Method and apparatus for demagnetizing generator components prior to electromagnetic core imperfection testing or EL-CID testing

An apparatus comprising:

• one or more conductors configured for extending through a generator stator core;
• a power supply for supplying a polarity-reversing voltage to the one or more conductors;
• and
• wherein the power supply is controllable to reduce an amplitude of the voltage with time, wherein the voltage causes current to flow in the conductor, the current's magnetic induction acting to demagnetize the stator core.

A method comprising:

• demagnetizing the stator core by:
• extending one or more conductors through or proximate the stator core;
• applying a polarity-reversing first voltage to the one or more conductors;
• and
• reducing an amplitude of the first voltage over time, wherein the first voltage causes current to flow in the one or more conductors, the current generating a magnetic field that demagnetizes the core;
• supplying a second voltage to an excitation current loop;
• and
• passing a detector coil proximate an inner surface of the stator core to determine a magnetic flux produced in the stator core by the second voltage and to detect where the magnetic flux is influenced by hot spots in the stator core.

A method comprising:

• calculating an expected value of current to flow in an excitation loop to generate a predetermined magnetic flux in a stator core;
• applying a first voltage to the excitation loop to cause the expected value of current to flow in the excitation loop;
• measuring an actual value of current flowing in the excitation loop;
• comparing the expected value of current and the actual value of current;
• and
• determining the presence of residual magnetic flux in the stator core from the step of comparing when the actual value of current is greater than the expected value of current.