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Effect of generation loss and Frequency Response Characteristics (FRC) on tie-line flow to Southern Region under various scenarios and Target setting for FRC and introduction of secondary control in Indian power system. Assumptions: Initial frequency: 50.00 Hz
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Effect of generation loss and Frequency Response Characteristics (FRC) on tie-line flow to Southern Region under various scenarios and Target setting for FRC and introduction of secondary control in Indian power systemAssumptions:
  • Initial frequency: 50.00 Hz
  • Capacity on bar in NEW Grid
  • 93500/0.85 = say 110000 MW
  • Capacity on bar in SR grid
  • 26500/0.85 = 31200 MW say
  • Frequency Response of load
  • 3% of load per Hz change uniform
  • Governor droop
  • 5% wherever primary response is there viz. 40% load per Hz
  • Losses ignored for simplicity
  • NEW GridGeneration: 93500 MWLoad: 90000 MWExport to SR: 3500 MW3500 MWGeneration: 26500 MWLoad: 30000 MWImport from NEW: 3500 MWSR GridEffect of 1000 MW generation loss on tie-line flow to SR and frequency under various scenariosObservations to note
  • Primary response is important on account of
  • Frequency stabilization post disturbance (case A1 & A2 vs others)
  • Minimize Under Frequency Relay (UFR) operations
  • Frequency stabilization in case of islanding of systems
  • Primary response cannot and does not
  • Influence tie-line loading under contingencies (A1/B1, A2/ B2);
  • hourly boundary flow change problem will remain; load-shedding will gradually get replaced by economy interchange over certain hours of the day as prevailing in systems worldwide.
  • Automatic Generation Control (AGC), if available, would bring down the tie-line loading to schedule in 8-10 minutes.
  • Skewed primary response can deteriorate tie-line loading
  • Case C2 and D1
  • Frequency Bias, B
  • Area Control Error (ACE) equation
  • ACE = (NIA- NIS) – 10B (FA - FS) - IME
  • Where NIA is Actual Net Interchange
  • NIS is Scheduled Net Interchange
  • Bis Control Area Bias
  • FA is Actual Frequency
  • FS is Scheduled Frequency
  • IME is Interchange (tie line) Metering Error
  • B should ideally be greater than or equal to ß, the control area frequency response (better to have slight over-correction).traditionally 1% of peak load/generation per 0.1 HzWhat does 1% of peak load/generation per 0.1 Hz translate to?
  • Governor droop setting is typically 5% which translates to 100% load change over 2.5 Hz frequency variation viz. 40% per Hz or 4% per 0.1 Hz.
  • Bias B of 1% per 0.1 Hz translates to 25% of ideal response of 4% per 0.1 Hz.
  • Even for the ENTSOE system with mean generation of the order of 306 GW,the overall FRC is of the order of 26000 MW/Hz or 20-25 % of ideal response.So ideal response appears to be a myth!!Reasons for decline in frequency response
  • Steam turbine generators operating on “sliding pressure” or “boiler-follower” control and/or with “valves wide-open” (VWO) operation.
  • Blocked governors on nuclear units for licensing reasons.
  • Less heavy manufacturing in North America (proportionally fewer large motor loads and a reduction in “load rejection”).
  • Variable-speed drives on motors that do not provide the traditional “load rejection”.
  • A larger proportion of combined cycle units on the system
  • In the past, many Control Areas carried full reserves for their individual largest contingency and some for multiple contingencies. De-regulation and competitive pressures have ended both of these practices.
  • NERC: Frequency Response white paperSetting Target Frequency Response ObligationsNERC Reliability Standard Attachment A of BAL-003-1: Frequency Response and BiasSetting Standard Setting Target Frequency Response ObligationsEach control area target Frequency Response Obligation is worked out as NERC Reliability Standard Attachment A of BAL-003-1: Frequency Response and BiasSetting Standard FRC Target in the Indian context
  • Minimum frequency: 49.8 Hz
  • First Stage of Under Frequency: 49.2 Hz
  • Largest contingency: 4000 MW UMPP
  • FRC > 4000 MW/0.6 Hz or 6666 MW/Hz if UFRs are not to operate
  • Assuming 25% margin this works out to
  • 8333 MW/Hz
  • Load response would be adequate only if All India load would reach 280 GW
  • Target would double if minimum frequency touches 49.5 Hz in normal course
  • 8333 MW/Hz might be only 16-17% of ideal response of the order of 50,000 MW/Hz.
