Hello,

I am trying to figure out how the star connection works. So far I can't understand how for a 3 phase 3 wire unbalanced load the sum of currents is still equal to zero. And the voltage at the star point is at some voltage value.

Then when a neutral wire is connected the sum of current is no longer equal to zero.

Any help would be very appreciated

cheers

 

Lukee.. . unless the load midpoint is connected to the voltage source neutral, there is no neutral-current.

Furthermore the voltages across each branch of the load will be different, thus exposing one, or two to over-voltage, because of the phenomenon called, "Neutral Displacement." (more aptly called 'centroid' displacement)

Regarding your "Sum-related" question: Yes, But, only if the load-midpoint and supply neutral are connected.

Regards,
Phil Corso

 

yes exactly, the total sum of currents must be zero by Kirchhoff's current law.

So when there is no wire between the load star point and the neutral, the current will be distributed over the loads, thus changing your voltages no?

And also, I had this one "problem" that I just can't understand. where does the neutral wire go to? does it go back to the generator? or perhaps it is passed through the ground?

 

Lukee

Ans to your 1st query:
Yes. Voltages across each load will differ.

Ans to your 2nd query:
Yes. However sum of 3 line-currents will equal zero.

Call the load's midpoint its centroid. Then the voltage between the centroid and system neutral is referred to as displacement voltage. Depending on load parameters, its magnitude will be greater than zero. In fact, it could be dangerously high!

Phil

 

When there is no wire between the load star point and the
neutral, the current will be distributed over the loads dependent on impedance. Voltage drop across each load = IZ

You can only have a neutral wire if the system source has a neutral-point connection. If a particular system has no neutral, one can be derived, typically by using an isolation transformer with either a wye-configured secondary or a center-winding tap.