The impact of Internet transmission on the uncertainty in the electric power quality estimation by means of a distributed measurement system

There is increasing evidence, in literature, that the estimation of the electric power quality requires the simultaneous measurement of several quantities and indices in all lines connected to the same point of common coupling. The increase in the performance that the measuring systems based on digital signal processing techniques has undergone during recent years and the capability of the digital systems of interconnecting and exchanging data are making these systems more and more appealing and cost-effective for power quality applications. Moreover, the availability of a world-wide, low-cost, and public-domain interconnection system, the Internet, is pushing the evolution of the remote measurement systems, where the measurement results provided by in-field measurement systems are collected and stored by a central unit, toward the distributed measurement systems, where different systems, located in different places, share the same data in order to perform a measurement. It is known that the major drawback of these systems is the lack of synchronization of the shared data, due to the variable and unpredictable throughput of the net, which may affect the uncertainty of the result of the measurement in a quite significant way. This paper analyzes a distributed measurement system for electric power quality measurements and shows how the possible detrimental effects of data transmission over an Internet connection can be reduced by means of a suitable use of averaging techniques, thus avoiding a strict and expensive synchronization between the different units of the distributed measurement system. Finally, an estimate of the effects of the possible transmission delays on the measurement uncertainty is given.