Fault current
Fault current
(OP)
Is there anyway to calculate by how much fault current increases with a Yd11 vs a Dyn11 132-33kv transformer on the primary side duding a 132kv fault?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
Download nowINTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: Fault current
RE: Fault current
RE: Fault current
RE: Fault current
Is there any special reason to change a Dyn11 with a Yd11 ?
RE: Fault current
Have I been mistaken?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Fault current
I think you are looking for the increase in ground fault current happens when the transformer is YNd11 (solidly grounded WYE on 132kV Utility side). During a ground fault on 132kV side, in addition to the ground fault contribution from the Utility side, there will be a a zero seq current contribution from the primary of the transformer too. Therefore the actual ground fault current at the fault location is higher. But this will not happen if the transformer is Dyn11 because the DELTA winding is not a zero seq source. One thing important here is that if the transformer is YNd11 then during such a ground fault on 138kV side the Utility current contribution becomes little lower. (If you model and calculate you will find this) Depending on the ground fault pick-up setting this lower fault current may not trip the Utility upstream bkr. Therefore, Utility has to adjust 50/51G accordingly. Is this the answer you are looking for or otherwise?
RE: Fault current
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Fault current
This is exactly my concern. The transformer being considered is wye grounded on the primary, and being a zero sequnce source I am not sure how this will effect a single phase to ground fault on the 132kv side or on the 132kv line going into the substation.
Also, what do you mean regarding the utility fault current contribution being lower?
RE: Fault current
The wye point will shift as the voltage on one phase collapses due to the line to ground fault.
If the wye point of the wye/delta transformer is grounded, there will be a contribution or a back feed into a line to ground fault.
The steady state current will be limited by an impedance equal to three times the transformer bank impedance.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Fault current
#2 make sense as a good rule of thumb, I will look in to that.
In regard to this, can has anyone heard of on-board tap changers on a delta-delta transformer? If fault currents are to great of a concern that might be considered.
RE: Fault current
As mentioned before, when there is a ground fault on the 132kV WYE-GND side, there are two zero seq current contributions. One from Utility side and the other from the YNd11 transformer.
If you do a simple model, you will find that Utility ground fault current contribution is bit lower comparing to the ground fault current contribution, if the same transformer is connected as Dyn11 mode. You have to do a calculation or a small modeling to prove this.