reaction etc. 

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