The Research On Remanence Measuring Instrument Based Novel DC Method

Electromagnetic current transformer has been widely used in the electric powersystem,as the standard equipment for protection and metering. Since the hysteresischaracteristics of electromagnetic materials, electromagnetic current transformer producesa large amount of residual magnetism after short-circuit fault. Remanence is difficult toeliminate during normal operation, it will seriously affect the transformer transient andsteady state characteristics. Remanence factor as an important parameter of CT is essentialin the design, production and factory inspection for CT. But the country has not beensuccessfully developed measuring instruments to accurately measurement remanencefactor. Therefore, we propose a novel DC method and develop the Remanence MeasuringInstrument.This paper analyzes the characteristics of the traditional DC method and AC method,which requires degaussing before testing.The remanence factor is less than desired resultwhen it degausses defi-ciently.So this paper presents a novel DC method which removesthe demagnetization. It adds the process of reverse charging to current transformersaturation on the basis of traditional DC method.This method measures field current andthe voltage in the secondary side of CT in positive charging process, the discharge processand the reverse charging process. The change of magnetic flux is acquired by integraloperation of the above voltage and current. Then calculates the three data so that obtainthe initial flux and remanence factor of the current transformer.Based on the novel DCmethod, the paper developes a remanence measureming instrument and remanencemeasuringt software in Labview.It analysis the difference of remanence factor between remanence measuringinstrument and CT analyzer of omicron.The instrument eliminates error though therevision for zero drift, sensor errors, data collection point and excitation current. After the revision, it compares remanence factor and saturation flux to the result which wasmeasured by oscilloscope so as to verify the accuracy of the remanence measureminginstrument.The uncertainty analysis of remanence measureming instrument is based on dataacquisition system and measurement software. The uncertainty which includes initialflux,remanence, saturation flux and remanence factor further confirmes the stability andaccuracy of remanence measuring instrument.