Synchrophasor Initiative in India - erldc

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SYNCHROPHASORS - INITIATIVE IN INDIA JUNE 2012Figure 70 shows that 1 second after occurrence of fault in Y-phase i.e., at 03:59:45.240 hrs,there is a rise in Y-Phase voltage whereas no rise in voltage in R & B phases. This rise in Y-phase voltage indicates closing of Y-pole which in-turn confirms auto-reclose of line. The timeobserved from PMU matches with the SCADA SOE time.Figure 71: Voltage profile at Dadri showing unsuccessful auto-reclosureFigure 71 shows the case of an unsuccessful auto-reclosure. Plot shows the 400kV Bus voltageof Dadri bus during fault in 400kV Dadri-Greater Noida line (current and voltage of this line is notwired to Dadri PMU). It can be observed that the 1 st fault occurred in R-phase which got clearedin 80milli seconds (approx) and 1 second after occurrence of fault there is 2 nd dip in R-phasevoltage which indicates that the R-pole of breaker tried to reclose but still fault was persisting.POSOCO Page 82 of 143
SYNCHROPHASORS - INITIATIVE IN INDIA JUNE 20125.4.2 Case Study-21: Validation of measurement cycle of df/dt relayRate of change of frequency (df/dt) relays have been provided to arrest the large drop in gridfrequency subsequent to a large generation loss. These relays are set to initiate automatic loadshedding whenever the frequency declines at a rate higher than 0.1 Hz/second. Operations ofdf/dt relay are reported by the State Transmission Utilities/State Load Despatch Centre in theregional protection sub-committee. On several occasions it was found that the relays hadoperated even when no generation loss had occurred. The df/dt data recorded bysynchrophasor during various grid incidents was examined. It was observed that df/dt during theinitial 40 ms was significantly high in comparison to the df/dt recorded after 100 ms. Theproblem was discussed with experts. It was learnt that the measurement of df/dt during thetransient condition (within the first few milliseconds of the fault) may be erroneous due to theinherent algorithm used for computation.Thereafter the df/dt recorded during the event of 2000 MW generation loss on 1 st June 2010 atRihand STPS was analyzed with different measurement cycles.Figure 72: df/dt observed at Vindhyachal with 40 ms plotFigure 72 above shows that the df/dt measured with 40milli seconds measurement cycle wouldbe between 1 to 1.6 Hz per second. Figure 73 shows the df/dt measured with 160 milli secondsmeasurement cycle would be between 0.6 to -1.2 Hz per second. Figure 58 shows that the df/dtmeasured with 200 milli seconds measurement cycle would be between 0.4 to -1.0 Hz persecond. Thus it could be inferred that the rate of change of frequency recorded by the df/dtinstalled at the various substation would depend on the measurement cycle.POSOCO Page 83 of 143
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Synchrophasor Initiative in India - erldc

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