How does Simulator convert transmission line flow between MVA and Amps?

Variables that are calculated by a power flow are the MVA flow leaving a bus along a transmission line and the bus voltage.

-The MVA flow is the total MVA flow on all three phases of the transmission line (S_3-ø).
-The voltage is the line-to-line voltage (V_line-line)

Current is only defined for a single phase, so in order to determine the single phase current, solve

S_1-ø = V_line-nuetral * I (where I = current)

To convert the values the power flow calculates to the ones in this equation, do the following

S_1-ø = S_3-ø / 3
V_line-nuetral = V_line-_line/ sqrt(3)

Thus we can write

S_3-ø / 3 = V_line-line / sqrt(3) * I

Which simplifies to the equation used to determine the current on a transmission line

I = S_3-ø/ ( sqrt(3)* V_line-line )

Note: The same equation is true for a transformer.

July 5, 2012