Fault current through neutral

[Cerkit]

Hi,

Please can someone comment on if a single-phase to earth fault indicated in the diagram will result in fault current returning through the neutral of Transformer 2?

Thanks

 

[waross]

Is T2 a grounded wye secondary?
Is T3 a zig-zag grounding transformer?
If T2 is a grounded wye then T3 may be a waste of time expense and space. It will not reduce the fault current. Acting in parallel with the ground connection to the wye point of T2, T3 may increase the fault current very slightly.
The fault current will return via the ground link to the wye point of T2. If you call the wye point the neutral of T2 then the answer is yes, the fault current will return through the neutral of T2.


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

 

[Cerkit]

Hi,

Yes T2 is a grounded Y secondary.
T3 is a zigzag grounding transformer.

If I fit a residual current relay to the wye point of T2 it should operate for the fault indicated yes?

Thank you for the comments.

 

[waross]

I remember an installation of three flood pumps.
In the switch-gear, each pump starter had an artificial neutral.
The switch-gear had ground detection voltmeters installed, presumambly to detect the failure of an artificial neutral coincident with a ground fault.
The switch-gear had ground detection lamps installed, presumambly to detect the failure of a ground detection voltmeter, coincident with a ground fault.
All this on a solidly grounded wye system.
I wonder if this team has moved on to superfluous zig-zag transformers.

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

 

[Kiribanda]

Cerkit,
I am confused here little bit. You say that T2 neutral is grounded.
But per SLD, your network is again grounded using a Zy grounding transformer (T3).
For me those two are contradictory. Because if the Neutral is grounded in T2,
then there is no need of another grounding transformer (T3).
Is your given SLD correct?

 

[7anoter4]

If your SLD is correct-as Kiribanda asked-then this could be the ground fault current way.
Usually Zig-zag transformer consisted on one three phase winding only and is connected with no neutral grounded systems. See-for instance:

UNDERSTANDING ZIG-ZAG GROUNDING BANKS by JOHN R BOYLE, PSA

https://www.l-3.com/wp-content/uploads/2014/04/Georgia-Tech-Zig-Zag-Grounding-Transformers.pdf

 

[waross]

The ground on T2 effectively shorts out the zig-zag and the current limiting resistor.

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

 

[Cerkit]

Hi,

Apologies, my mistake, as you correctly picked up, T2 is in fact a Star-Delta with the Star neutral earthed, please see revised diagram.

Under this scenario my understanding is that there will be no fault current in the neutral of T2 for the fault indicated as the zero sequence network would terminate at the reference bar after T2.

Do you agree?

Thanks