Pole mount xfmr
Pole mount xfmr
(OP)
Dear Friend,
I have a 45KVA pole mounted single phase transformer (7300V to 204/120V) which feeds two distribution panel, through 3C/1/0 cables in 2” conduit. I need to calculate short circuit current at the panel.
What I don’t have is the xfmr impedance and impedances on the wire.Could you please refer me to a source that I can get this info. It’s been long since I have dealt with this stuff
I have a 45KVA pole mounted single phase transformer (7300V to 204/120V) which feeds two distribution panel, through 3C/1/0 cables in 2” conduit. I need to calculate short circuit current at the panel.
What I don’t have is the xfmr impedance and impedances on the wire.Could you please refer me to a source that I can get this info. It’s been long since I have dealt with this stuff






RE: Pole mount xfmr
You'll find approximate value in here. Watch out for the 120/240V three-wire systems. The 120 V fault current will be higher than the 240 V fault current, at least close to the transformer.
RE: Pole mount xfmr
http://w
RE: Pole mount xfmr
The service length shows the secondary wiring right?
Does this mean if I were to use a panel with main breaker at 240V , 10 feet away from transformer , then I need to have a main breaker with SCCR greater than 10423 A and also all single pole breakers need to be rated greater than 17119A?
feet 240V 120V
0 11161 22323
10 10423 17119
Thanks for the reply
RE: Pole mount xfmr
RE: Pole mount xfmr
Those numbers are for a 37.5 KVA ( 45 KVA are not a standard size for pole mounted xfmrs.
You should use a 50 KVA and be more realalistic about the distance. The transformer is going to be at least 20' up the pole.
That should put you below 10 KA, 22 KAIC panels are pretty common if you'r not sure buy 22 KAIC.
RE: Pole mount xfmr
Sorry, transformer was 37.5 KVA.
RE: Pole mount xfmr
RE: Pole mount xfmr
For an analysis of short circuit currents in single-phase transformer, see Conrad St. Pierre's book "A Practical Guide to Short Circuit Calculations."
RE: Pole mount xfmr
See the enclose link with information from different sources.
http:
http
RE: Pole mount xfmr
RE: Pole mount xfmr
A Kuhlman 37.5 KVA pole mount single phase transformer, 7620 x 120/240 has an impedance of 1.7%. This should be similar for other manufacturers of like transformers.
One note this is an oil filled transformer, not a dry type and the rating is taken at 85 deg C. Also this transformer has core loss of 106 watts and load loss of 410 watts.
This information comes from Kuhlman test data.
Hopes this helps
RE: Pole mount xfmr
Transformer is from “ Can Tran Co”. Unfortunately, design impedance is not shown. It says” Tested % impedance to be entered “ . SKM shows 3.5% which to me is high for this type of transformer.
Transformer is 8320 GrdY/4800 . I am not sure if I can model this using single phase module in SKM. Because it’s asking for VLL and H2 is grounded in transformer.
RE: Pole mount xfmr
RE: Pole mount xfmr
Utility is not that cooperative in this regard. On the other hand, I can see that level of SC MVA will affect fault currents substantially.
SKM requires three phase MVA and Line-ground utility contribution data. Since, I am dealing with single phase scenario, how three phase contribution can affect the calculation. As I mentioned, H@ is grounded and therefore, I only have MVA contribution from utility on one phase.
RE: Pole mount xfmr
However, the good news is that this is taken into consideration in the ratings and acceptance tests of panels and breakers.
For instance a breaker rated for 10,000 amps RMS will safely interupt the worst case current from a transformer with an available fault current of 10,000 amps or less.
Consideration of the reactance of the feeder cables will often drop the available fault current down to a lower rating class.
respectfully