Blackstart Restoration Plans for Western Region and case studies M.G.Raoot, P. Pentayya, Sachala Mishra and Haresh Patel

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1 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 train the system operators on restoration procedures. With significant loss to economy and great inconvenience to consumers, faster and efficient restoration is of utmost importance. This would require well documented detailed restoration plans tested through system studies, dispatcher training simulator, mock drills and creation of awareness the familiarity to not only system operators but also to operating personnel at generating stations and sub-stations. The restoration plans also require suitable revisions based on experience of actual restorations following blackouts. The restoration plans for Western Region have been revised incorporating the experience gained during the blackout on The paper discusses in detail the restoration approaches followed in Western Region and frequently encountered restoration problems alongwith case studies taken from the restoration exercise following total system blackout on Index Terms interconnected power system, high-voltage, high-frequency, power system restoration T I. INTRODUCTION he Indian Power System is operating as two asynchronous grids viz. NEW grid comprising Northern, Eastern, Western, North Eastern grids in synchronous mode and Southern grid. The NEW grid is having installed capacity of MW and meeting peak demand of MW. The Southern grid is having installed capacity of MW and meeting peak demand of MW. The formation of NEW grid helped immensely all the regions synchronously connected through sharing of scarce generation resources, diversity of peak demands, improvement in hydro thermal mix, increase of system stiffness ( 1800 MW per Hz) and increased economy exchanges among the regions. The reliability of NEW grid also exhibited great improvement during the disturbances like load crash due to weather effects, tripping of number of lines due to fog, demand fluctuations are easily managed. The synergy of operating practices and uniformity of defence mechanisms have also improved the security levels. Loss of 3150 MW generation at Vindhyachal Power Station in Western Region on 22nd July 2008 could have led to a major disturbance in Western Region operating alone but the effects M. G. Raoot is with Powergrid Corporation of India Ltd., WRLDC, Mumbai INDIA (phone: , ; fax: ; mraoot5@yahoo.co.in). P.Pentayya, is with Powergrid Corporation of India Ltd., WRLDC, Mumbai INDIA (phone: , ; fax: ; ppentayya@ gmail.com). Sachala Mishra is with Powergrid Corporation of India Ltd., WRLDC, Mumbai INDIA (phone: , ; fax: ; mishra_sachala@ rediffmail.com). Haresh Patel is with Powergrid Corporation of India Ltd., WRLDC, Mumbai INDIA (phone: , ; fax: ; harsh_patel2k@ yahoo.co.in). of the disturbance in the NEW grid were hardly felt. However, the individual regions in the NEW grid are exposed to both internal and external threats and a major contingency outside Western Region can have devastating effects in Western Region. Eventhough, major black outs appear to have remote chance, some incredible combination of events may lead to a major disturbances encompassing the entire NEW grid. Such an eventuality may have far reaching consequences in terms of economic, political, national security, law & order spheres in addition to public inconvenience. It is therefore important to prepare restoration plans to restore power supply in the fastest possible manner. At present, the existing plans envisage restoration of the regions individually and inter connect the regions with each other after attaining adequate size and stability. This paper discusses the restoration plans for Western Regional Grid with emphasis on frequently encountered restoration problems which are illustrated through case studies. The last total black 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. The Western Regional Grid comprise the states of Maharashtra, Gujarat, Madhyapradesh (M.P), Chhattisgarh, Goa and the Union territories of Daman & Diu (DD), Dadra & Nagar Haveli (DNH). The installed capacity of Western Region is MW and peak demand met is of the order of MW and energy consumption of 650MUs per day and peak deficit of around 9000 MW. A Grid Map of Western Region is shown at Fig. 1 and also available at web link : As there are no perfect solutions to prevent blackouts, which are usually caused by a complex sequence of cascading events, a number of different measures need to be undertaken to minimize the impact of future disturbances. The objective of Recovery Procedures is to achieve restoration of total system in the shortest possible time taking into account generation securing (i.e., stabilization of saved units), start-up power to nuclear units, essential loads, core sector industrial loads, the generator capabilities and the transmission constraints and to achieve resynchronisation of constituent systems which have separated from each other.the generic tasks of restoration include determination of system and equipment status, preparation of plants and network for systematic restoration, re-energization of the network, and system rebuilding. The procedures for developing an effective restoration plan include formation of a qualified planning team, review of relevant system characteristics, formulation of assumptions regarding blackout scenarios, agreement on restoration goals, development of strategy and tactics, validation of the plan, training, and documentation 182

