locate the fault point. The most and commonly used technique
to locate fault at transmission line is impedance based
technique [7]. It measures the impedance by dividing the
fundamental frequency of voltage and current phasors at the
relaying point. It is widely used because of its simplicity and
easy to be adapted to electronic devices. However, this
technique is severely affected by fault resistance value where
the inaccuracy of fault location estimation increases with the
increase in fault resistance.
Available impedance based techniques also can be
classified into one-terminal and two-terminal algorithms.
Because of limitation in gaining measurement parameters,
one-terminal algorithm uses many assumptions in fault
location estimation which may lead to inaccurate result. Twoterminal algorithm is more accurate than one terminal
algorithm because it uses the voltage and current
measurements from both substation terminals. The data are
sent using low speed communication channel available at the
substation. This algorithm is expected to replace one-terminal
algorithm in the future because of the increasing use of
intelligent electronic devices (IED).
Two-terminal algorithm as was proposed by the author from
the previous research is used to estimate the fault location [8].
The algorithm does not need source impedance parameters
and estimated fault location is not influenced by fault
resistance value. Equation (1) represents the algorithm for
fault location calculation for Single Line to Ground (SLG)
fault while Fig. 2 shows the SLG fault condition at a phase
line.