What do self-exciting voltage regulators use to retain residual magnetism?

Self-exciting voltage regulators utilize soft iron to retain residual magnetism because soft iron has high magnetic permeability and can easily become magnetized and demagnetized. This property allows it to effectively retain a certain level of magnetism even after the power supply has been turned off.

In self-exciting setups, the initial residual magnetism present in the iron core is crucial to the operation of the voltage regulator. When the generator starts, the existing magnetism induces a voltage, which helps to excite the field windings. This process creates a feedback loop that sustains the voltage output, allowing the system to maintain stable operation. The use of soft iron enhances this function because it enables quicker response to changes, which is essential for maintaining consistent voltage levels.

In contrast, while other materials like copper alloys, permanent magnets, and electromagnets have their uses in electrical applications, they do not possess the same desirable characteristics for retaining residual magnetism in self-exciting voltage regulators as soft iron does.