# Losses in DC Machine

As we know “Energy neither can be created nor it can be destroyed, it can only be transferred from one form to another”. In DC machine, mechanical energy is converted into the electrical energy. During this process, the total input power is not transformed into output power. Some part of input power gets wasted in various forms. The form of this loss may vary from one machine to another. These losses give in rise in temperature of machine and reduce the efficiency of the machine. In **DC Machine**, there are broadly four main categories of energy loss.

## Copper Losses or Electrical Losses in DC Machine or Winding Loss

The copper losses are the winding losses taking place during the current flowing through the winding. These losses occur due to the resistance in the winding. In DC machine, there are only two winding, armature and field winding.Thus copper losses categories in three parts; armature loss, field winding loss, and brush contact resistance loss. The copper losses are proportional to square of the current flowing through the winding.

### Armature Copper Loss in DC Machine

Armature copper loss = I_{a}

^{2}R

_{a}Where, I

_{a}is armature current and R

_{a}is armature resistance. These losses are about 30% of the total full load losses.

### Field Winding Copper Loss in DC Machine

Field winding copper loss = I_{f}

^{2}R

_{f}Where, I

_{f}is field current and R

_{f}is field resistance. These losses are about 25% theoretically, but practically it is constant.

### Brush Contact Resistance Loss in DC Machine

Brush contact loss attributes to resistance between the surface of brush and commutator. It is not a loss which could be calculated separately as it is a part of variable losses. Generally, it contributes in both the types of copper losses. So, they are factor in the calculation of above losses.## Core Losses or Iron Losses in DC Machine or Magnetic Losses

As iron core of the armature is rotating in magnetic field, some losses occurs in the core which is called core losses. Normally, machines are operated with constant speed, so these losses are almost constant. These losses are categorized in two form; Hysteresis loss and Eddy current loss.### Hysteresis Loss in DC Machine

Hysteresis losses occur in the armature winding due to reversal of magnetization of the core. When the core of the armature exposed to magnetic field, it undergoes one complete rotation of magnetic reversal. The portion of armature which is under S-pole, after completing half electrical revolution, the same piece will be under the N-pole, and the magnetic lines are reversed in order to overturn the magnetism within the core. The constant process of magnetic reversal in the armature, consume some amount of energy which is called hysteresis loss. The percentage of loss depends upon the quality and volume of the iron.#### The Frequency of Magnetic Reversal

Where, P = Number of poles N = Speed in rpm#### Steinmetz Formula

The Steinmetz formula is for the calculation of hysteresis loss. Where, η = Steinmetz hysteresis co-efficient B_{max}= Maximum flux Density in armature winding F = Frequency of magnetic reversals V = Volume of armature in m

^{3}.