Ripple signal amplification in distribution systems: a case study

Use of high frequency ripple signals for the control of loads such as off-peak hot water systems and street lighting systems is common within distribution utilities. Although injected signal levels are small and within stipulated limits, in distribution systems dominated by underground cables the signal levels received at the load ends can be relatively large due to resonance. One significant problem associated with the excessive signal levels is racing digital clocks caused by the additional zero crossings of the mains waveform. This paper presents the results from a detailed modelling study undertaken on a 22 kV system. The dependency of the results on LV aggregate load models used and the damping provided by the lines and loads are discussed. Mitigation techniques suggested to control excessive signal levels are also investigated.