As stated in the documentation of the "distributed parameter line" block: "This model does not represent accurately the frequency dependence of RLC parameters of real power lines. Indeed, because of the skin effects in the conductors and ground, the R and L matrices exhibit strong frequency dependence, causing an attenuation of the high frequencies."
Is there a third party model of transmission line, compatible with SimPowerSystems, dealing with skin effect and other nonlinear behavior?