  • Secondary Control
  • Secondary control
  • Tight control on deviations…….CERC is moving in this direction through pricing deviations and zero crossing
  • Area Control Error (ACE) could be introduced once FRC computations are on a sound footing and publicized so that Bias B can be fixed for each control area
  • Automatic Generation Control (AGC) could be introduced in phases
  • Outer loop operating from RLDCs to ISGS for frequency control and inter-regional tie line control
  • Inner loop operating from SLDCs to intra state generating stations for reducing control area ACE.
  • Thank youComputations for tie-line flows under various scenarios indicated aboveCase A1: 1000 MW generation loss in NEW Grid and no primary response in the entire grid; only 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = NIL; SR grid primary response = NIL; Combined primary response = NIL
  • Stabilized frequency = 50 Hz-(1000/3600) Hz = 49.7222 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500-1000 = 92500 MW
  • Load in NEW Grid = 90000 MW-(0.2778 x 2700) MW = 89250 MW
  • Export to SR Grid = 92500 MW -89250 MW = 3250 MW
  • Gen in SR Grid = 26500 MW (no change)
  • Load in SR Grid = 30000-(0.2778 x 900) = 29750 MW
  • Import from NEW Grid = 29750 MW-26500 MW = 3250 MW
  • Thus tie-line flow reduces from 3500 MW to 3250 MW. Viz. 250 MW
  • Case A2: 1000 MW generation loss in SR Grid and no primary response in the entire grid; only 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = NIL; SR grid primary response = NIL; Combined primary response = NIL
  • Stabilized frequency = 50 Hz-(1000/3600) Hz = 49.7222 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500 (no change)
  • Load in NEW Grid = 90000 MW-(0.2778 x 2700) MW = 89250 MW
  • Export to SR Grid = 93500 MW -89250 MW = 4250 MW
  • Gen in SR Grid = 26500 MW-1000 MW = 25500 MW
  • Load in SR Grid = 30000-(0.2778 x 900) = 29750 MW
  • Import from NEW Grid = 29750 MW-25500 MW = 4250 MW
  • Thus tie-line flow increases from 3500 MW to 4250 MW viz. 750 MW
  • Case B1: 1000 MW generation loss in NEW Grid and 50% primary response in the entire grid; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 109000 MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50 = 21800 MW/Hz ; SR grid primary response = 31200 MW capacity on bar x 0.40 x 0.50= 6240 MW/Hz; Combined primary response = 28040 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 28040) Hz = 49.9684 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500-1000 + (0.0316 x 21800) = 93190 MW
  • Load in NEW Grid = 90000 MW-(0.0316 x 2700) MW = 89915 MW
  • Export to SR Grid = 93190 MW -89915 MW = 3275 MW
  • Gen in SR Grid = 26500 MW + (0.0316 x 6240) = 26697 MW
  • Load in SR Grid = 30000-(0.0316 x 900) = 29972 MW
  • Import from NEW Grid = 29972 MW-26697 MW = 3275 MW
  • Thus tie-line flow reduces from 3500 MW to 3275 MW. Viz. 250 MW
  • Case B2: 1000 MW generation loss in SR Grid and 50% primary response in the entire grid; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 110000 MW capacity on bar x 0.40 x 0.50 = 22000 MW/Hz ; SR grid primary response = 30200 MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50= 6040 MW/Hz; Combined primary response = 28040 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 28040) Hz = 49.9684 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500 + (0.0316 x 22000) = 94195 MW
  • Load in NEW Grid = 90000 MW-(0.0316 x 2700) MW = 89915 MW
  • Export to SR Grid = 94195 MW -89915 MW = 4280 MW
