ETAP Power Grid Modeling help

[kjjack]

I am unsure how to enter this utility information (below)correctly within ETAP v6. Can someone please advise? ETAP asks for percent R and X, but I have what is shown below. Also, would I enter it as 13.2kv or 480V? Thanks



"This location is served from XXXX substation via 13.2 kV Feeder 158 and a 75 kVA bank of transformers (13.2 kV/480 volts). Based on a transformer impedance value of 2.10% and the existing high-side driving point impedance, the available 3 phase (3Ø If) fault current at this location should not exceed approximately 3,890 amps and the available Line to Ground (L-G If) should not exceed approximately 3,950 amps. Both values were calculated at the 480 volt transformer low side bushings and do not include the impedance contributions of the secondary cable.

The driving point impedances on a 100MVA base at the low side bushing are:

Z1 = 6.890 R + j 30.173 X

Z0 = 7.395 R + j 28.556 X

 

[davidbeach]

I've not used ETAP, so I can't talk to it specifically, but you have the 480V per unit impedance on a 100MVA base. If you can get that level of detail from your utility count your self lucky. If ETAP is worth its price, you can enter those values directly.

 

[LionelHutz]

That data is what E-tap is expecting. Enter that data on the short circuit tab. Use Z1 for the positive and negative data and Z0 for the zero data.

 

[vandal06]

I'm running a newer version of ETAP than you are (7.5.0) and I'm able to enter utility short circuit data as either %R+j%X, or short circuit MVA/short circuit kA with an X/R ratio.

 

[kjjack]

vandal06,
would what I have shown, Z1 = 6.890 R + j 30.173 X, be considered as %R+j%X, or do I need to convert it?

 

[vandal06]

My gut tells me it's in percent. Easiest way to check it (without calculating the per unit impedance from the short circuit current given) is put it in the utility model one way and run a fault and see if the result is what you would expect.

 

[vandal06]

Correction: it's in per-unit and would need to be multiplied by 100 to get it in percent. I went ahead and checked it out on my copy of ETAP.

 

[LionelHutz]

Agreed, you multiply the Z1 and Z0 valies by 100 before entering them and then the short circuit kA equals the data you provided.

Another oddity of E-tap. There is a spot for entering the PU data but why ask for it in % and require the user to multiply by 100? It's been a few months so I forgot about that in my last post. If you forget, the short circuit currents are unrealistically high.