SECURITY CONSTRAINED ECONOMIC DESPATCH of Inter - state Generating Stations pan - India Detailed Feedback Report on Pilot March 2021 Power System Operation Corporation Limited SCED Pilot - Detailed Feedback Report – Mar 2021 Page 1 TABLE OF CONTENTS List of Figures ................................ ................................ ................................ ................ 4 List of Tables ................................ ................................ ................................ ................. 6 Executive Summary ................................ ................................ ................................ ...... 7 Disclaimer ................................ ................................ ................................ .................... 10 Use of Information from this Report ................................ ................................ ....... 10 1 Introduction ................................ ................................ ................................ ............. 11 1.1 Background ................................ ................................ ................................ ................................ .............. 11 1.2 Regulatory Framework ................................ ................................ ................................ .......................... 11 1.3 Provisions in Draft IEGC 2020 ................................ ................................ ................................ ............. 12 1.4 Regulatory Framework for Real - Time Market ................................ ................................ ................. 13 2 Implementation of Expanded SCED Pilot ................................ ............................. 14 2.1 Regulatory Provisions ................................ ................................ ................................ ............................ 14 2.1.1 Extending the period of SCED pilot ................................ ................................ .......................... 14 2.1.2 Expanding the scope of SCED pilot ................................ ................................ ........................... 14 2.1.3 Participation in the pilot ................................ ................................ ................................ ............... 14 2.1.4 Declaration of Variable Charges ................................ ................................ .............................. 15 2.1.5 Declaration of Technical Parameters ................................ ................................ ........................ 15 2.1.6 Sharing of System Savings ................................ ................................ ................................ .......... 16 2.1.7 Scheduling Process under RTM and SCED ................................ ................................ ................ 18 2.2 Expanding Ambit of SCED participating generators ................................ ................................ ...... 18 2.3 Challenges faced in implementation of expanded SCED pilot ................................ .................... 19 2.3.1 Declaration of Variable Charges by Generating Stations having par t - tied capacity .. 20 2.3.2 Treatment of capacity without having any Access in transmission system ......................... 21 2.3.3 Heat Rate Compensation ................................ ................................ ................................ ............. 22 2.3.4 Coal Linkage ................................ ................................ ................................ ................................ .. 22 3 SCED Development & Operation in 2020 ................................ ............................. 23 3.1 Implementation of RTM ................................ ................................ ................................ ......................... 23 3.2 New Scheduling Timelines ................................ ................................ ................................ ..................... 23 3.3 Higher ramp rates in thermal ISGS ................................ ................................ ................................ .... 25 3.4 Impact of COVID - 19 pandemic ................................ ................................ ................................ .......... 26 3.5 New features in SCE D ................................ ................................ ................................ ........................... 28 3.5.1 Modular Integration with RRAS ................................ ................................ ................................ .. 28 3.5.2 Incorporation of Export ATC ................................ ................................ ................................ ....... 30 3.5.3 Soft landing on exclusion ................................ ................................ ................................ ............. 30 3.5.4 Scheduled and Emergency Stop ................................ ................................ ................................ 31 3.5.5 Evacuation Limit ................................ ................................ ................................ ............................. 33 3.6 Reduction in Costs ................................ ................................ ................................ ................................ ... 33 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 2 3.7 Ease of generator operations ................................ ................................ ................................ .............. 40 3.8 Variations in Variable Cost ................................ ................................ ................................ .................. 42 4 Look Ahead SCED ................................ ................................ ................................ .... 47 4.1 Infeasibilities ................................ ................................ ................................ ................................ ............ 48 4.2 Cost Reduction ................................ ................................ ................................ ................................ ......... 49 4.3 RRAS Dispatch ................................ ................................ ................................ ................................ ......... 50 4.4 Availability of Ramp - constrained reserves ................................ ................................ ....................... 51 4.5 Ease of generator operations ................................ ................................ ................................ .............. 52 4.6 Schedule variability within look - ahead window ................................ ................................ .............. 53 5 Security Constrained Unit Commitment ................................ ............................... 57 5.1 Motivation ................................ ................................ ................................ ................................ ................ 57 5.2 SCUC Formulation ................................ ................................ ................................ ................................ .. 59 5.2.1 Objective function ................................ ................................ ................................ ......................... 59 5.2.2 Constraints ................................ ................................ ................................ ................................ ...... 59 5.3 Dovetailing SCUC to the existing framework ................................ ................................ ................... 61 5.4 Chang es to Web Based Scheduling Software (WBES) ................................ ................................ .. 62 5.4.1 Unit DC ................................ ................................ ................................ ................................ ............ 62 5.4.2 Pmax in WBES and SCED ................................ ................................ ................................ ............ 63 5.4.3 Pmin in WBES and SCED ................................ ................................ ................................ .............. 63 5.4.4 Requisitions by Constituents ................................ ................................ ................................ ......... 63 5.4.5 Unit De - Commitment through SCUC ................................ ................................ .......................... 63 5.4.6 Unit Commitment through SCUC ................................ ................................ ................................ 64 5.5 SCUC Case Study ................................ ................................ ................................ ................................ ... 64 5.5.1 Inputs and Assumptions ................................ ................................ ................................ ................. 64 5.5.2 Classification of Units in SCUC ................................ ................................ ................................ ... 65 5.5.3 Impact on Reserves ................................ ................................ ................................ ....................... 68 5.5.4 Change in schedule due to SCUC+SCED ................................ ................................ ................. 72 5.5.5 Unit Status ................................ ................................ ................................ ................................ ....... 76 5.5.6 Impact of SCUC on startups ................................ ................................ ................................ ........ 78 5.6 Optimization Formula tion of SCUC ................................ ................................ ................................ ..... 79 5.6.1 Notation ................................ ................................ ................................ ................................ .......... 80 5.6.2 Objective function ................................ ................................ ................................ ......................... 81 5.6.3 Startup and Shutdown Variables ................................ ................................ ............................... 82 5.6.4 Constraints ................................ ................................ ................................ ................................ ...... 83 5.7 Compensa tion for heat rate degradation ................................ ................................ ......................... 88 5.8 Startup Costs due to SCUC ................................ ................................ ................................ .................. 89 5.9 Settlement Related Issues under SCUC ................................ ................................ .............................. 89 6 Way Forward ................................ ................................ ................................ ............ 91 6.1 Extension of the SCED Pilot Project ................................ ................................ ................................ ..... 91 6.2 Need for SCUC pilot project ................................ ................................ ................................ ............... 91 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 3 6.3 Increase Frequency of Declaration of Variable Charges ................................ .............................. 92 6.4 Declaration of Incremental Heat Rate Curves ................................ ................................ .................. 93 6.5 Need to bring down Minimum Turn - Down Level ................................ ................................ .............. 93 6.6 Spinning (Hot) and Non - Spinning (Cold) Reserves ................................ ................................ ........... 94 6.7 National Pool Account ................................ ................................ ................................ ........................... 94 6.8 Statement of Station Heat Rate Degradation Compensation ................................ ....................... 94 6.9 Replication of SCED at Intra State level through SLDCs ................................ ................................ 95 6.10 Optimization considering full transmission network ................................ ................................ ......... 95 Annexures ................................ ................................ ................................ .................... 96 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 4 LIST OF FIGURES Figure 1 Composite Timeline for dispatch of SCED and RRAS (w.e.f. 19th September 2020) ................ 24 Figure 2 Block - wise ramp in post - SCED schedule of Talcher - II (Jan - Dec 2020) ................................ ......... 25 Figure 3 Average Net Schedule of SCED generators & All India Energy met ................................ ............ 27 Figure 4 Distribution of SCED SMP ................................ ................................ ................................ ....................... 27 Figure 5 Architectural overview of RRAS implementation ................................ ................................ ................ 29 Figure 6 Soft landing on exclusion ................................ ................................ ................................ ........................ 31 Figure 7 Scheduled and Emergency Stop in SCED ................................ ................................ ............................ 32 Figure 8 Daily cost reduction due to SCED (Jan 2020 - Jan 2021) ................................ ................................ 34 Figure 9 Daily Average Perturbation in SCED ................................ ................................ ................................ ... 35 Figure 10 Average SCED Perturbation vs Daily Cost Reduction ................................ ................................ .... 35 Figure 11 Daily Sale Volume in RTM by SCED generators ................................ ................................ ............. 36 Figure 12 Impact of RTM Trades on SCED Cost Reduction – study results ................................ ................... 37 Figure 13 Perturbation by SCED: Dec 2019 vs Dec 2020 ................................ ................................ .............. 37 Figure 14 Month - wise box plot of Variabl e Charges of SCED generators ................................ ................. 46 Figure 15 Trend of daily average cost of generation under SCED ................................ ............................... 46 Figure 16 Rolling look - ahead optimization window ................................ ................................ ......................... 48 Figure 17 Net Infeasibilities in SCED – Single period vs. Look - ahead ................................ .......................... 49 Figure 18 Cost reduction on sample days – Si ngle period vs Look - ahead ................................ .................. 50 Figure 19 RRAS dispatch on sample days – Single period vs Look - ahead ................................ ................. 50 Figure 20 Ramp constrained reserves on sample day – Single period vs Look - ahead ............................ 51 Figure 21 Duration curve of ramp constrained reserves over study period ................................ ................ 51 Figure 22 Ease of generator operations with SCED – Single period vs Look - ahead ................................ 52 Figure 23 Ch ange in All India ISGS schedule over day ................................ ................................ ................... 53 Figure 24 Net ISGS schedule within look - ahead run window ................................ ................................ ......... 54 Figure 25 Variability in block total schedule visibility over time ................................ ................................ .... 55 Figure 26 Variation of block total ISGS schedule across runs ................................ ................................ ........ 56 Figure 27 Regulation quantum duration available during 2019 - 20 (MW) ................................ ................. 58 Figure 28 Surplus of sell bids ove r buy bids in Day - Ahead Market in Power Exchange ......................... 59 Figure 29 Classification of units post SCUC ................................ ................................ ................................ ........ 66 Figure 30 Spinning Reserves comparison from 01 Jun to 03 Jun ................................ ................................ ... 67 Figure 31 Seasonal Transition of Reserves ................................ ................................ ................................ .......... 68 Figure 32 Ramp - constrained Reserves comparison ................................ ................................ ........................... 69 Figure 33 Spinning reserves comparison ................................ ................................ ................................ ............. 70 Figure 34 SMP Heat Map ................................ ................................ ................................ ................................ ...... 71 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 5 Figure 35 SMP vs Cheapest Cold Reserve ................................ ................................ ................................ .......... 71 Figure 36 Daily additional savings due to SCUC and startup costs ................................ .............................. 72 Figure 37 All India SCUC Schedule vs Actual Schedule ................................ ................................ ................... 73 Figure 38 ER SCUC Schedule vs Actual Schedule ................................ ................................ .............................. 73 Figure 39 NER SCUC Schedule vs Actual Schedule ................................ ................................ ........................... 73 Figure 40 NR SCUC Schedule vs Actual Schedule ................................ ................................ ............................. 74 Figure 41 SR SCUC Schedule vs Actual Schedule ................................ ................................ .............................. 74 Figure 42 WR SCUC Schedule vs Actual Schedule ................................ ................................ ............................ 74 Figure 43 IGSTPS Jhajjar SCUC Schedule vs Actual Schedule ................................ ................................ ....... 75 Figure 44 Dadri - II SCUC Schedule vs Actual Schedule ................................ ................................ ..................... 75 Figure 45 Solapur SCUC Schedule vs Actual Schedule ................................ ................................ .................... 75 Figure 46 Mauda - II SCUC Schedule vs Actual Schedule ................................ ................................ .................. 76 Figure 47 Unit status comparison for June 2020 to August 2020 ................................ ................................ .. 77 Figure 48 Unit status comparison for December 2020 to January 2021 ................................ ..................... 78 Figure 49 Startups Scatter plot ................................ ................................ ................................ ............................. 79 Figure 50 Diurnal startup pattern ................................ ................................ ................................ ......................... 79 Figure 51 Startup and Shutdown variables ................................ ................................ ................................ ........ 83 Figure 52 Illustration of Minimum up time (a)Valid (b)Invalid ................................ ................................ ......... 85 Figure 53 Illustration of Minimum up time (a)Valid (b)Invalid ................................ ................................ ......... 86 Figure 54 Illustration of Minimum down time (a)Valid (b)Invalid ................................ ................................ .... 87 Figure 55 Illustration of Minimum down time (a)Valid (b)Invalid ................................ ................................ .... 87 Figure 56 Illustration of crew constraint ................................ ................................ ................................ ............... 88 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 6 LIST OF TABLES Table 1 Generator wise SCED statement (Apr 2019 – Jan 2021) ................................ ............................... 38 Table 2 Generator - wise change in number of instructions and Delta MW ................................ .................. 40 Table 3 Distribution of Variable Charges of SCED Generators (Apr - 19 onwards) ................................ ... 43 Table 4 Month - on - month change in Variable Charges (Apr - 2019 onwards) ................................ .............. 44 Table 5 Differen ce between VC of successive generators in SCED merit stack (Apr - 19 onwards) ........ 45 Table 6 Inputs required for SCUC ................................ ................................ ................................ ........................ 61 Table 7 Proposed scheduling activities and timelines for SCUC ................................ ................................ ..... 61 Table 8 Cheapest and Costliest unit within each group ................................ ................................ ................... 66 Table 9 Units impacted by SCUC (Quadrants 2 and 4) ................................ ................................ .................. 66 Table 10 SCUC Cost Summary (Jun 2020 – Jan 2021) ................................ ................................ .................. 