  • Gen in SR Grid = 26500 MW-1000 + (0.0316 x 6040) = 25691 MW
  • Load in SR Grid = 30000-(0.0316 x 900) = 29972 MW
  • Import from NEW Grid = 29972 MW-25691 MW = 4281 MW
  • Thus tie-line flow increases from 3500 MW to 4280 MW. Viz. 780 MW
  • Case C1: 1000 MW generation loss in NEW Grid and 50% primary response in NEW Grid only; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 109000 MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50 = 21800 MW/Hz ; SR grid primary response = 0 MW/Hz; Combined primary response = 21800 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 21800) Hz = 49.9606 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500-1000 + (0.0394 x 21800) = 93359 MW
  • Load in NEW Grid = 90000 MW-(0.0394 x 2700) MW = 89894 MW
  • Export to SR Grid = 93359 MW -89894 MW = 3465 MW
  • Gen in SR Grid = 26500 MW (no change)
  • Load in SR Grid = 30000-(0.0394 x 900) = 29965 MW
  • Import from NEW Grid = 29965 MW-26500 MW = 3465 MW
  • Thus tie-line flow reduces from 3500 MW to 3465 MW. Viz. 35 MW
  • Case C2: 1000 MW generation loss in SR Grid and 50% primary response in NEW Grid only; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 110000 MW capacity on bar x 0.40 x 0.50 = 22000 MW/Hz ; SR grid primary response = 0 MW/Hz; Combined primary response = 21800 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 22000) Hz = 49.9609 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500 + (0.0391 x 22000) = 94360 MW
  • Load in NEW Grid = 90000 MW-(0.0391 x 2700) MW = 89895 MW
  • Export to SR Grid = 94360 MW -89895 MW = 4465 MW
  • Gen in SR Grid = 26500 MW-1000 MW = 25500 MW
  • Load in SR Grid = 30000-(0.0391 x 900) = 29965 MW
  • Import from NEW Grid = 29965 MW-26500 MW = 4465 MW
  • Thus tie-line flow increases from 3500 MW to 4465 MW. Viz. 965 MW
  • Case D1: 1000 MW generation loss in NEW Grid and 50% primary response in SR Grid only; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 0 MW/Hz ; SR grid primary response = 31200 MW capacity on bar x 0.40 x 0.50 = 6240 MW/Hz; Combined primary response = 6240 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 6240) Hz = 49.8984 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500-1000 = 92500 MW
  • Load in NEW Grid = 90000 MW-(0.1016 x 2700) MW = 89726 MW
  • Export to SR Grid = 92500 MW -89726 MW = 2774 MW
  • Gen in SR Grid = 26500 MW + (0.1016 x 6240) = 27134 MW
  • Load in SR Grid = 30000-(0.1016 x 900) = 29909 MW
  • Import from NEW Grid = 29909 MW-27134 MW = 2775 MW
  • Thus tie-line flow reduces from 3500 MW to 2775 MW. Viz. 725 MW
  • Case D2: 1000 MW generation loss in SR Grid and 50% primary response in SR Grid only; 3% per Hz load response
  • Load response of NEW Grid: 0.03*90000 MW= 2700 MW/Hz; Load response of SR Grid= 0.03*30000 MW = 900 MW/Hz; Combined load response= 3600 MW/Hz
  • Primary response NEW grid = 0 MW/Hz ; SR grid primary response = 30200 MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50 = 6040 MW/Hz; Combined primary response = 6040 MW/Hz
  • Stabilized frequency = 50 Hz-(1000/(3600 + 6040) Hz = 49.8963 Hz
  • Post disturbance
  • Gen in NEW Grid = 93500 MW (no change)
  • Load in NEW Grid = 90000 MW-(0.1037 x 2700) MW = 89720 MW
  • Export to SR Grid = 93500 MW -89720 MW = 3780 MW
  • Gen in SR Grid = 26500 MW -1000 + (0.1037 x 6240) = 26126 MW
  • Load in SR Grid = 30000-(0.1037 x 900) = 29906 MW
  • Import from NEW Grid = 29906 MW-26126 MW = 3780 MW
  • Thus tie-line flow increases from 3500 MW to 3780 MW. Viz. 280 MW
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