What is the relation of the copper loss and brush contacts with the total loss in universal commutator motors?

Copper loss and brush contacts play a significant role in the total loss in universal commutator motors. To explain the relationship in detail:

1. Copper loss: This type of loss occurs due to the resistance in the windings of the motor. Universal commutator motors have windings on both the stator and the rotor through which current flows. The resistance of these windings to the electric current generates heat, which represents energy lost. This energy is not contributing to the motor’s output (mechanical energy) and is instead dissipated as heat. Copper loss is directly proportional to the square of the current flowing through the windings (P = I^2R where P is the power loss, I is the current, and R is the resistance). Since universal motors typically operate at high speeds and can carry significant current, especially under load, the copper losses can be substantial.

2. Brush contacts: Brush contacts in a universal motor are where the electrical connection is made to the rotating commutator. These brushes face frictional losses and also experience electrical losses due to contact resistance. The frictional loss contributes to mechanical loss, whereas the electrical loss is considered part of the copper loss but is specific to the brush-commutator interaction. Every time the brush passes over a commutator segment, there’s a small voltage drop across the brush, termed as brush contact drop, contributing to the total loss alongside generating heat and causing wear on both the brushes and the