71 SCED Pilot - Detailed Feedback Report – Mar 2021 Page 7 EXECUTIVE SUMMARY The p ilot on SCED in ISGS p an - India has been implemented since 1 st April, 2019 The pilot helped to explore the scope of optimization on pan - India basis. The total production costs in ISGS are minimized without major structural changes in the prevailing scheduling and settlement system. Central Commission, on 18 th April, 2020, directed the extension and expansion of the pilot on SCED till 31st March, 2021. A detailed feedback report on the pilot was submitted to the Commission in January 2020. The present report would cover the experience of the pilot and feedback of activities during the extended & expanded pilot. Durin g the period of the expanded pilot, the SCED application was further developed . The generating stations with part tied - up capacity and merchant generators were also included. RTM was operationalized entailing changes in scheduling timelines. Revamped optim ization - centric RRAS software was implemented. The formulations of Look Ahead SCED and Security Constrained Unit Commitment were also tested as part of pilot project. SCED application has been continuously improved over time with addition of new features. With growth in renewables, the inter - regional flow patterns are undergoing a seasonal and diurnal shift. In view of this shift, the SCED software has been modified to incorporate import as well as export ATC constraints on inter - regional schedules for all regions. A soft - landing feature has been added to SCED software, which ensures that generators return to their pre - SCED schedules following ramp rates on exclusion. T he SCED stop functionality was split into two types depending on the nature of event requi ring SCED to be stopped – Scheduled Stop and Emergency Stop. During contingencies in the grid operations, in order to facilitate quicker and more effective control of generation , the evacuation limit feature has also been added to SCED. 1600 MW of addition al generation capacity was added under the expanded pilot viz. Farakka - III (500 MW) , Korba - III (500 MW) and Jhabua (600 MW) In order to enable participation of merchant power plants, the sharing of required information by generators needed for SCED in scheduling interface (WBES) of R LDC was enabled . The required changes/modification in SCED software to accommodate the merchant power plant were also carried out Most of the partly - tied generators have signed PPAs with different basis of variable charges The challenge of d eclaration of v ariable c harges by g enerating s tations having part - tied SCED Pilot - Detailed Feedback Report – Mar 2021 Page 8 capacity was faced. The weighted average PPA rate of the generator was considered for the pilot which was also be applicable for the un - tied/merchant quantum. The t reatment of generation without having any a ccess in ISTS was also a challenge. I n order to inject power in ISTS , it is mandatory to obtain some form of access i.e., long - term, medium - term or short - term SCED schedules can , thus , be given for a maximum quan tum for which long - term, medium - term or short - term access has been obtained by the concerned generating station. The operation below the normative PLF (85%) would entail heat rate degradation compensation in accordance with PPA provisions and IEGC P artly - tied and merchant generators with verified PPAs having provisions of heat rate degradation compensation would be eligible for compensation With RTM in operation, RRAS and SCED dispatch is taking place after RTM and the URS available post - RTM and RRAS is used for SCED optimization. In order t o facilitate quick and automatic incorporation of RTM tra nsactions in schedules, an in - house software application was developed to provide an interface to power exchanges and WBES along with verification of margins and clearing of transactions The faster dissemination of schedule data for bidding decision in RTM has been facilitated through a secure API shared w ith generators and constituents With the implementation of RTM, new scheduling timelines came into vogue with the gate closure for DC and requisition revisions getting shifted from 4th time block to 7th/8th time block before dispatch block. The p an - India lockdown for containment of COVI D - 19 pandemic from 25th March 2020 onwards had an impact with demand reduc tion up to 25 - 30 % A significant portion of generation capacity went under reserve shutdown. T he re was corresponding reduction in DC on - bar and net schedule of SCED participating ge nerators. There was also an impact in SCED System Marginal Price due to demand reduction. During 2020 (Jan - Dec), the total reduction in variable cost of generation due to SCED was ₹ 752 Crores. From the start of the SCED pilot in April 2019 up to January 2 021, the cumulative savings in generation cost on All - India basis is ₹ 1624 crores. W ith the optimal fuel supply arrangements and rationalization of coal stock, the spread of variable charges is reducing pan - India. The reduction of spread of variable cha rges appears to SCED Pilot - Detailed Feedback Report – Mar 2021 Page 9 be one of the causes for lowering of SCED savings in 2020 vis - a - vis 2019 A look - ahead SCED algorithm has been developed and its operation and results have been sim ulated for a period of one week. The key driver for a look - ahead SCED implementation is reduction of potential infeasibilities as the model has a longer term visibility. I t was observed that for around 10% of time during the simulated week, ramping up reserves are zero even with the look - ahead model. This is owing to exhaust ed spinning reserves in