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I have balanced star three phase generator 380V with junction point is connected to ground And current through from junction point to ground is I0=0 for that clearly say it is balanced system when i cut off junction point from grounding that apear 30V in junction point Why that voltage appear? Through it is balanced??

It may question for power engineeringenter image description here

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    \$\begingroup\$ The generator alone is 'a balanced system', but how about the meter? And the excitation for the generator? \$\endgroup\$ – Whit3rd Dec 22 '17 at 8:43
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The diagram shows a 208V system, not 380V.

Nothing is perfectly balanced. There is some small imbalance in the transformer windings and the primary voltage. There is also some capacitive coupling between the transformer primary and secondary. A high-impedance meter will always show some small voltage that will disappear with a little less impedance to ground.

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As Charles Cowie says, there is no perfect world, I mean the system cannot be 100% balanced.

Since you are measuring the floating star point, then the only path to the ground is through leaking capacitance. The measured voltage is only due to the different capicatitance of windings regard to the earth.

Also the statement that if you connect the star point to the earth and the current iz zero this means that you have a balanced system is wrong. It would be true if the generator is attached to balanced load and only then if the current is zero, you have a perfect balanced system gen + load.

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