Hi,

is anyone here who is really into the stuff of electrical machines? It is a question that deals with detailed electrical engineering:

I don´t understand the model of the synchronous machine (electrical excited) especially the TurnsRatio for the excitation current.

TurnsRatio=sqrt(2)*VNominal/(2*pi*fNominal*Lmd*Ie0).

Why is only Lmd taken into account? IMHO the idle current is calculated but then I would expect the stray inductance and the stator resistance to be also taken into account.

So my suggestion is:
TurnsRatio=sqrt(2)*VNominal/(sqrt[(2*pi*fNominal*(Lmd+Ldsigma))^2 + R1^2]*Ie0).

Who can help me?

Thanks.

Hello RungeZipper,

the answer is quite simple. The TurnsRatio gives you the transformation rate of the rotor in respect to the stator. Stray-inductances and resistances don't contribute to this transformation rate. They "just" cause losses. But you are probably with me that losses on the stator side won't be transformed to the rotor and vice versa. The only inductance which transforms the currents and voltages is the mutual inductance Lmd.
Another way to explain it is that to measure the TurnsRatio the stator side would be open circuited. Thus no current would flow and thus no losses in the resistances and stray-inductances.

Dietmar

Thanks for your reply.

OK, at the moment I´m reading books about electrical machines and I´m trying to find the analogies between the theorectical equations and the models in Modelica. I´m still not with you although I understand the explanation itself. The calculated current VNominal/(2*pi*fNominal*Lmd) does not have any physical meaning. Am I right?

The main problem I have is to understand the transformation of th DC excitation current into the threephase (or into the space phasor) equation system. On the one hand you have to be carefull because of the factor sqrt(2) that is between a DC and an AC magnetic field. Considering a threephase rotating field the factor 2/3 also must be multiplied. And in addition to that you have the different stator and rotor windings that are taken into account. Which of these 3 phenomenons are included in the TurnsRatio? What we were talking about before is the number of windings. OK. Then the factor sqrt(2) is also included. But that would be the translation for an AC field and not for a rotating field caused by a threephase current.

The key for me seems to be the Potier triangle which is mentioned in many books. That´s the solution to calculate the real excitation current in dependency on a choosen stator voltage and current. The idle current line is inlcuded there. That is why I first thought of this line beeing also calculated in Modelica.