Thanks all of you for your suggestions. From the discussion what I
have understood is that the potential of any point to the earth
depends upon the charge of the point, distance of the point from the
ground (ground capacitance!!).
Thus to evaluate the potential difference (p.d.) between the floating
star point and the ground we must be able to evaluate the charge of
the star point. DK described that the p.d. depends on the ground
capacitance, overhead cloud. This is because it affects the charge of
the star point, am I right DK? But I still don’t know how to evaluate
When the star point is connected to the earth, we are simply putting a
conductor between two plates of the capacitor i.e. earth and the star
point which makes the p.d between them zero and all the charge at star
point will be drained to the earth.
Pls give ur suggestions.
Not all potentials to earth are due to static or quasi-static charge
sources. For such cases, you are right in considering a capacitive coupling.
Such potentials will not be related to the generated voltage. No- you can't
evaluate the charge because you don't know the conditions.
Also mentioned were more mundane things such as unknown and unbalanced
leakage paths, unbalanced loads to ground, and the worst is a fault to
ground somewhere in one of the windings. so that the star point to ground
voltage could lie between 0 and phase voltage. In the latter case,
connecting the star point to ground might do serious damage.
Since you have given no information, and apparently have done no tests, it
is difficult to give you a meaningful answer for your situation.
For example, is the voltage there when the generator is not running? If not-
forget the cloud charges. Is it there when the generator is unloaded? Can
you measure resistance between the star point and ground (generator not
running)? There are things that you can do to narrow it down if it is a
So, my suggestion is that you should get a local professional consultant to
examine the situation rather than hope to get free long distance advice
Don Kelly email@example.com
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