Hi Maya,
As per my understanding, you want to know the reason for the three phase-to-phase voltages being different. The reason behind this outcome is due to the “Solver Type” settings. For a "Variable-step solver", the “auto” solver takes large steps to solve the underlying numerical equations and the resulting output (sinusoidal wave for each phase-to-phase voltage in this case) is not completely accurate. Since the output of the three-phase source voltage is not perfectly sinusoidal, the RMS calculation varies for each of the phases.
Hence it is advised to choose solver type carefully for SimScape blocks as it represents physical simulations. You can read more about the solver selection by referring to the following link:
Upon changing the solver to “Fixed-step” or “daessc" for "Variable-step", you will get the RMS value same for all the phase-to-phase voltage as shown below:
Hope it helps.
