Impact Of Harmonics On Current Transformer Characterization And Energy Measurement

Along with the increase in nonlinear load, harmonic content increased obviously inthe grid, harmonic pollution problem is becoming more and more serious. Harmonicdistortion will not only loss the service life of the transformer and cable equipment,make the protection misoperation, interference data communication, etc., will alsoproduce a great impact on the electric energy metering. For electric energy metering,related research focus on the watt-hour meter under the harmonic measurementaccuracy and measurement methods of improvement, often neglected in electric energymetering device and watt-hour meter with the effects of the use of current transformer.In the face of power grid is more and more complex signal, based on the design of thepower frequency current transformer is faced with great challenge. For non-sinusoidalconditions the change characteristics of current transformer, leading to some relevantissues influence on electric energy metering, this paper carried out research, the mainresearch content is as follows:First of all, this paper introduces the working principle of current transformer,based on its equivalent circuit are analyzed in detail the primary and secondaryrelationship between each parameter and the causes of error of current transformer. Bythe phasor diagram and the electromagnetic relationship of contrast of currenttransformer is deduced and the Angle difference expressions, delves into the use errorformula parameters on the effect of current transformer error.Second, summarized the existing model of current transformer, the advantages anddisadvantages of all kinds of model are analyzed in detail. Combined in this paper, theresearch content and characteristics of the model, the selection of the under thecondition of non sinusoidal simulation and actual results are close to J-A and LUCUSmodel, prepared for the next research work.Third, the establishment of a current transformer under dc equivalent analysismodel. Is deduced under the dc component of the current transformer and errorcalculation formula. Through calculation, the dc component of current transformer andvariable error influence is very big. Active power error of fundamental wave to quantifythe dc component and the relationship between the electric energy metering. Toimprove current transformer under dc component in variable transfer some improving Suggestions are put forward.Fourth, in order to reduce spectral leakage in the case of asynchronous sampling,USES the FFT algorithm based on Hanning window function, improve the accuracy ofharmonic analysis. Comparative frequency response method, this paper proposes a newmethod of analyzing the current transformer harmonic transmission characteristics,through the simulation comparison, found that the frequency response method theresults may not be practical and reliable. Impact on the harmonic conditions andvariable current transformer characters made a in-depth study of some of the factors.Fifth, based on the nonlinear current transformer, this paper derived the errorexpression of harmonic active power. Studies have shown that nonlinear phasedifference generated by the current transformer may bring the great influence ofharmonic active power measurement, which affect the electric energy metering. Workenvironment, the conditions of PSCAD simulation current transformer in the circuit ofthe harmonic pollution and simulation analysis was carried out on the actual waverecord data, the simulation results prove the conclusion.