I have small observation for 3 Phase system. First observation-
1) When 3 Phase AC Source was balanced
a) L1-N=230VAC
b) L2-N=230VAC
c) L3-N=230VAC
i checked voltage between Neutral and PE (Protective Earth) and found it 0.023V
Next observation-
1) When 3 Phase AC Source was imbalanced
a) L1-N=230VAC
b) L2-N=230VAC
c) L3-N=0VAC
i checked voltage between Neutral and PE (Protective Earth) and found it 70V
Now i could not able to differentiate why this is happened.
Can someone help me with mathematical calculations how to find Neutral to PE (Protective Earth)?
It is impossible to calculate. As Klaus pointed out, the measurement depends on the exact circuit details. In theory, PE and Neutral are different circuits so any potential is possible.
If PE and Neutral were joined together, which is a common scenario, there would always be zero between them, excepting some small amount due to wire resistance, inductance and capacitive coupling.