What happens to the brushes in an alternator when field current is low?

When the field current in an alternator is low, the brushes can move freely. This is because the magnetic field strength generated by the field windings of the alternator is proportional to the field current. A low field current means a weaker magnetic field, which can affect the tension and pressure exerted by the brushes against the slip rings. As the magnetic field strength diminishes, it reduces the overall dynamic interaction between the rotating and stationary components, allowing the brushes to move more freely rather than being held tightly in a fixed position. This is an important consideration for maintenance and operation, as free movement of brushes can impact the overall efficiency and performance of the alternator.