Etienne Moulin Analog Devices Inc., MEASURING HARMONIC ENERGY WIT
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METER COMPONENTS
Etienne Moulin Analog Devices Inc.,
MEASURING HARMONIC ENERGY WITH SOLID-STATE ENERGY METER
static energy meters listed 62053-21 (previously 61036) accurately represent current drawn non-linear loads. these tests mention presence harmonics voltage input, implying definition active power calculation that harmonic power present. However, common side effect non-linear loads distortion line voltage, leading appearance harmonics voltage input. example, resultant harmonic power been measured field 9.3% total active power flow with signals 50th harmonic Such numbers demonstrate that ability measure harmonic active power critical traditional accuracy performances used classify energy meters. Defining realising test equipment capable simulating these conditions challenging basic characteristics electronic energy meter often sufficient determine solution measure harmonic active power what extent These criteria should used standard quality addition accuracy class meter when choosing electronic energy meter.
recent years, energy metering industry slowly adopted electronic solutions replace century-old electromechanical technology. advantages electronic solutions numerous. First, they bring industry into digital age, enable implementation value-added services such automatic meter reading (AMR) multi-tariff billing, maximum demand power quality monitoring.
lectronic meters also allow more accurate active power measurement including harmonics. Indeed, growing complexity household electrical equipment generates higher levels harmonics that should accounted active power measurement. Electromechanical solutions measure harmonic power only harmonic, while electronic solutions give accurate estimate above 63rd harmonic. Electronic solutions inherently precise. However, differences electronic system architecture impact accuracy harmonic active power measurement. This article summarises strengths weaknesses three major electronic energy meter implementations.
MEASURING HARMONIC POWER
main challenge when measuring harmonic power make sure that system measure harmonics voltage current inputs. important characteristics electronic system are: Analog input bandwidth analog input bandwidth defines frequency limit above which signal attenuated more than (29.2%). small analog input bandwidth means that higher orders harmonics will correctly analysed. example, 500Hz analog input bandwidth limits harmonic measurement 10th order installation. best require analog input bandwidth greater than 4kHz, harmonics lower than 63rd will correctly processed system both Europe North America. Sampling digital signal processing frequency sampling frequency (Fs) speed which analog-todigital converter (ADC) sampling input signal. should noted that most, all, electronic energy meters ADCs. Nyquist theorem says that input signal contains frequencies higher than Fs/2, signal cannot correctly interpreted, sampling process changes digital equivalent frequency. This behaviour known aliasing. With analog input bandwidth requirement mind, sampling frequency
HARMONIC POWER IMPORTANT?
harmonic active power active power generated harmonic frequencies fundamental frequency North America Europe. these harmonics present both voltage input load current, harmonic active power generated Equation
Non-linear loads like home entertainment equipment, high efficiency lights, desktop computers adjustable speed drives (ASD) used heat pumps conditioners sources harmonic load currents voltage installations. Test conditions
Lundquist, Bollen, "Harmonic Active Power Flow Medium Voltage Distribution Systems", IEEE WM2000, Singapore 2000.
METERING INTERNATIONAL ISSUE 2003 www.metering.com
METER COMPONENTS
should least twice desired input bandwidth kHz: kilo-samples second (ksps). specifications like add-on, reactive energy measurements. will require complete re-engineering energy meter optimise code each function added. Energy Metering with cost proposed family products from Analog Devices, energy meter architecture partitioned differently combining digital signal processing component. advantage relieving from real time signal processing allows simple, cost 8-bit management communication tasks. From energy measurement perspective also following advantages: parts have high sampling rate ksps analog input kHz, enabling signal processing harmonic power 230th. Products family allow direct interface current voltage sensors without additional analog front end. Extensive filtering done parts, providing stable repeatable energy measurements. CONCLUSION Including harmonics active energy calculation improves billing accuracy grid management number nonlinear loads household appliances increases. absence standard procedure requiring measurement harmonic power, qualitative evaluation electronic energy meters help decide solution capable harmonic power measurement. (See Table With latest advances integrated circuit development, proposed family products from Analog Devices, energy meter designers provide harmonic energy measurements cost satisfy emerging requirements from energy providers.
ELECTRONIC ENERGY METERS SAME
From high level perspective, meters from different manufacturers have similar architectures. They usually comprised analog front interface with voltage current sensors; analog-to-digital converters change real world signal into digital information; digital signal processing compute energy information; microprocessor (MCU) manage system peripherals; finally undefined number peripherals like display, infra-red port, other communication media. (See Figure when looks more closely, critical choices made implementation this architecture determine behavioural differences systems presence harmonic power.
Figure Electronic architecture single-phase energy meters
Multi-chip this case, emphasis choosing best performance right price, functions realised with individual electronic components each function listed Figure This architecture most expensive often used 3-phase applications. terms performance, ADCs critical elements chosen handle signal processing required energy calculation. 3-phase energy meters, 6-channel with simultaneous sampling, such AD73360L from Analog Devices, preferred choice. exceeds requirements accuracy measurement with sampling frequency 64ksps analog input bandwidth greater than kHz. This solution leaves signalprocessing algorithm hands meter manufacturer. with built-in This architecture attractive because ADCs, digital signal processing management functions combined component. Only extra analog components needed perform signal conditioning ADCs' inputs. leads compact design where energy data processing still responsibility meter manufacturer. However, several limitations should stressed: used this architecture limited digital signal processing (DSP) capabilities. result, only process inputs sampling rate e.g. ksps therefore limiting harmonic content included active energy measurement. Limited capabilities result lack filtering energy measurement. Poor filtering affects stability reproducibility results under test conditions where harmonics present. This stability valuable production shortens calibration test time. Such compact design will easily accommodate changing
Table Qualitative criteria evaluate harmonic measurement capability
ABOUT AUTHOR: Etienne Moulin application engineer Energy Measurement group Analog Devices Inc. located Wilmington, USA. Before joining Analog Devices worked electronic designer Thales (Thomson-CSF). graduated electrical engineering from Ecole Superieure d'Electricite France. ABOUT COMPANY: Analog Devices Inc. designs, manufactures markets highperformance analogue, mixed-signal digital signal processing integrated circuits used signal processing applications. company, founded 1965, headquartered near Boston, Massachusetts, manufacturing facilities Massachusetts, California, North Carolina, Ireland, Philippines Taiwan.
METERING INTERNATIONAL ISSUE 2003 www.metering.com
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