Question

list the losses in the series and parallel DC motors, and to which they are attributed.

Answer 1

the losses in series and parallel dc motors are:

1.copper losses:the copper losses are the winding lossestaking place during the current flowing through the winding.the losses are due to the resistance of winding.in dc machine there are only two winding:field and armature.the cu losses are categaries in three part which are cu losses in armature in field in brush contact drop.the cu losses are directly proportional to square of current.total losses 30%losses are due to armature winding cu losses,25%losses are due to field winding,

2.CORE 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.

Eddy Current Loss in DC Machine

According to Faraday’s law of electromagnetic induction, when an iron core rotates in the magnetic field, an emf is also induced in the core. Similarly, when armature rotates in magnetic field, small amount of emf induced in the core which allows flow of charge in the body due to conductivity of the core. This current is useless for the machine. This loss of current is called eddy current. This loss is almost constant for the DC machines. It could be minimized by selecting the laminated core.

3.Mechanical Losses in DC Machine

The losses associated with mechanical friction of the machine are called mechanical losses. These losses occur due to friction in the moving parts of the machine like bearing, brushes etc, and windage losses occurs due to the air inside the rotating coil of the machine. These losses are usually very small about 15% of full load loss.

4.Stray Load Losses in DC Machine

There are some more losses other than the losses which have been discussed above. These losses are called stray-load losses. These miscellaneous losses are due to the short-circuit current in the coil undergoing commutation, distortion of flux due to armature and many more losses which are difficult to find. These losses are difficult to determine. However, they are taken as 1% of the whole load power output.