Refinement of the mathematical model of electrical energy measurement uncertainty in reduced load mode

Abstract

The object of the study is a three-phase commercial electricity metering unit for 380 V electrical grids. The uncertainty of electricity measurement in the reduced load mode is estimated by the relative deviation of the active energy, measured by the metering unit, from the actual value. The specified deviation is considered as the value of relative deviations on measuring channels, weighted by phase currents. The method of estimating the uncertainty of electricity measurement by one channel of the metering unit is based on the approach to estimating non-random uncertainty using the fuzzy set theory. The parameters of membership functions for the relative deviation of the metering unit readings are estimated at fixed levels of the channel current. Approximation of such functions for different current levels allows you to obtain a set of boundaries of the L-R type fuzzy function corresponding to a set of confidence levels. This allows determining the impact of the load phase current on the measurement uncertainty if the amount of empirical data is limited. The mathematical model for estimating the uncertainty of electricity measurement at reduced load using a fuzzy function was refined. The proposed model differs from the known ones by taking into account the influence of load values for each phase of the metering unit on the measurement uncertainty indicators. The method for determining the membership function and the marginal confidence level, which characterize the uncertainty of energy metering by the metering unit, is proposed. The mathematical modeling results are confirmed as adequate to the experimental data. The proposed model for estimating the measurement uncertainty allows estimating the level of underestimation and clarifying financial calculations between the seller and the buyer of electricity.