Research On Nonlinear Characteristics Of Current Transformer And Impact On Energy Metering

With the vigorous development of the power system and smart grid, energymetering is refered to new heights. Energy metering is power information settlementmeans among power generation、power supply enterprise and power user, its accuracy isdirectly related to the interests of the three, it is also the key to development of smartgrid. In modern energy metering system, it is difficulty to improve the measurementaccuracy though inproving measurement algorithm because of the development of themeasurement algorithm. At the same time, measurement error brought by the deviceerror can not be ignored. Actualy, the main device error of energy metering system isTA’s error, The previous studies are lack of TA’s nonlinear characteristic which containsfrequency characteristic, and the energy metering error brought by the TA is not clear.The paper analyzs TA’s nonlinear characteristic and infuention of externalmagnetic field on operating condition on the basis of TA’s erroe theory, quantify theimpact of the nonlinear characteristics of the TA to energy metering.First of all, the paper anlyzs TA’s erroe theory base on TA’s fundamental, andstudies TA phase characteristics under non-periodic component situation, The researchresult reveals that TA’s phase error will increase with the increasing of non-periodiccomponent. When TA is transient saturated, phase error increased sharply, at last, errorsTableilized at a level of limit when TA is deeply saturated.Secondly, derivating the frequency characteristic relationship base on the TA’sequivalent circuit, and study the frequency characteristic of actual used miniaturecurrent transformer though theory and experiment, obtaining a uniform conclusions, it’sthat there is large error at low-frequency, when frequency is between50Hz-300Hz, TAhas good linearity, error will increase when frequency is greater than300Hz. Gevingadvise to improve the frequency characteristic and widen the band of TA. At the basis offrequency characteristic, analyzing the power’s error change with frequency, it revealsthat power’s error change with frequency is similar to amplitude; at the same time, thepapaer analyzed harmonic energy of a manufactory, the result shows that harmonicenergy will reduce if there is a TA.At last, Alayzing the relative position between TA and permanent magnet whenthere is external magnetic field, deducing the quantitative relationship of externalconstant magnetic field impact on the transfer characteristics of TA, verifing the relationship though theoretically and experimentally, studing the infuence to the energymetering. The research result reveals that there is some similarity between externalconstant magnetic field and DC bias impact on the transfer characteristics of TA, andwith increasing of external magnetic induction, the TA ’s transfer error increases, at thesame time produce a large number of harmonics in output signal, seriously affect theenergy measurement results.