MATLAB: What algorithm is used to calculate the Transformation Ratio in the Synchronous machine block in SimPowerSystems

Simscape Electrical

I would like to know how the transformation ratio is computed using the nominal field current parameter in synchronous machine block. In the help for any synchronous machine block in SimPowerSystems library, (e.g. Synchronous machine SI Fundamental block), in Fundamental Parameters in SI Units section, there is a parameter named 'Nominal'. For this parameter, it is mentioned that "The nominal field current makes it possible to compute the transformation ratio of the machine, which allows you to apply the field voltage viewed from the rotor, as in real life. "
I want to know the algorithm used to compute this transformation ratio.

Best Answer

This change has been incorporated into the documentation in Release 2011a (R2011a). For previous releases, read below for any additional information:
The transformation ratio (TR) in the Synchronous machine block can be calculated employing the value of the nominal field current as follow:
        TR = (2/3)*(Inom_field/Ibase_stator) .............................(1)
where,
        'Inom_field' is the nominal field current (in the rotor field) 
        'Ibase_stator' is the stator base current.
The stator base current can be expressed as follows:
         Ibase_stator = sqrt(2/3)*(Pbase/Vbase)
where,
         'Pbase' is the base power
         'Vbase' is the base voltage
Please note that the transformation ratio calculated above is the same as given by the following equation:
          TR = (2/3)*(Nf/Ns).............................(2)
where,
         'Nf' is the number of field winding turns
         'Ns' is the number of stator winding turns
Although the latter expression (2) is more common in literature, the two expressions may be shown to be equal empirically.
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