Pfeifer, Lars Philipp wrote:
Hello everybody,
I have a question about the usage of the transformer in the branch matrix.
I have been reading the manual a few times and also took many looks in the
example cases.
But I still don’t really understand how I have to fill in the matrix for the
transformer.
My problem is the value of the ratio in the table. As an example: How is the
ratio of 1.03 in the case IEEE24 estimated? If I calculate the currents with
equation 3.1 and 3.2 of the manual I get a very different relation between the
currents compared with the relation of the voltage. Because usually the
relation/ratio should be 230/138=1.6667.
I would be very about some help, maybe I am just thinking in the wrong way.
Best regards
Lars Pfeifer
Lars: the FROM:TO ratio in MATPOWER is
tau * exp(i*theta)
where tau is the _off-nominal_ turns ratio, relative to the _nominal_
turns ratio. If a transformer connects a 230kV bus to a 138 kV bus and
the winding taps are at the nominal position value, then tau=1.0 . A
value of tau=1.03 means that the tap in the primary is at a position
that yields a physical voltage of 1.03*230kV in it should you apply the
nominal 138kV in the secondary.
Remember that the ideal transformer part of a transformer model
"disappears" when you convert the whole network to per-unit. It is only
if the taps are in an off-nominal position that this has to be taken
into account using tau.
carlos.
