Challenges of phasor measurement units

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Challenges of phasor measurement units

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Challenges of phasor measurement units

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

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