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

NEW Grid SR Grid Generation: MW Load: MW Export to SR: 3500 MW Generation: MW Load: MW Import from NEW: 3500 MW Assumptions: Initial frequency: Hz Capacity on bar in NEW Grid 93500/0.85 = say MW Capacity on bar in SR grid 26500/0.85 = 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 3500 MW

Effect of 1000 MW generation loss on tie-line flow to SR and frequency under various scenarios S noIncidentNo primary response in the entire system (A) 50% primary response in the entire grid (B) 50% primary response in NEW grid only (C ) 50% primary response in SR grid only (D)  Frequency and tie-line flow change  MW generation loss in NEW grid Hz 250 MW reduction in flow to South Hz 225 MW reduction in flow to South Hz 35 MW reduction in flow to South Hz 725 MW reduction in flow to South MW generation loss in SR grid Hz 750 MW increase in flow to South Hz 780 MW increase in flow to South Hz 965 MW increase in flow to South Hz 280 MW increase in flow to South

Observations 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 = (NI A - NI S ) – 10B (F A - F S ) - I ME – Where NI A is Actual Net Interchange – NI S is Scheduled Net Interchange – B is Control Area Bias – F A is Actual Frequency – F S is Scheduled Frequency – I ME 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 Hz

What 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 MW/Hz or % 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 paper

Setting Target Frequency Response Obligations NERC Reliability Standard Attachment A of BAL-003-1: Frequency Response and Bias Setting Standard

Setting Target Frequency Response Obligations NERC Reliability Standard Attachment A of BAL-003-1: Frequency Response and Bias Setting Standard Each control area target Frequency Response Obligation is worked out as

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 you

Computations for tie-line flows under various scenarios indicated above

Case 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 = Hz Post disturbance – Gen in NEW Grid = = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 3250 MW – Gen in SR Grid = MW (no change) – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = Hz Post disturbance – Gen in NEW Grid = (no change) – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 4250 MW – Gen in SR Grid = MW-1000 MW = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50 = MW/Hz ; SR grid primary response = MW capacity on bar x 0.40 x 0.50= 6240 MW/Hz; Combined primary response = MW/Hz Stabilized frequency = 50 Hz-(1000/( ) Hz = Hz Post disturbance – Gen in NEW Grid = ( x 21800) = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 3275 MW – Gen in SR Grid = MW + ( x 6240) = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = MW capacity on bar x 0.40 x 0.50 = MW/Hz ; SR grid primary response = MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50= 6040 MW/Hz; Combined primary response = MW/Hz Stabilized frequency = 50 Hz-(1000/( ) Hz = Hz Post disturbance – Gen in NEW Grid = ( x 22000) = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 4280 MW – Gen in SR Grid = MW ( x 6040) = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = MW capacity on bar after tripping of 1000 MW x 0.40 x 0.50 = MW/Hz ; SR grid primary response = 0 MW/Hz; Combined primary response = MW/Hz Stabilized frequency = 50 Hz-(1000/( ) Hz = Hz Post disturbance – Gen in NEW Grid = ( x 21800) = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 3465 MW – Gen in SR Grid = MW (no change) – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = MW capacity on bar x 0.40 x 0.50 = MW/Hz ; SR grid primary response = 0 MW/Hz; Combined primary response = MW/Hz Stabilized frequency = 50 Hz-(1000/( ) Hz = Hz Post disturbance – Gen in NEW Grid = ( x 22000) = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 4465 MW – Gen in SR Grid = MW-1000 MW = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = MW capacity on bar x 0.40 x 0.50 = 6240 MW/Hz; Combined primary response = 6240 MW/Hz Stabilized frequency = 50 Hz-(1000/( ) Hz = Hz Post disturbance – Gen in NEW Grid = = MW – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 2774 MW – Gen in SR Grid = MW + ( x 6240) = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW 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 = 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/( ) Hz = Hz Post disturbance – Gen in NEW Grid = MW (no change) – Load in NEW Grid = MW-( x 2700) MW = MW – Export to SR Grid = MW MW = 3780 MW – Gen in SR Grid = MW ( x 6240) = MW – Load in SR Grid = ( x 900) = MW – Import from NEW Grid = MW MW = 3780 MW Thus tie-line flow increases from 3500 MW to 3780 MW. Viz. 280 MW