Blackstart Restoration Plans for Western Region and Case Studies M.G.Raoot, P

Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008 Blackstart Restoration Plans for Western Region and case studies M.G.Raoot, P. Pentayya, Sachala Mishra and Haresh Patel Abstract— Since blackouts occur rarely, it would be difficult to of the disturbance in the NEW grid were hardly felt . train the system operators on restoration procedures. With However, the individual regions in the NEW grid are exposed significant loss to economy and great inconvenience to consumers, to both internal and external threats and a major contingency faster and efficient restoration is of utmost importance. This outside Western Region can have devastating effects in would require well documented detailed restoration plans tested through system studies, dispatcher training simulator, mock drills Western Region. Eventhough, major black outs appear to and creation of awareness the familiarity to not only system have remote chance, some incredible combination of events operators but also to operating personnel at generating stations may lead to a major disturbances encompassing the entire and sub-stations. The restoration plans also require suitable NEW grid. Such an eventuality may have far reaching revisions based on experience of actual restorations following consequences in terms of economic, political, national blackouts. The restoration plans for Western Region have been security, law & order spheres in addition to public revised incorporating the experience gained during the blackout on 30-07-2002. The paper discusses in detail the restoration inconvenience. It is therefore important to prepare restoration approaches followed in Western Region and frequently plans to restore power supply in the fastest possible manner. encountered restoration problems alongwith case studies taken At present, the existing plans envisage restoration of the from the restoration exercise following total system blackout on regions individually and inter connect the regions with each 30-07-2002. other after attaining adequate size and stability. This paper discusses the restoration plans for Western Regional Grid with Index Terms —interconnected power system, high-voltage, high-frequency, power system restoration emphasis on frequently encountered restoration problems which are illustrated through case studies. The last total black I. INTRODUCTION out in Western Region occurred on 30th July, 2002 and various incidents during restoration have been used as case studies to illustrate the restoration problems and constraints. he Indian Power System is operating as two asynchronous The Western Regional Grid comprise the states of grids viz. NEW grid comprising Northern, Eastern, T Maharashtra, Gujarat, Madhyapradesh (M.P), Chhattisgarh, Western, North Eastern grids in synchronous mode and Goa and the Union territories of Daman & Diu (DD), Dadra & Southern grid. The NEW grid is having installed capacity of Nagar Haveli (DNH). The installed capacity of Western 105856 MW and meeting peak demand of 90000 MW. The Region is 44894 MW and peak demand met is of the order of Southern grid is having installed capacity of 39695 MW and 29000 MW and energy consumption of 650MUs per day and meeting peak demand of 25000 MW. The formation of NEW peak deficit of around 9000 MW. A Grid Map of Western grid helped immensely all the regions synchronously Region is shown at Fig. 1 and also available at web link : connected through sharing of scarce generation resources , http://www.wrldc.com/maps/Powermapmarch2008.pdf. diversity of peak demands, improvement in hydro thermal mix, As there are no perfect solutions to prevent blackouts, which increase of system stiffness ( 1800 MW per Hz) and increased are usually caused by a complex sequence of cascading events, economy exchanges among the regions. The reliability of a number of different measures need to be undertaken to NEW grid also exhibited great improvement during the minimize the impact of future disturbances. The objective of disturbances like load crash due to weather effects, tripping of Recovery Procedures is to achieve restoration of total system number of lines due to fog, demand fluctuations are easily in the shortest possible time taking into account generation managed. The synergy of operating practices and uniformity securing (i.e., stabilization of saved units), start-up power to of defence mechanisms have also improved the security levels. nuclear units, essential loads, core sector industrial loads, the Loss of 3150 MW generation at Vindhyachal Power Station in generator capabilities and the transmission constraints and to Western Region on 22nd July 2008 could have led to a major achieve resynchronisation of constituent systems which have disturbance in Western Region operating alone but the effects separated from each other.The generic tasks of restoration include determination of system and equipment status, M. G. Raoot is with Powergrid Corporation of India Ltd. , WRLDC, preparation of plants and network for systematic restoration, Mumbai 400093 INDIA (phone: 91-22-28202691, 91-986955582; fax: 91- 22-28235434; e-mail: [email protected]). re-energization of the network, and system rebuilding. The P.Pentayya, is with Powergrid Corporation of India Ltd. , WRLDC, procedures for developing an effective restoration plan include Mumbai 400093 INDIA (phone: 91-022-28314609, 91-9869450206; fax: 91- formation of a qualified planning team, review of relevant 22-28235434; e-mail: ppentayya@ gmail.com). Sachala Mishra is with Powergrid Corporation of India Ltd. , WRLDC, system characteristics, formulation of assumptions regarding Mumbai 400093 INDIA (phone: 91-022-28302209, 91-9869450223; fax: 91- blackout scenarios, agreement on restoration goals, 22-28235434; e-mail: mishra_sachala@ rediffmail.com). development of strategy and tactics, validation of the plan, Haresh Patel is with Powergrid Corporation of India Ltd. , WRLDC, Mumbai 400093 INDIA (phone: 91-022-28302209, 91-9869404497; fax: 91- training, and documentation 22-28235434; e-mail: harsh_patel2k@ yahoo.co.in). 182 Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008 II. RESTORATION PLAN view load characteristics, ie., variation of load with respect to voltage and frequency and stiffness of island. During cold load pick up sudden starting of motor loads or power plant A. Situational Awareness auxiliaries like BFP, PA fan etc., can cause voltage dips due to System Operators at control centres should recognize drawal of high starting currents. Essential loads can be through Supervisory Control and Data Acquisition / Energy restarted in steps smaller than 5 MW. It is preferable to Management System (SCADA/EMS) tools the number of part restore rotating type loads which contributes to inertia of the systems/islands in the grid alongwith clear demarcation of island. In any case, load pick up should not cause frequency island boundaries. If possible by deploying additional staff, excursions greater than 0.5 Hz in the island.It is of utmost each island should be entrusted to one person who would be importance to identify the loads to be restored in advance and responsible for stabilization of island, to direct and monitor the document. progress of expansion of the island, restoration of essential loads in the island, to extend startup power to generators 2) Approach-II: outside the island and to synchronize the island with other The second approach could be followed in case self start islands for better stability. It is required to estimate the facilities are available at only a few power stations or the start stiffness (MW/Hz.) of the island by observing frequency up power has to be imported from neighbouring regions at one fluctuations and the generation/load in the island. As a thumb or two points. In this approach, the start up power required to rule about 3% of the load in the island can be considered as be extended to all the generating stations on priority basis stiffness to guide load restoration in steps. At least one unit in while restoring few loads and transformers for voltage control. the island can be assigned the role of frequency control by The start up power available from neighbouring regions at keeping the speed governor in frequency control mode. It is various interconnections have to be seriously explored since preferable to use all hydro and gas units to control frequency considerable assistance can be availed and the restored system through governor action and the droop setting of the governor is connected to stable external systems. The procedures have should be lowered to enable load pickup. to be laid down for quickly harnessing these facilities. The Transmission corridors used for startup power should be constituent receiving assistance during restoration process isolated from any damaged/faulty equipment and are of should restrict to the agreed quantum only since this may have minimum length and minimum voltage level to reduce line an adverse effect on healthy system rendering the assistance. charging Vars. Two distinct approaches are used depending on The restoration through this approach could be delayed due to the islanding schemes dispersal of black start facility and intra- problems in charging the lines, high-voltage, lack of regional connections. synchronising equipment at certain substations etc. and may involve system disturbances during restoration. The restored B. Restoration approaches [1] generators and loads are connected with the region supplying startup power assistance. Care

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