Communication%20Delays%20in%20Wide%20Area%20Measurement%20Systems%20(WAMS)

1
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

2
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.

3
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.

4
System Setup of WAMS
5
Phasor Measurement Units
6
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.

7
Technique behind PMU

• Samples are used to calculate the fundamental
  frequency component phasor magnitude and phasor
  angle.
• X phasor, N total number of samples, xk
  waveform sample
• The positive sequence phasor is then calculated
  as

8
Applications of PMUs

• State estimation
• Instability prediction
• Adaptive relaying
• Improved control of power systems

9
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

10
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
11
Communication Options

• Telephone lines
• Fiber-optic cables
• Satellites
• Power lines
• Microwave links

12
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

13
Delay Calculations

• The total delay can be expressed as
• fixed delay
• link propagation delay
• L amount of data transmitted
• R data rate of the link
• associated random delay jitter

14
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

15
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

16
Delay Calculation Table
Communication link Associated delay one way (milliseconds)
Fiber-optic cables 100-150
Microwave links 100-150
Power line (PLC) 150-350
Telephone lines 200-300
Satellite link 500-700
17
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.