ISGS. Introduction of unit commitment with SCUC would help in maintaining sufficient spinning reserves. An in - house Security Constrained Unit Commitment ( SCUC ) software has been built with t he objective to minimize the operation cost while also maintaining requisite reserves for a rolling 3 day window , in - line with draft IEGC 2020 . The operation costs comprise of energy cost s and startup cost s The spinning reserve would be required to be maintained to take care of the real time uncertainties like unit tr ipping, unit derating, errors in demand and RE forecast, and weather events. ISGS SCUC case study was run for an eight - month period from June 1, 2020 to Ja n 31, 2021 on a 3 - day rolling window basis. The different aspects of reser ves, unit status and changes in schedule during the case study period have been detailed in the report. The changes to the existing scheduling activities and timelines for SCUC have also been detailed in the report. Continuation of SCED and operationalization of SCUC with reserves appear to be the next logical interventions that can be taken up for ensuring security and economy in the Indian Power System. SCED Pilot - Detailed Feedback Report – Mar 2021 Page 10 DISCLAIMER Precautions have been taken by Power System Operation Corporation Ltd. (PO SOCO) to ensure the accuracy of data / information and the data / information in this report is believed to be accurate, reliable and complete. However, before relying on the information material from this report, users are advised to independently ensure its accuracy, currency, completeness and relevance for their purposes, and, in this respect, POSOCO shall not be responsible for any errors or omissions. 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SCED Pilot - Detailed Feedback Report – Mar 2021 Page 11 1 INTRODUCTION 1.1 Background The implementation of a Pilot on SCED in ISGS Pan India was directed by Central Electricity Regulatory Commission i.e. Cent ral Commission w.e.f 1 st April, 2019 1 for six mont hs which was extended upto 31 st March, 2020 2 and further upto 31 st May, 2020 3 The prime driver behind the pilot on SCED was to explore the scope of optimization and, therefore, the possibility of minimising the total production costs without major structural changes in the prevalent system. Central Commission, on 18 th April, 2020 4 , directed the extension and expansion of the pilot on SCED till 31 st March, 2021. During the period of the expanded pilot, new features in SCED application were added. The generatin g stations with part tied - up capacity and merchant generators were also included. Real Time Market (RTM) 5 was operationalized entailing changes in scheduling timelines . The formulations of Look Ahead SCED and Security Constrained Unit Commitment were also tested as part of pilot project. 1.2 Regulatory Framework As per the Central Commission direction, du ring the initial phase till May 2020, the pilot on SCED was implemented for the limited set of the thermal ISGS that are regional entities and whose tariff is determined or adopted by the Central Commission for their full capacity honouring the existing scheduling practices prescribed in the Grid Code. It was recognized that there would still be scope of optimisation through SCED after the gate closure which has been implemented as enabler for RTM. Since June, 2020, the participation in the expanded pilot has been opened to all willing generators pan - India by including generating stations with part tied - up capacity, merchant generators and intra - state generators in addition to already 1 http://cercind.gov.in/2019/orders/02 - SM - 2019.pdf 2 http://cercind.gov.in/2019/orders/08 - SM - 2019.pdf 3 http://cercind.gov.in/2020/orders/Suo - Motu_1 - SM - 2020.pdf 4 http://cercind.gov.in/2020/orders/8 - SM - 2020.pdf 5 http://cercind.gov.in/2019/regulation/1.%20Sta tement%20of%20Reasons_RTM_12_12_2019.pdf SCED Pilot - Detailed Feedback Report – Mar 2021 Page 12 participating generators. Upfront declaration of variable charges along with technical, operational and other parameters to the system operator has been mandated by the Central Commission. Further, new methodology for sharing of bene fits amongst the beneficiaries and the participating generators has been put in place. 1.3 Provisions in Draft IEGC 2020 The Central Commission constituted an Expert Group to review Indian Electricity Grid Code and other related issues in May, 2019. The expert group submitted the report in January, 2020 6 . The draft revised IEGC proposed by the expert group has the provisions to ensure and monitor availability of reserve capacity. The quantum of reserve capacity required to be maintained for grid security is rel ated to credible contingency including net error in the forecasts of demand and renewable generation. It is proposed that SLDC/RLDC may calculate the desired secondary reserve to be kept in their control areas at the beginning of each financial year and s ubmit to NLDC. The quantum of reserves earmarked for secondary would be based on the data of last year Area Control Error ( ACE ) , will be taking care of exceptional high values due to weather related phenomenon or any other exceptional circumstances. It is desirable that reserves may be provided locally by the control area. The responsibility to provide reserve response may be shared by all Control Areas in a distributed manner in the interest of grid security and in a participative manner so that the frequ ency is collectively controlled through ACE minimization Tertiary reserves may be arranged from the generating stations, Energy Storage Systems (ESS) and/or through demand response. Tertiary reserve has to be greater or equal to secondary reserves to take care of contingencies, and would be maintained at both regional entity level as well as state control area. Tertiary reserves will act as replenishment for secondary reserves as secondary reserves are to be restored back to their original level for prepar ation towards next contingency. 