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Precision AC Current Measurement Technique

Guildline Instruments Limited1PresentationPresenter, AuthorRichard Timmons, P.Eng., MScPresident, Guildline InstrumentsAcknowledgementsTom Barczyk, McSEER&D Product Manager, Power InstrumentsGuildline InstrumentsDr. Petar MiljanicOverviewIntroductionCurrent TransformerMeasurement ResultsStationary SignalsQuasi-Stationary SignalsApplications and ConclusionNeed for More Accurate Power MeasurementsHigher Electricity CostsDemand for Better EfficiencyGovernment MandatedMeasure Quasi-Stationary SignalsGrids are More NoisyMultiple, Alternate Energy SourcesSmart, Unpredictable LoadsIntroductionCurrent TransformerGuildline Instruments Limited5Current Transformer Circuit

Modified DesignError Correcting CircuitNI Primary WindingNO Output WindingNE Error Correction WindingSingle or Multi-StageInexpensive to ImplementVery AccurateCurrent Transformer Manufacture

Measurement ResultsGuildline Instruments Limited8Source - Fluke 5520 CalibratorMeasurement Guildline 7220 Power Analyzer (Patent Pending)8 Independent ChannelsCurrent and Voltage (3-Phase + Ground)Current 4 Channels in SeriesVoltage 4 Channels in ParallelMeasurement SetupPower Analyzer

CurrentError Correcting TransformerVoltageResistive Voltage DividerA/D24 Bit @ 100 kHz8 Independent ChannelsProcessorPC Based Tablet0.5 A 50 Hz Stationary Sinusoidal SignalAC Current from 5520 in SeriesIRMS (1) From 4 Independent ChannelsOne Measurement per Period500 Samples10 Seconds x 50 HzMax Noise per Channel About 30 ppmIncludes Noise from Fluke 5520Stationary Signal (1a)Stationary SignalCurrent Noise

Current Noise < 30 ppm0.5 A 50 Hz Stationary Sinusoidal SignalAC Current from 5520 in SeriesIRMS (0.2s) From 4 Independent ChannelsMeasurement Based on Average (i.e. Aggregate) of 10 Adjacent Periods600 Reported Measurements120 Seconds x 50 Hz / 10 (Averaging)Max Noise per Channel About 15 ppmAveraging Acts Like a FilterIncludes Noise from Fluke 5520Stationary Signal (2)Stationary SignalAveraging Filter

Aggregation / Average of 10 MeasurementsNoise Reduced to About 15 ppmSame 0.5 A 50 Hz Stationary Sinusoidal SignalIRMS (1) From 4 Independent ChannelsMoving Sample Window of 30 MeasurementsUsed to Calculate Standard DeviationStandard Deviation About 3 ppm for Each Current MeasurementSuggests Most of the Type A Uncertainty is from the SourceMaximum Standard Deviation Spread on All 4 Current Measurements About 3 ppmHigh Level of Measurement Consistency

Stationary Signal 1(b)

Stationary SignalStandard Deviation

Standard Deviation Each Channel About 3 ppmMax Std Dev Spread 4 Channels About 3 ppmSame 0.5 A 50 Hz Stationary Sinusoidal SignalIRMS (3s) From 4 Independent ChannelsMeasurement Based on Average (i.e. Aggregate) of 150 Adjacent Periods3 Seconds x 50 Hz500 Reported Measurements (i.e. 10 Min)Max Noise per Channel About 10 ppmLonger Period of Averaging Improves FilterIncludes Noise from Fluke 5520Reported Signal Very Similar on 4 ChannelsImplies Signal Noise Dominated by SourceStationary Signal 3(a)

Stationary Signal Long Averaging Filter

Aggregation / Average of 150 MeasurementsNoise Reduced to About 10 ppmSame 0.5 A 50 Hz Stationary Sinusoidal SignalIRMS (3s) From 4 Independent ChannelsMoving Sample Window of 30 MeasurementsUsed to Calculate Standard DeviationStandard Deviation on 4 Independent Channels has Almost Identical TracesAgain Suggests Most of the Type A Uncertainty is from the SourceSuggests Type A Uncertainty of Current Transformers is < 4 ppmAlso Shows Very Good Measurement Consistency

Stationary Signal 3(b)

Stationary Signal - Standard Deviation with Filtering

Standard Deviation of 4 Independent Channels < 4 ppm50 Hz 0.45 / 0.5 Amp Stationary Sinusoidal SignalFluke 5520 Generated 0.45 and 0.5 AmpsMeasured by the Same Current TransformerSignals Pasted at Zero CrossingSignal with Current Transient Input into Power AnalyzerRepresents a 10% Change in Current Amplitude in 1 Period (i.e. 100,000 ppm)IRMS (1) Shows Power Analyzer Settled Within 3 Measurements to < 10 ppm (i.e. 60 msec)10 ppm Includes Fluke 5520 Noise0.05 Amp (10%) Transient

10% Current TransientRising Edge (100,000 ppm)

Settled Within 3 Periods < 10 ppm0.5 Amp 50 / 60 Hz Sinusoidal SignalFluke 5520 Generate 50 Hz and 60 HzMeasured by the Same Current TransformerSignals Pasted at Zero CrossingSignal with Frequency Transient Input into Power AnalyzerRepresents a 20% Change in Frequency in 1 PeriodIRMS (1) Shows Power Analyzer Settled Within 1 Measurement to < 10 ppm (i.e. 20 msec)10 ppm Includes Fluke 5520 Noise10 Hz (20%) Frequency Transient

20% Frequency Transient

Settled Within 1 Period < 10 ppmApplications and ConclusionsGuildline Instruments Limited25ApplicationsCurrent TransformerAC Current MeterPower Analyzer (Patent Pending)

7220 Power Analyzer Engineering PrototypeConclusions-1Asynchronous Sampling With Modern Electronics Equivalent to Phase LockingAveraging Filter Improves Performance by 100% - 300%Comparing Standard Deviation on Different Channels with Same Signal Helps Identify Type A Uncertainty Contribution from SourceConclusions-2Implemented Into Power Analyzer with Current Measurements < 10 ppmError Correcting TransformerFast Wide-Band A/D ConvertersImproved Processing AlgorithmsMeasures Both Stationary and Quasi-Stationary SignalsGoal is to Improve to < 5 ppmProviding Precision Measurement SolutionsGuildline Instruments Limited29