Atmel's AT73C500 AT73C501-based meter chipset measures power energy th

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Power Meter Front Design: Delta Connection
Atmel's AT73C500 AT73C501-based meter chipset measures power energy three-phase systems alternatively, chipset operate mode where measures three separate, single-phase connections. normal modes operation, chipset measures Y-connected threephase, four-wire environments, there dedicated operating mode Delta-connected three-phase, three-wire systems. This application note describes implement chipset threephase, three-wire environments. Phase Current (IP1, IP3) current flowing through load impedance. Depending type connection, this current necessarily directly measurable from meter connection points, must derived from vector other currents. Main Current (I1, defined current that flows through phase conductor. Depending type connection, this current necessarily same that flows through load.
Power Meter Front Design: Delta Connection Application Note
Three-Phase Basics
understand measurement method, important outline some following basic concepts. Terminology Voltages (and currents) three-phase system referred either phase voltages (currents) main voltages (currents), depending point reference. Phase Voltage(1) (UP1, UP3) always referenced neutral wire. systems where there physical neutral wire, phase voltages referenced virtual neutral.
Note: Also called neutral voltage. This should confused with ground neutral that zero potential.
Star Connection
typical three-phase, four-wire service with grounded neutral illustrated Figure system shown commonly referred YN-configuration, with subscript denoting there neutral wire present. wiring method sometimes also referred Star connection. Figure circuit left illustrates power generator circuit right load. this type connection, energy meter would interface measure phase voltages phase currents (IP1, IP3). balanced (all loads equal) Star connection, neutral line carries current main current equal phase current. main voltage related phase voltage follows:
Main Voltage (U1, defined voltage between phase conductors.
Rev. 1680A-07/00
Figure Three-phase, Four-wire, YN-connection
Delta Connection
number wires reduced from four three, load wired Delta-configuration. noted that generator does necessarily have wired Deltaconfiguration, also Star-connected. example both generator load-connected Delta-configuration illustrated Figure connection Figure contains neutral wire inherent voltage marking therefore refers main voltages Figure Three-phase, Three-wire, Delta Connection (measured between phase conductors). When recalculating main voltages phase voltages, voltages referenced virtual neutral wire. noted, that balanced Delta connection, relationship between phase current main current
VIRTUAL GROUND POTENTIAL
Meter Front Design
Meter Front Design
Front Connections
schematic diagram page shows method connecting converter three-wire service. example Delta connection rated 230/400V system, easily adapted other rating. front should allow voltage overhead, specified standards (see Table achieve ratings Table start defining resistors kohm, get:
Voltage Front
transformers (Tr1 Tr2) together with resistor network through convert main voltages phase voltages. conversion factor (the number primary windings number secondary windings) transformers 1:1. Resistors must scaled match voltage system order inputs exceed maximum peak rating volt. voltage maximum should reached maximum main voltage system front end. assumed that main voltage equal three phases and, therefore, that maximum input voltage converter, calculated from following:
UPFS UPFS UPFS
380kohm
Using standard valued resistor kohm, maximum voltage this configuration will approximately 275V (i.e., about 390V peak amplitude). voltage maximum should later fine-tuned 270V during factory calibration. above calculations repeated adapt design voltage system, maximum voltage meter front must considered when reading data pulses from meter. should noted that default resolution data registers meter constant pulse outputs based 270V maximum voltage. should also noted that measures phase voltages Delta-connected load. example, meter software ATEK5003 (The Evaluation AT73C500 chipset) displays voltage values with respect phase voltage main voltage.
assume system where phase voltage 230V and, consequently, main voltage 400V. analog Table Voltage Ratings Various Circuit Nodes
Path Node Phase1 Phase2 Phase3
Voltage
Symbol
Nominal
Maximum
Unit VRMS
Tr1/3 Tr1/4 Tr2/4 Tr3/Primary Tr4/Primary Tr5/Primary
VRMS
0.602
0.707
VRMS
ARMS
Current
0.707
VRMS
Current Front
Current transformers Tr3, used sensing phase current, which goes through primary winding. transformers should have conversion factor, such that, maximum rated phase current, secondary current, which goes through shunt resistors (R7, does produce more than 1-volt peak amplitude input. higher conversion factor transformer, lower value shunt resistor vice versa. should noted that high resistive values, signal distortion current transformer low, thermal noise resistor high. other hand, resistive values, thermal noise lower, power dissipation resistor higher. addition, current transformer distort signal load secondary winding high. compromise, example wiring uses current transformers with conversion factor 2500 shunt resistors ohms. full-scale current rating 80A, which voltage input
equal, Delta-configuration this must accounted for.
Measurement Method
uses same calculation methods, regardless type connection, since there special mode setting connecting device Delta load. differences measurement method, compared default Star connection wiring front conditioning signal amplitudes. Using front connections illustrated schematic page will measure phase voltages main currents each phase. measurement results, available data registers, necessarily give straightforward indications condition phase loads Delta connection. example, values phase voltages main currents cannot used derive power consumption phase load, since Delta-wired load connected between phase nodes, shown Figure will give measurement results load connected Star. Measurement results must therefore related equivalent Star connection shown Figure Please note that load impedances equivalent connection same those actual Delta connection. example, active power readings phase indicates much power been consumed equivalent load much power been consumed true loads Delta connection.
0.704V 2500
peak amplitude input then:
0.9956V
should noted that current measured chipset main current. Start Connection, this importance, since phase main currents Figure Delta-connected Load
VIRTUAL GROUND POTENTIAL
Meter Front Design
Meter Front Design
Figure Equivalent, Unbalanced Star Connection without Neutral Wire
VIRTUAL GROUND POTENTIAL
Summary
Delta-configuration, data registers should interpreted shown Table Table Delta-configuration
Variable TIME FREQ Register Current Main current Voltage Phase voltage Active Power Exported Total power loads Active Power Imported Reactive Power, Ind. Load Total powerin loads Reactive Power, Cap. Load Time Since Reset Line Frequency affected affected Power Factor Between main current phase voltage Apparent Power Power consumed equivalent phase load Reactive Power Power consumed equivalent phase load Active Power Power consumed equivalent phase load Measure Note
Typically, importance individual phase powers reported relative Star Delta connection, long overall power readings correct. Regardless chipset wired default Star load Delta load, illustrated schematic page overall power readings always obtained summing individual phase registers. When wired Delta load, must noted that individual phase power information correct only special case
when both generator load balanced. load supply unbalanced (even generator balanced, impedances transmission lines result unbalanced voltages), then only individual phase power readings will valid Delta connection. Individual phase powers cannot evaluated unbalanced Delta load.
Meter Front Design
Meter Front Design
Figure Front Connection Schematic
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1680A-07/00/xM
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