One major advantage of compensated networks is that the rms of the fault current is small so it can be allowed to persist
for several hours. The continuous operation of the system can be sustained during a single-phase to ground fault, in order
to continuously supply the consumers. The residual current at the fault location has to be kept securely below 12 A in order
to ensure, that the touch voltage remains below 65 V during the steady state faulty operation.
A great disadvantage of compensated networks however is the complicated way a single phase to earth fault can be located.
To find it, the first step includes the selection of the faulted feeder. In case of a single phase to ground fault the rms
of the compensated fault current is small, therefore the feeder selection using an overcurrent relay will be unreliable.
The next step is finding the location of the fault along the selected feeder. This is done by first isolating the faulted section using
remote-controlled switch-gear, which involves a number of switching on and tripping sequences– and therefore disturbance
of the consumers – before the faulted section is found.
As there are several time-consuming solutions for determining fault locations and fault resistance, all of them causing consumer
disturbance, we propose a new, effective method, where fault location is performed by injecting current in parallel to the Petersen coil.
The proposed method uses the fundamental component of the zero sequence voltage and the fundamental components of the zero
sequence feeder currents.
The frequency of the injected current is chosen so that it does not coincide with any of the harmonic or ripple control
frequencies that are presentat the network. Hence, this method is independent from the disturbing effects of external
circumstances to a great degree. For the sake of continuous power supply, this method is implemented economically,
employing a simple design, adapted to the substation protection automation system; it is much more accurate than
the previous solutions, employing real-time measurements of relatively short duration.