1. A generator neutral ground monitoring device, said device comprising: a direct current (DC) sensor placed on a stator neutral ground lead of a generator, said DC sensor measuring a direct current component of a generator neutral ground current and providing a DC neutral ground signal; an operating environment data module which provides generator operating environment data, where the operating environment data includes generator operating condition data and ambient condition data; and a monitor module including a processor and a memory, said monitor module being configured to receive the DC neutral ground signal and the operating environment data, analyze the DC neutral ground signal in consideration of the operating environment data to detect and predict faults in the generator, and issue an alarm or a diagnostic message if a fault is detected, wherein the monitor module also receives an AC neutral ground signal that includes a DC component, either from the DC sensor or from another sensor capable of reading the DC component, converts the AC neutral ground signal to a frequency spectrum via a Fourier Transform (FT), and uses a zero hertz component of output from the FT as a supplemental indicator of generator neutral ground direct current flow to compare to the DC neutral ground signal.