
53Theory of Distributed-Parameter Circuits and Impedance
where
Y
s
= Z
s
−1
Y
r
= Z
r
−1
The Z- and Y-parameter methods are stable for θ → ∞ since it is based
on the convergence functions coth(θ) and cosech(θ). Thus, the method is
suitable for transient analysis. However, it should not be used for analyzing
low-frequency phenomena since cosech(θ) becomes innite for θ → 0, that is,
ω → 0.
1.4.4 Modal Distribution of Multiphase Voltages and Currents
1.4.4.1 Transformation Matrix
When a three-phase transmission line is completely transposed or the
impedance and admittance matrices are completely symmetrical, the follow-
ing transformation matrices are widel ...