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Challenges of phasor measurement units

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Challenges of phasor measurement units

Challenges of phasor measurement units

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  • 1. Challenges of Phasor Measurement Unit (PMU)
    By
    Sarasij Das
  • 2. Content
    What is PMU?
    Why PMU?
    Applications of PMU
    Challenges of PMU
  • 3. What is PMU?
    Power system parameters represented as ‘complex numbers’
    Phasors contain magnitudes and angles
    Conventional instruments measure only magnitudes of phasors
    Local clocks used for time tagging of conventional digital instruments
    Inconsistent local clocks make it difficult to measure phase angles
  • 4. PMU measures magnitudes and angles of phasors at higher rates (10-60 samples/s) with accurate time tag
    PMUs can be found as standalone device (N60 of GE) or integrated with power system protection relay (L60, D60 of GE)
    Fig.1. GE N60 PMU [1]
  • 5. Fig.2. Block diagram of a PMU [2]
  • 6. Fig.3. Phasor representation
  • 7. Fig.4. Architecture of PMU based WAMS [3]
  • 8. Why PMU?
    Limitations of SCADA
    - Measurements obtained at slower rate (1 sample/1-4s)
    - Measurements are not time synchronised
    - Does not provide dynamic behaviour of system
    - Limited situational awareness conveyed to the operator
    - SCADA is ‘X-ray’ of power grid where PMU is ‘MRI’
    August 14, 2003 blackout:
    - Problems developed hours before the system collapse
    - System operators were unaware of overall worsening system
    conditions
  • 9. Applications [4]
  • 10. Challenges
    Consistent performance required for a multi vendor PMU system
    Diverse requirements from all utilities
    - different application requirements
    - difference in infrastructure
    WAMS architecture
    - present architecture not suitable for large system
    High investment
    - initial high investment requirement acts as an deterrent
    - clear roadmap is needed
  • 11. Challenges
    Lack of related products
    - not enough related products (PDC, application software)
    PMU placements - non-linear optimization problem
    - currently one can get sub-optimal solution
    Visualization of PMU data
    - difficult to visualise the voluminous data
    Communication of PMU data
    - expensive communication network required
  • 12. Challenges
    Communication delays
    - leads to delay in generating proper control signals
    Low frequency oscillation monitoring
    - algorithms are computationally heavy
    - all modes may not be captured
    - distorted power system waveforms make it difficult
  • 13. Challenges
    State estimation - deal with the hybrid system of PMUs and SCADA
    - bad data estimation
    On line voltage instability prediction
    - higher computational requirement
    - lack of system models are the main challenges for this
    of application.
  • 14. Reference
    [1] http://www.gedigitalenergy.com/multilin/catalog/n60.htm
    [2] “Phasor Measurement Unit (PMU) Implementation and Applications”, EPRI report, October 2007
    [3] “Synchronized phasor measurements and their applications”, by Arun G. Phadke, John Samuel Thorp
    [4] Chakrabarti, S.; Kyriakides, E.; Tianshu Bi; DeyuCai; Terzija, V.; "Measurements get together" Power and Energy Magazine, IEEE issue January-February 2009, Volume 7, Issue:1, page(s): 41 - 49

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