Abstract:
The main sources of error and other difficulties associated
with the distance protection of dual-circuit transmission
lines are well known. However, the design or selection of protection
schemes usually fails to consider some of the more extraordinary
faults that do occur.
This paper considers the observed impedances that result from
intercircuit faults on a simulated dual-circuit transmission line,
where variations in the phasing as well as the impedance ratios
have been considered. The simulations performed with the Alternative
Transients Program show that intercircuit faults may be undetectable
in the instantaneous protection zone depending on the
scheme adopted and the impedances of the surrounding network.
The observed under-reaching has the potential to lead to a loss
of major loads, maloperation of single-pole tripping schemes and
even system instabilities based on the critical clearance requirements.
