Fault Current Distribution

[charz]

1.Star connected earthed neutral Source to Star connected earthed neutral load? Say if a L-G fault occurs between the source and load, How does the fault current gets distributed? To the source side neutral or load side neutral?
2.Star- Star Transformer. Neutral earthed on both the primary and secondary. say If a L-G fault occurs on secondary side, does the fault current flow in to the primary side neutral too? How does the fault current reflected in the primary?
3. Star- Delta Transformer. Neutral earthed on Star side. say If a L-G fault occurs on Delta side, does the fault current flow in to the star side neutral? How does the fault current reflected in the star side?

 

[xnuke]

Have you tried to draw these situations? The answers should be pretty obvious if you do.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[waross]

Four Wire Wye primary to Delta secondary. A connection to avoid in distribution circuits.
You have not specified a grounding scheme for the delta circuit. There may be no or little fault current with a L-G fault on the delta.
With a Line to Line fault on the delta things get real interesting.
The faulted phase drops to zero Volts and the current is limited by the transformer impedance. (Consider three equal, individual transformers in a bank to make it simpler.)
Now the other two phases form an open delta. This open delta also feeds the line to line fault on the third phase. When the phase angle displacements of the current through the other two transformers is considered, it will be seen that the open delta contributes a fault current equal to the current through the shorted phase.
When a load or a short is placed across any single phase of the delta, the current is equal in all three transformers.
For a load on "A" phase of 100 Amps, the current in the "A" phase transformer will be 50 Amps;
The current in the "B" phase transformer will be 50 Amps;
The current in the "C" phase transformer will be 50 Amps.
The current in one unloaded phase will be at a PF of 50% lagging and in the other unloaded phase the current will be 50% leading.
The current in each primary phase will be 50 Amps divided by the transformer ratio.
I'll let someone else work out the neutral current.

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

 

[dpc]

What do you have so far? A tip: current can't flow in one transformer winding unless it flows in the corresponding winding on the other side of the transformer.

 

[7anoter4]

1)The current will flow through the faulted phase conductor from the source up to the fault point . Here it will split part to the source grounding grid and part to the load grounding grid.
The current part from load grounding grid will flow through to the source through Ground and through neutral conductor.
2) The primary current will rise by induction phenomenon in order to preserve Ip*wp=Is*ws. No galvanic connection.
3) The other two phase secondary windings are capacitive loaded only and then
two corresponding phase primary windings are loaded , the neutral and the grounding will carry part of current. However, these currents are negligible.