Line monitoring and fault location using spread spectrum on power line carrier

Signals transmitted over the power line carrier system are used to locate faults and other impedance mismatches on EHV power lines. The compatibility and sensitivity performance requirements for doing this are summarised. Conventional remote sensing waveshapes are reviewed and direct-sequence spread-spectrum modulation is proposed for this application. Optimal signal processing techniques are outlined and frequency domain correlation techniques are detailed. Prototype hardware has been constructed and on-line results are presented for a 225 km 330 kV line. Line reflections were identified within an accuracy of 1.6 km even though the channel bandwidth was limited to 50 kHz by external constraints. It is shown that accuracy is dependent on channel bandwidth, signal-to-noise ratio and waveform energy. It is suggested that a further increase in accuracy is possible by referencing the received signal to known impedance discontinuities such as the transpositions. Fault location accuracy down to one span should be possible using this technique, which will work on both energised and de-energised lines.