What are the Various Losses in DC Machine?

We know that DC motor is used to change the power from electrical form to mechanical form similarly; dc generator is used to change the power from mechanical form to electrical form. The input power in the DC generator is in mechanical form and output power is in electrical form. In contrast, the input power of the DC motor is electrical form and output power is in mechanical form. Bu practically, while converting input power to output power, there is a loss of power. So machine efficiency can be reduced. Efficiency can be defined as the ratio of output power and input power. Therefore, to design a rotary dc machine with high efficiency, then it is significant to know the losses occurring in a dc machine. There are different types of losses occurring in the DC machine which are discussed below.

Losses in DC Machine

There are different kinds of losses that occur in the DC machine which is generated in different ways. But these losses can cause heating and major effects. The temperature can be enhanced within the machine. So the life and performance of the machine can be reduced especially insulation. Therefore, the rating of the DC machine can be affected directly through different losses. The different types of losses which are occured in the DC machine are discussed below.

Electrical or Copper Losses in DC Machine

Electrical/copper can occur within the windings of the DC machine-like field copper or armature. These types of losses mainly include different losses like filed copper loss, armature copper loss & loss because of the resistance of brush contact

Here, armature copper loss can be derived as Ia²Ra²

Where,

‘Ia’ is armature current

“Ra’ is the resistance of Armature

This kind of loss will give about 30% to 40% to full load losses. This loss is changeable & mainly depends upon the quantity of the dc machine load.

Filed copper loss can be derived as If2Rf

Where,

‘If’ is the field current whereas the Rf is the field resistance)

In a shunt wounded field, practically the field copper loss is stable and it donates 20% to 30% to full- load losses.
The resistance of brush contact contributes toward the copper losses. Usually, this kind of loss comes under armature copper loss.

Magnetic Losses or Core Losses or Iron Losses

Alternate names of these losses are iron losses or core losses. These kinds of losses can occur within the armature core & teeth wherever the flux can be changed. These losses include two losses namely hysteresis and eddy current losses.

Hysteresis Losses

This loss can be occurred because of the reverse magnetism in the armature core.

P_h = Ƞ^B1.6_maxfV watts

Here, ‘Bmax’ is the highest flux density value within the core.

‘V’ is the armature core volume

‘F’ is the reverse magnetism frequency

‘η’ is the co-efficient of hysteresis

Hysteresis losses can occur within the teeth and armature core of the dc machine. This loss can be reduced through Silicon steel core material. This material has less hysteresis coefficient.

Eddy Current Loss

Once the armature core turns in a magnetic field of the pole and cuts the magnetic flux. Therefore, an e.m.f can be induced within the core body based on the electromagnetic induction laws. The induced e.m.f can be set up current within the armature core body, so this is called as eddy current. And the loss of power because of the current flow is called eddy current loss. This loss can be derived as

The eddy current loss is given by

Eddy Current loss Pe=K_eB²_maxf²t²V Watts

From the above equation

‘Ke’ is constant, which depends on the core resistance & system of unit utilized.

‘Bmax’ is the maximum flux density within wb/m2

‘ T’ is the lamination thickness in ‘m’

‘V’ is the core volume in ‘m3’

These losses can be reduced by making the armature core with thin laminated stamps. So the lamination thickness which is used in armature core can be 0.35 m to 0.5 mm.

Brush Losses

These losses can occur between the carbon brushes & the commutator. This is the power loss at the contact end of the brushes in the dc machine. This can be expressed as

P_BD = V_BD * I_A

Where

‘PBD’is the loss of brush drop

‘VBD’ is the voltage drop of the brush

‘IA’ is the armature current

Mechanical Losses

Mechanical losses can be occurred due to the effects of the machines. These losses are separated into two losses namely bearing friction & windage. These kinds of losses can occur at the moving parts within the dc machine. The air in the DC machine is also called as windage losses.

Windage losses are extremely small and these can be occurred because of the fiction in bearing. These losses are also known as mechanical losses. These losses include brush friction and bearing, windage loss otherwise air fiction rotary armature. In total full load losses, these losses have occurred about 10% – 20%.

Stray Losses

These are mixed type of losses and the factors considered in these losses are

The distortion of flux due to armature reaction

The short circuit within the coil

Because of the eddy current within the conductor, there is an extra copper loss

These kinds of losses cannot be determined. So, it is essential to allocate the logical value of this loss. In most of the machines, these losses are assumed to be 1%.

How to Minimize Loses In DC Machine?

Losses in DC machines mainly occur from three different sources like resistive, magnetic & switching. To reduce magnetic and hysteresis losses, cover the magnetic core so that eddy currents can be prevented. Resistive losses can be reduced based on careful design because to fill the cross-sectional area with wire, the size of the wire, and the insulation thickness is significant.

Thus, this is all about an overview of different types of losses in dc machine. The losses in the dc machine are mainly separated into five categories like electrical/copper, magnetic/core/iron, brush, mechanical, and stray. Here is a question for you, what are constant & variable losses?