Load sharing in GrdY 3 PH banks 2

[ffont]

Looking at the ABB Distribution Guide page 63 and 64 and applying it to a GrdY-GrdY bank, it appears that a balanced three phase load will split evenly between the 3 phases. Am I correct in assuming that the currents in each phase will be different and proportional to the Iz of the individual leg (more precisely the voltage regulation).

Would the same apply to a single phase load connected line to line? ie that for a 100A load current the split will not be 57.7A in each of the 2 legs

The voltage unbalance will just be reflected by a higher zero sequence current flowing in the neutral?

 

[waross]

No,
No,
and
No.
The impedance of the load more than an order of magnitude greater than the transformer impedance and may be several orders of magnitude greater than the impedance of the transformer. The load impedance will predominate in determining the current.

Given a 100 amp line to line load, the current in each line will be 100Amps.


"The voltage unbalance will just be reflected by a higher zero sequence current flowing in the neutral?"
Confusion reigns.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[magoo2]

I guess I agree with Bill. Unless you have a load greater than the transformer rating, in general, the load current will be determined by the load impedance.

The individual impedances of single-phase transformers will have some effect but it won't be than significant. The phases with higher impedance transformers will have higher voltage at the load (with respect to grond) than the phases with lower impedance transformers.

If you have some difference in the three voltages at the load, then you will have some difference in the phase currents. With unbalanced currents at the transformer neutral, you'll develop some neutral to ground currents.

If you model this with symmetrical components, the motor will change the amount of unbalance but you'll still get zero sequence current flow to ground.