Evaluation of the Electricity Metering Accuracy by Commercial Accounting Unit

Abstract

The method for evaluation of the electricity metering accuracy by a three-phase commercial accounting unit in a reduced load mode is proposed. The method enables to determine the incomplete calculating of electricity by one or several phases in the case of a decrease in the load level of current transformers to values at which the permissible error is not standardized for a given accuracy class, or the operation of the electric energy meter of a transformer connection is in the dead mode. This is typical during downtime of production equipment at night, on weekends and holidays, when only the territory lighting of the enterprise, video surveillance, burglar alarms etc. are functioning. The method makes it possible to evaluate the relationship between the measured value and the phase currents using a fuzzy function. The measured value is the relative deviation of the readings of the transformer connection meter from the actual energy values, which are estimated from the readings of the direct connection meter. To estimate the parameters of the approximating dependences for the boundary real functions, which determine such a fuzzy function, it is necessary: to obtain samples of the measured value for each measuring channel when the current of the corresponding phase changes within the limits that correspond to the reduced load mode; for each of the samples, using the theory of fuzzy sets, estimate the boundaries of fuzzy intervals characterizing the measurement result; the boundaries of the obtained fuzzy intervals for fixed values of currents of a certain phase are approximated by functions representing the sum of two exponentials, as a result of which fuzzy functions are obtained that characterize the accounting uncertainty for each phase; estimate the boundaries of the desired fuzzy function, which determines the uncertainty in the measurement of electricity in three phases, as the root of the sum of the corresponding boundaries squares of the fuzzy functions, which show the accounting uncertainties for each phase. It was found that in the reduced load mode the incomplete counting of active energy over one measuring channel of the transformer connection meter of accuracy class 0.5 S can reach 3 %. The use of the method will make it possible to improve the accuracy of financial calculations between suppliers and consumers of electricity.