Loose brush contact

Armature resistance is more

Field resistance is above critical resistance

Prime mover is running at above rated speed

Shunt generator

Series generator

Compound generator

Self excited generator

Reduce the air gap

Increase the field strength

Minimize the magnetic losses

Spread out flux uniformly in the air gap

Maintain constant voltage

Collects the current unidirectionally

Reduces the voltage drop at brushes

Increases the terminal voltage than rated

Steel and graphite

Carbon and graphite

Cast iron and graphite

Aluminium and graphite