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Darrin MarrMarcie WebbBrad Zarikoff

Digital Input Power Meter

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Introduction

• Background• Design and operation• Progress and problems encountered

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Project Goals

• To design a Power Meter that accepts a digital input

• Reduce the redundancy in conventional technology

• Improve on Power Measurement for Utility Industry

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Application Overview

• Power Meters are typically used in substations

• Current and voltage transducers feed power meters

• You cannot connect an oscilloscope to 138 000 volts

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Conventional TechnologyIPP tap from utility breakers

Analogue Meter

(Analogue Metering)

120V analogue signal

Current Sensor

Voltage Sensor

NXVCT

IPP owned equipment 138 kV

13.8 kV

Stn. Service Xfmr.475 kW load

Utility owned equipment

Gas Turbine Generators225 MVA13.8 kV, 60 Hz

Optical Current Electronics

DAC, Amplifier

Optical Voltage Electronics

DAC, Amplifier

- 0.2% accuracy over 2 – 3000A range

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Metering with Digital Input

Meter with digital input

(Digital Metering)

Current Sensor

Voltage Sensor

NXVCT

Optical Current Electronics

Optical Voltage Electronics

IPP owned equipment 138 kV

13.8 kV

Stn. Service Xfmr.475 kW load

Utility owned equipment

Gas Turbine Generators225 MVA13.8 kV, 60 Hz

IPP tap from utility breakers

Merging Unit

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Meters

P

User D

isplay

Digital Input Meter

101101010001

ADC P

Analog Signal

Conditioning

User D

isplay

ConventionalAnalog Input Meter

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Corporate Sponsorship

• NxtPhase is a company that makes Voltage and Current Transducers

• NxtPhase uses optics to measure the line voltage or current

• Optical signal is transduced to voltage and digitized

• Dedicated to “Digitizing the Grid”

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Keeping NxtPhase Happy

• NxtPhase does not make Power Meters

• Want to interface to next generation Digital Input Power Meters and Protection Relays

• Need to develop a Merging Unit to IEC 60044-8 standard

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• Current and voltage emulation• Current and voltage data merging unit

• Receiving and data decoding unit• Data display

Digital Input Power Meter

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Digital Input Power Meter Layout

Sinew aveGenerator

Merging Unit"Merges

Channels"

Buffer Board"Deserialize"

PC

6 Channelson one TDM

serial bus

ProprietaryBit and

Sam ple Rate2.5 Mbps4.8 kHz fs

continuous

16 bitparallel

"Batch Type"System

5760 Samples/0.2 s

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Sine Wave Generator

• Used to generate three-phase voltage and current received from NxtPhase equipment

• Simulates three voltage and current signals

• Output at NxtPhase proprietary data and sampling rate as TDM signal

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Merging Unit

• Takes TDM data of six sinusoids and packetizes them into data stream for transmission

• Outputs packets at 2.5Mbps at 4.8kHz sampling rate

• Continuous packet output (no idle)• Averages samples (NxtPhase sampling

rate much faster than IEC standard)

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Packet Standard

• Packetized in accordance with IEC 60044-8 standard

• Packet standard incorporates three-phase metering, protection, and unit data, error control (CRC)

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Merging Unit

SC of ECTa (meas.)

Merging unit

SC of ECTb (meas.)

SC of ECTc (meas.)

SC of EVTa

SC of EVTb

SC of EVTc

Digitaloutput

SC of EVT neutral

SC of EVT busbar

SC of ECTa (prot.)

SC of ECTb (prot.)

SC of ECTc (prot.)

SC of ECT neutral

Merging unitpower supply

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Buffer Board

• Transmission along data line to allow for remote monitoring

• Buffer board decodes data packet and buffers data (0.2s worth) for burst transmission

• National Instrument DAQ card dumps data into file on PC to be used by meter display

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Data Display

• Visual Basic in Excel application• Retrieves voltage and current data from

data file every x seconds• Formats and displays current and voltage

information• Calculates voltage and current spectrum,

power factor, and RMS values

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Debug Board

DSP to Buffer Data StreamPCIData Aquisition Card

Via DeviceDriver or 3rd

PartySoftware

Data File(Specified

Maximum Size)

Visual Basic GUI

D igital Interface M eter

PC

Read OnlyData "Snapshots"

Via DB25Connection

NRZ, 2.5 Mbps,4.8kHz Sample(Frame) Rate

"Merged Data"

2.5 MHz Serial Clock

Em m ulation of a Digital Interface M eter

Digital Interface Meter

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Project Status

• Verification stage at present• All design and implementation

complete• Currently testing to ensure reliable

operation• Visit our demo on Friday in ELW

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Problems Encountered

• No copy of Matlab for meter display development– Would have been excellent tool for data

display and manipulation • Now using Visual Basic in Excel

– Limited mathematical capabilities– Slow graphing capabilities

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Problems Encountered

• Original design included fiber optic link between Merging Unit and Digital Meter

• Researched options available– Found inexpensive development kit

• Lack of time forced us to abandon testing and implementation

• Fiber optics used to avoid EMI

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ManchesterEncoderPreliminary Merging Unit

ManchesterEncoded Data

OpticalTransceiver

O ptica lF ibre

ManchesterEncoded DataManchester

Decoder

NRZ, 2.5 Mbps,4.8kHz Sample(Frame) Rate

"Merged Data"

2.5 MHz Serial Clock

NRZ, 2.5 Mbps,4.8kHz Sample(Frame) Rate

"Merged Data"

2.5 MHz Serial Clock

Digital Interface MeterOptical

Transceiver

Transm ission Strategy

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Error Detection

• IEC 60044-8 standard includes CRC error detection code– Uses three 16-bit CRC checks

• Possible to have better error detection with less CRC bits required– One 32-bit CRC check would have

better detection capabilities

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Conclusions

• Digital input power meter currently not available commercially– NxtPhase has interest because need to

connect PT’s to digital meters• Realizable with more time• NxtPhase will be able to use Merging

Unit design as step towards useable product

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Questions?