Transcript Communication Delays in Wide Area Measurements

Communication Delays
in Wide Area Measurement
Systems (WAMS)
Biju Naduvathuparambil,
Matthew C. Valenti, and
Ali Feliachi
Lane Department of Comp. Sci. & Elect. Eng.
West Virginia University
Preview of Talk
Idea: Communication delays in WAMS due to the
usage of phasor measurement units (PMUs).
Motivation: The use of innovative techniques like
PMUs in wide area protection systems in a
deregulated power industry.
Technique: PMU processing time, PMU data format
(IEEE 1344) length, and communication link
involved.
Wide Area Protection
Technical Advantage:
 Wide area protection (WAP) systems
(with the help of Phasor Measurement Units)
enhance system reliability by early detection and
immediate avoidance of possible catastrophic events.
Economics:
 WAP is an appropriate system for business support in an unbundled and
open-access utility environment.
 WAP is designed for an open-access market where production and
transmission patterns will more often change than in a closed market.
 WAP creates maximum profitability by reducing downtime and by
optimizing system performance.
System Setup of WAMS
PMU
PMU
PHASOR DATA
CONCENTRATOR
PMU
COMMUNICATION
LINK
APPLICATION
SOFTWARE
PMU
SYSTEM PROTECTION CENTER
MONITORING
CONTROL
DATABASE
Phasor Measurement Units
Pulses from GPS satellite
Analog power
signal
ANTI-ALIASING
FILTER
GPS RECEIVER
ANALOG TO
DIGITAL
CONVERTER
Phasor
Data
MICROPROCESSOR
Communication port
PMU Facts
• PMU uses discrete Fourier transform (DFT)
to obtain the fundamental frequency
components of voltage / current.
• Data samples are taken over one cycle /
multiple cycles.
• Currently, sampling is done at 12
samples/cycle (IEEE C37.111 Std.).
• Resolution of the A / D converter is 16 bits.
Technique behind PMU
Samples are used to calculate the fundamental frequency component
– phasor magnitude and phasor angle.
2 N
 j 2 k / N
X 
x
e
 k
N k 1
X = phasor, N = total number of samples, xk= waveform sample
The positive sequence phasor is then calculated as:
1
X1  ( X a  aX b  a 2 X c )
3
ae
j 2
3
Applications of PMUs
• State estimation
• Instability prediction
• Adaptive relaying
• Improved control of power systems
PMU Data Communication
• PMU communicates using the IEEE 1344
data format.
• IEEE 1344
– Data frame
• Information regarding phasor data
– Header frame
• Identification information about the PMU
– Configuration frame
• Number of phasors and digital channels
IEEE 1344
Type of
frame
Nature of data
Average length
(bits)
Data Frame
• Phasor information
• Channel digital input data
• Trigger status of frequency, angle,
Over-current, under-voltage
• Rate of frequency change
640
Header Frame
• PMU identification code
• Data source information
• Algorithms and filter data
200
Configuration
Frame
• PMU information
• Number of phasors and channels
• Nominal line frequency
• Transmission period of phasors
2800
Communication Options
• Telephone lines
• Fiber-optic cables
• Satellites
• Power lines
• Microwave links
Communication Delay Causes
• Transducer delays
• Window size of the DFT
• Processing time
• Data size of the PMU output
• Multiplexing and transitions
• Communication link involved
• Data concentrators
Delay Calculations
• The total delay can be expressed as:
L
   f  p  
R
 f fixed delay
 p link propagation delay
L amount of data transmitted
R data rate of the link
 associated random delay jitter
Delay Calculations……
• Fixed delay
– Delay due to processing, DFT, multiplexing and data
concentration
– Independent of communication medium used
– Estimated to be around 75 ms
• Propagation delay
– Function of the communication link and physical
separation
– Ranges from 25 ms in case of fiber-optic cables to
200 ms in case of low earth orbiting (LEO) satellites
Delay Calculations……
• The data length L of the PMU message is assumed
to be around 3640 bits (including data, header and
configuration frames)
• The data rate R is assumed to be around 33.6 kbps
for telephone lines and power lines. The data rate
R, for fiber-optic cables and microwave links, is
considered to be infinity for all practical purposes
Delay Calculation Table
Communication
link
Fiber-optic cables
Associated delay – one way
(milliseconds)
~ 100-150
Microwave links
~ 100-150
Power line (PLC)
~ 150-350
Telephone lines
~ 200-300
Satellite link
~ 500-700
Conclusion
• Communication delays play an important role in
determining the effectiveness of control
procedures
• Delay parameters presented can be integrated with
power systems design and analysis.
– Distributed control with outdated measurements.