Transcript Instrument Transformer Communication

Digital Input Power Meter
Darrin Marr
Marcie Webb
Brad Zarikoff
1
Introduction
• Background
• Design and operation
• Progress and problems encountered
2
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
3
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
4
Conventional Technology
(Analogue Metering)
IPP tap from utility breakers
Current Sensor
Voltage Sensor
Optical Current
Electronics
DAC,
Amplifier
Optical Voltage
Electronics
DAC,
Amplifier
NXVCT
120V analogue
signal
Analogue Meter
- 0.2% accuracy over 2 – 3000A range
Utility owned equipment
IPP owned
equipment
Gas Turbine
Generators
225 MVA
13.8 kV, 60 Hz
138 kV
13.8 kV
Stn. Service Xfmr.
475 kW load
5
Metering with Digital Input
(Digital Metering)
IPP tap from utility breakers
Optical Current
Electronics
Current Sensor
Voltage Sensor
Merging
Unit
Optical Voltage
Electronics
NXVCT
Meter with digital
input
Utility owned equipment
IPP owned
equipment
Gas Turbine Generators
225 MVA
13.8 kV, 60 Hz
138 kV
13.8 kV
Stn. Service Xfmr.
475 kW load
6
Meters
Conventional
Analog Input Meter
P
User Display
Analog Signal
Conditioning
ADC
Digital Input Meter
P
User Display
101101010001
7
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”
8
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
9
Digital Input Power Meter
• Current and voltage emulation
• Current and voltage data merging unit
• Receiving and data decoding unit
• Data display
10
Digital Input Power Meter Layout
Sinewave
Generator
6 Channels
on one TDM
serial bus
Proprietary
Bit and
Sample Rate
Merging Unit
"Merges
Channels"
2.5 Mbps
4.8 kHz fs
continuous
16 bit
parallel
PC
Buffer Board
"Deserialize"
"Batch Type"
System
5760 Samples/0.2 s
11
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
12
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)
13
Packet Standard
• Packetized in accordance with IEC
60044-8 standard
• Packet standard incorporates threephase metering, protection, and unit
data, error control (CRC)
14
Merging Unit
S C o f E C T a (m e a s. )
S C o f E C T b (m e a s. )
S C o f E C T c (m e a s . )
S C o f E C T a (p ro t . )
S C o f E C T b (p ro t . )
S C o f E C T c (p ro t . )
M e r g i n g u ni t
S C o f E C T n e u t ra l
D i g ita l
o u tpu t
S C o f E V T b u sb a r
s u p p ly
S C o f E V T n e u t ra l
P o w e r
SC o f EVT c
C lo c k in p u t
SC o f EVT b
If r e q u ir e d
SC o f EVT a
M e r g in g u n it
p o w e r s u p p ly
15
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
16
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
17
Digital Interface Meter
Emmulation of a Digital Interface Meter
Digital Interface Meter
PC
Debug Board
Via Device
Driver or 3rd
Party
Software
Data File
(Specified
Maximum Size)
PCI
Data Aquisition Card
Via DB25
Connection
"Merged Data"
NRZ, 2.5 Mbps,
4.8kHz Sample
(Frame) Rate
DSP to Buffer Data Stream
2.5 MHz Serial
Clock
Read Only
Data "Snapshots"
Visual Basic GUI
18
Project Status
• Verification stage at present
• All design and implementation
complete
• Currently testing to ensure reliable
operation
• Visit our demo on Friday in ELW
19
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
20
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
21
Transmission Strategy
"Merged Data"
NRZ, 2.5 Mbps,
4.8kHz Sample
(Frame) Rate
Preliminary Merging Unit
2.5 MHz Serial
Clock
Manchester
Encoded Data
Optical
Transceiver
Manchester
Encoder
Optical
Fibre
"Merged Data"
NRZ, 2.5 Mbps,
4.8kHz Sample
(Frame) Rate
Manchester
Decoder
Digital Interface Meter
Manchester
Encoded Data
Optical
Transceiver
2.5 MHz Serial
Clock
22
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
23
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
24
Questions?
25