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 (S3-ø).
-The voltage is the line-to-line voltage (Vline-line)
Current is only defined for a single phase, so in order to determine the single phase current, solve
S1-ø = Vline-nuetral * I (where I = current)
To convert the values the power flow calculates to the ones in this equation, do the following
S1-ø = S3-ø / 3
Vline-nuetral = Vline-line / sqrt(3)
Thus we can write
S3-ø / 3 = Vline-line / sqrt(3) * I
Which simplifies to the equation used to determine the current on a transmission line
I = S3-ø / ( sqrt(3)* Vline-line )
Note: The same equation is true for a transformer.
July 5, 2012