  Accurate knowledge of transmission line (TL) impedance parameters helps to
improve accuracy in relay settings and power flow modeling. To improve TL
parameter estimates, various algorithms have been proposed in the past to
identify TL parameters based on measurements from Phasor Measurement Units
(PMUs). These methods are based on the positive sequence TL models and can
generate accurate positive sequence impedance parameters for a fully-transposed
TL when measurement noise is absent; however these methods may generate
erroneous parameters when the TLs are not fully transposed or when measurement
noise is present. PMU field-measure data are often corrupted with noise and
this noise is problematic for all parameter identification algorithms,
particularly so when applied to short transmission lines. This paper analyzes
the limitations of the positive sequence TL model when used for parameter
estimation of TLs that are untransposed and proposes a novel method using
linear estimation theory to identify TL parameters more reliably. This method
can be used for the most general case: short or long lines that are fully
transposed or untransposed and have balanced or unbalance loads. Besides the
positive or negative sequence impedance parameters, the proposed method can
also be used to estimate the zero sequence parameters and the mutual impedances
between different sequences. This paper also examines the influence of noise in
the PMU data on the calculation of TL parameters. Several case studies are
conducted based on simulated data from ATP to validate the effectiveness of the
new method. Through comparison of the results generated by this novel method
and several other methods, the effectiveness of the proposed approach is
demonstrated.
