Recent content by Fuselink

So, this means that for SLG fault study I need use double the impedance and for LL faults the 3C model will work right? As I mentioned, transformer secondary is 120/240v. I am not sure if SKM will consider this automatically or I need to pt two cables inseries to double up impedance?

II need to calculate the impedance for 3-1/c #1/0 RW90 wires in steel conduit. This is the secondary of 240V single phase transformer. I have the values for 3-1/c wires and somebody told me that for 2 wire the impedance will double! I can’t find any reference to this to back it up and he says...

ZogZog, 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...

The problem with modeling was that I had to choose YGrd for three phase and then I would get VLN.

Thanks everybody for valuable inputs. 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...

So, based on this all single pole feeder breakers also need to have same rating as the main breaker. because a single phase to ground will pass through them? Sorry, transformer was 37.5 KVA.

BJc, 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...

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...

Thanks for all replies. So the second setting is the margine required between the secondary device and transformer curve damage. What do you mean by true delta-wye? I have heard this before…. Regards,

Then, what this has to do with shifting the xfrm curve to the right. Suppose if my STPU is 2000A I make sure that fuse curve is on the right side of 3400A line.Right?

IEEE 242 requires 15% margin between the main secondary curve characteristics and the primary fuse. I have seen several expressions in different books. For example some books just consider .58% curve shift to the left for transformer damage curve and do not consider L-L faults. Like (SKM...

Utility has provided us with maximum and minimum 3P and L-G short circuit values. Which one of the values id recommended to be used for fuse, Circuit breaker Short circuit rating as well as short circuit study and coordination. This will determine which values to be used in SKM as utility data...

For L-G fault If=3*I0 and I am getting the right answer Ia0=800A Ia0=3*I0=2400 but for L-L-G If=3*I0 is giving me 1763A for L-L-G Ia1=2171A Ia0=588A Sorry, It's been long since I have used these equations.

Sorry about that. Voltage is 44000V.

Dear Friends, I am trying to figure out how hydro has calculated the L-L-G fault based on the following info. My answers do not match. Based on IEEE 80. L-L-G I0=E*X0/( X1*(X0+X2) + X2*X0) ( Page 96) L-G I0=E/(X0+X1+X2) X1=X2 Then I get L-L I0=1763.98 L-G I0=2400.2 Hydro Info...