Upstream power line communication over distribution transformers for automatic meter reading

Power line communication systems for automatic electricity meter reading which use signals capable of passing through the distribution transformer are attractive because the whole communication channel is utility owned and pre-exists. The performance of current commercial systems is limited to data rates of a few hundred bits per second (bps) which is insufficient for reading interval meters. This thesis addresses the question of whether or not this channel could be used for interval meters. Channel sounding equipment was developed to measure the upstream current transfer ratio and the design of this reliable and portable equipment is presented. It was used to sound six very different channels within La Trobe University's distribution system. The measurements are presented along with the derivation of parametric models of the channels. It is shown that all of the cannels can be represented by one generic type model which is a non-minimum phase system with six zeros and five poles, one of the zeros and one of the poles being fixed and the others varying over limited frequency and damping factor ranges according to the particular channel characteristics. Noise measurements on the medium voltage supply were conducted. These measurements were made in narrow bands across the spectrum of interest. It was shown that, irrespective of the nature of the probability distribution of the wideband noise, measurements within narrow enough bands have close to Gaussian distribution. A method for generating current signals within a meter was demonstrated and an achievable current signal level estimated. This, in combination with the channel models and the noise measurements enabled determination of the Shannon capacity limits for each of the channels. All channels exhibited Shannon limits above 10,000 bps with three of the six channels above 30,000 bps. The implication of this finding is that the channel is suitable for remotely reading interval meters. The thesis is a case study with the assumption is that the la Trobe distribution system is a good representation of utility owned systems but tests to confirm this assumption have not yet been performed. Design of a complete communication system to use the channel for automatic meter reading was not attempted; however, a resonant circuit switched across the mains for meter endpoint signal generation was suggested. Operation of such a transmitter was studied in some detail and the new understanding, missing from existing literature, is presented.

This thesis contained third party copyright material which has been removed pending the receipt of written permission(s). The author was contacted 2011/04/12.