I have a doubt on above question. Suppose in normal earthing system take star connection (440V) as power source and its neutral is earthed, when we check voltage between a phase and earth we can see around 250V. But in insulated neutral earthing system using in ships, how much voltage would be present? take source as 3 phase 440V star connection.

 

An insulated power system will always have a voltage between all connections an ground this is due to internal capacitors of the separating transformers. ( assuming a connection to shore). The current ( micro or mA) are important and depends from the way the transformers are build.
I do understand that you do not want a current running from ships hull to ground.
It is difficult to give an answer without proper measurement (done at location).

Picbuster

 

An insulated power system will always have a voltage between all connections an ground this is due to internal capacitors of the separating transformers. ( assuming a connection to shore). The current ( micro or mA) are important and depends from the way the transformers are build.
I do understand that you do not want a current running from ships hull to ground.
It is difficult to give an answer without proper measurement (done at location).

Picbuster

does it shows zero voltage? because the alternator neutral point is not grounded alsr it shows some value?

 

does it shows zero voltage? because the alternator neutral point is not grounded alsr it shows some value?

There normally is a high value of voltage to ground but not much current capability (high impedance) due to stray capacitance and leakage. We normally had a set of neon bulbs on each phase to ground to indicate if there was a short (lamp would not be lit) on the ships internal power feed to equipment. All ac distribution systems on U.S. Navy ships are ungrounded.

 

In average european grid 380/220 we have few volts between gnd and earth, except accident situations when it may go up to 12 or even 15 volts. Normally the 4 Ohm resistance must be obeyed everywhere surplus the wire impedances, so the disbalance may cause indeed not so big trouble. However I survived the accident where at our house was rusted away those surplus wire what was dug at early after WW2 times, providing the zero. Then some inhabitants received so much as 420V, wilst others just 80V. Quess who was most claiming afterward.