Final answer:
OPTION D.Flashing the Field is the process of applying an external current to a generator's field windings to restore its residual magnetism, enabling it to produce electricity again.
Step-by-step explanation:
The correct method used for restoring generator field residual magnetism is Flashing the Field. This process involves applying a brief external current to the generator's field windings, thereby restoring the residual magnetism needed to produce electricity. It is important because the magnetism can decrease to a point where it is insufficient to generate the required electromagnetic field for power generation when the generator is running. None of the other options listed—Overexcitation, Demagnetization, or Reverse Polarity—are standard methods for restoring residual magnetism in a generator's field.
The method used for restoring generator field residual magnetism is Flashing the Field.
Flashing the Field refers to a technique where a generator is briefly connected to a DC power source to re-establish residual magnetism in the field winding. This is done by passing a brief current through the field winding in the opposite direction to its normal operation.
For example, if a generator has lost its residual magnetism and is not producing any output, it can be connected to a separate DC power source, such as a battery, to restore the magnetic field. Once the magnetic field strength is restored, the generator can operate normally.