Determining the static characteristic of a measuring current transformer at a reduced load of the metering unit

Abstract

The object of the research is a measuring current transformer of the electromagnetic type, which is used as part of the electricity metering unit. The current transformers functioning in the mode of reduced primary current is accompanied by significant errors. The existence of such a regime for a long time due to downtime of production equipment leads to a significant underestimation of electricity. This leads to unjustified financial losses for energy supply companies as electricity in many countries has become more expensive. The static characteristic of the measuring current transformer at a reduced load of the metering unit is described by a linear statistical model. The parameters of the model are estimated on the basis of empirical data using methods of covariance analysis. The adequacy of the model is confirmed by analysis of regression residuals. The obtained statistical model of the static characteristic, unlike the known ones, is characterized by universality, as it describes current transformers with an arbitrary transformation ratio within the studied accuracy class of 0.5S. The uncertainty of the current error is estimated using the prediction intervals for the transformers secondary currents as a function of the primary currents, calculated on the basis of the obtained model. The prediction intervals for sample values of the current error were obtained through the application of the proposed approach for uncertainty estimation of such an error at a reduced load of the metering unit. It was found that the current error can reach −20 %. Taking into account the indicated intervals for measuring current transformers at a reduced load of the metering unit during billing will allow energy supply companies to increase the accuracy of commercial electricity metering.