6 http://cercind.gov.in/2020/reports/Final%20Report%20dated%2014.1.2020.pdf SCED Pilot - Detailed Feedback Report – Mar 2021 Page 13 It has been proposed that the Security Constrained Unit Commitment (SCUC) exercise may be carried out to facilitate reliability of supply to the regional entities/beneficiaries taking into account optimal cost, adequate rese rves, ramping requirements facto ring security constraints . In order to ensure availability of adequate secondary and tertiary reserves with sufficient ramping capability, NLDC may identify the generating unit for purpose of unit commitment at the national level for regional entity generating stations on a 3 - day rolling basis. NLDC, through RLDC may advise the regional entity generators to commit or de - commit the unit. 1.4 Regulatory Framework for Real - Time Market RTM has been implemented with effect from 1 st June 2020 . The Real Time Market of electricity is an organized market platform which focuses on bringing in vital flexibility to manage real time balance and at the same time it also facilitates optimal utilization of the available surplus generation in th e system. RTM for electricity has been intended for thirty minutes delivery period in two consecutives fifteen - minute time blocks at regular intervals during the day which implies RTM has 48 sessions in a day starting from 00:00 hrs up to 24:00 hrs. The me chanism for price discovery has been adopted as double - sided closed auction with uniform price discovery. Members participating in the Real Time Market have the choice of setting buy and sell offers for each fifteen - minute time block in the half hourly Rea l Time Market. To bring in firmness in the schedule and transactions in real time, Gate Closure has been introduced. SCED Pilot - Detailed Feedback Report – Mar 2021 Page 14 2 IMPLEMENTATION OF EXPANDED SCED PILOT 2.1 Regulatory Provisions 2.1.1 Extending the period of SCED pilot The Central Commission recognized that the scope of optimisation and, therefore, the possibility of minimising system cost steers the need for appropriate regulatory framework in the context. The optimization of the last - mile available resources through a RTM market platform was also envis aged. The scope of optimisation through SCED after the gate closure was considered. Accordingly, the Central Commission directed to extend the SCED pilot beyond 1 st June, 2020, for a further period up to 31 st March, 2021. 2.1.2 Expanding the scope of SCED pilot The Central Commission also decided to expand the ambit of SCED by including the generators other than the regulated thermal ISGS. During the extended period, the SCED pilot would be open to all generating stations that are willing to participate during t he extended period upto 31 st March, 2021. These include generating stations owned by the State entity and having capabilities to communicate with RLDCs/ NLDC; generating stations whose scheduling is done by RLDCs; and State - embedded generating stations who se scheduling, metering, accounting and settlement is in place and whose scheduling related information exchange can be enabled through the SLDC interfacing with the concerned RLDC/ NLDC. Scheduling for those generators that are done through SLDC, shall co ntinue to be done by the respective SLDC while increment/ decrement instructions under SCED shall be communicated from NLDC/ RLDCs to the respective SLDC. 2.1.3 Participation in the pilot Generators already participating in the SCED pilot would continue to part icipate in the Pilot for the extended period. Other generators willing to participate in the extended period are required to provide a one - time consent for participation in SCED SCED Pilot - Detailed Feedback Report – Mar 2021 Page 15 pilot. Once the consent is communicated to POSOCO, it is mandatory for the gen erator to participate in the SCED pilot for a minimum period of one month. Such generators would declare their variable charge upfront, similar to the existing SCED generators participating in the pilot. 2.1.4 Declaration of Variable Charges Variable charge of g enerators other than the ISGS whose tariff is determined by the Commission is considered as under: a) For generators having full capacity tied in multiple PPAs, variable charge shall be considered as the weighted average of the variable charges, as determined or adopted by the Appropriate Commission. b) For generators having only part capacity tied in PPA(s), variable charge shall be considered as the weighted average of the variable charges, as determined or adopted by the Appropriate Commission for the contract ed capacity shall be considered for the untied portion of the capacity as well. c) For generators with no tied capacity (merchant generator), variable charge shall be considered as intimated by such generator at least one week in advance to POSOCO. The genera tors shall be required to declare the variable charge on monthly basis. 2.1.5 Declaration o