2 II. RESTORATION PLAN A. Situational Awareness System Operators at control centres should recognize through Supervisory Control and Data Acquisition / Energy Management System (SCADA/EMS) tools the number of part systems/islands in the grid alongwith clear demarcation of island boundaries. If possible by deploying additional staff, each island should be entrusted to one person who would be responsible for stabilization of island, to direct and monitor the progress of expansion of the island, restoration of essential loads in the island, to extend startup power to generators outside the island and to synchronize the island with other islands for better stability. It is required to estimate the stiffness (MW/Hz.) of the island by observing frequency fluctuations and the generation/load in the island. As a thumb rule about 3% of the load in the island can be considered as stiffness to guide load restoration in steps. At least one unit in the island can be assigned the role of frequency control by keeping the speed governor in frequency control mode. It is preferable to use all hydro and gas units to control frequency through governor action and the droop setting of the governor should be lowered to enable load pickup. Transmission corridors used for startup power should be isolated from any damaged/faulty equipment and are of minimum length and minimum voltage level to reduce line charging Vars. Two distinct approaches are used depending on the islanding schemes dispersal of black start facility and intraregional connections. B. Restoration approaches [1] 1) Approach-I: In systems with a fair dispersal of Generating stations with black start facilities, those generating stations where black start facilities are available, should be started up and islands formed around these generating stations by connecting essential loads. These islands are then interconnected at predefined locations where synchronizing facilities are available. The speed of restoration enhances with increase in number of black start facilities and their dispersal. Gujarat, Chhattisgarh and M.P have considerable number of black start facilities while Maharashtra suffers from lack of adequate number of black start generators. In some states like Gujarat, number of islanding schemes have been planned around generating stations with one or two units planned to island with radial loads. Such island can be used to extend startup power to neighbouring generating stations and the islands are expanded in a steady manner. It is required to carefully monitor the operation of the island (re-integration with rest of the grid) due to small stiffness in islands. Each island shall be independently managed and controlled. While adding loads, care should be taken to ensure step by step addition keeping in 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 auxiliaries like BFP, PA fan etc., can cause voltage dips due to drawal of high starting currents. Essential loads can be restarted in steps smaller than 5 MW. It is preferable to restore rotating type loads which contributes to inertia of the island. In any case, load pick up should not cause frequency excursions greater than 0.5 Hz in the island.it is of utmost importance to identify the loads to be restored in advance and document. 2) Approach-II: The second approach could be followed in case self start facilities are available at only a few power stations or the start up power has to be imported from neighbouring regions at one or two points. In this approach, the start up power required to be extended to all the generating stations on priority basis while restoring few loads and transformers for voltage control. The start up power available from neighbouring regions at various interconnections have to be seriously explored since considerable assistance can be availed and the restored system is connected to stable external systems. The procedures have to be laid down for quickly harnessing these facilities. The constituent receiving assistance during restoration process should restrict to the agreed quantum only since this may have an adverse effect on healthy system rendering the assistance. The restoration through this approach could be delayed due to problems in charging the lines, high-voltage, lack of synchronising equipment at certain substations etc. and may involve system disturbances during restoration. The restored generators and loads are connected with the region supplying startup power assistance. Care has to be taken while delinking the restored parts of the connecting links usually bypass links at High Voltage Direct Current (HVDC) back to back stations. The bypass links should be brought to floating (MW & MVAR close to zero) before opening. C. Restoration in Western Region The restoration procedures prepared and made available at State Load Despatch Centre (SLDCs) and Regional Load Despatch Centre (RLDC) define restoration paths for extending start up power to each power station clearly along with alternative paths and priorities of paths. The priorities are generally decided based on usage of short line sections and lower voltage lines. D. Generation securing High priority is given to ensure the survival of islands that have been created either by design or by chance. One engineer is assigned to each of these islands to monitor frequency control aspects as well as re-integration aspects. The power available from black started units is to be 183

3 extended based on defined priorities. Highest priority will be accorded for supply of survival power to the generating stations followed by to those units capable of hot start up, units capable of rapid restart and essential loads like traction. Normally, hydro and gas units are provided with black-start facilities. In case of non provision of black start facility or failure to black-start, hydro and gas units are given start-up power as these can come up with full load in about 10 minutes. E. Synchronizing locations The islands are re-connected/re-integrated at pre-defined locations and the substation/generating station engineers in Western region are well conversant with the procedures as well as synchronization of islands. III. FREQUENTLY ENCOUNTERED RESTORATION PROBLEMS A. Islanding schemes & Islanding on house load The black start procedures require that thermal units island on house load. However, except for the Trombay units, Tata Power Company (TPC) and Kakarapar (nuclear) units, the islanding on house loads is not generally successful. This is a major constraint. This facility would enable faster restoration of generators as some generators in each power station can go to house load operation and survive supplying their own auxiliaries. Even nuclear units can island on house load and kakarapar units successfully islanded on house load on In the steam dumping mode nuclear units can take care of load fluctuations easily. At present none of the thermal units are successfully islanded on house load which is a major constraint. Islanding schemes for power stations should be developed to enable islanding of one unit on house load and/or radial loads, particularly at those stations where small units are available. For instance, one unit at Dhuvaran is islanded along with radial 66kV loads. Availability of on-line power would enhance speed of restoration. On several islanding schemes successfully operated in Gujarat and helped in faster restoration. Islanding schemes of Utaran, GIPCL, ESSR, AE Co. (gas) and Kakarapar (nuclear) in Gujarat and TPC, REL islands in Maharashtra B. Maintaining active power balance 1) Load Generation Balance Maintaining load generation balance during step by step restoration of minimum and essential loads is required so that the islands restored will not collapse. On , the restored Koyna-Uran islands collapsed at 2245 hrs due to load generation mismatch. Further, frequency should be maintained around Hz to avoid tripping of units on low frequency. At 0117 hrs on , Uran Units-5 & 6 tripped on under frequency protection set at 47.5 Hz. At 0358 hrs, Uran Unit-5 once again tripped on high-frequency. However, the restored part did not collapse. 2) Low stiffness [2] The restored parts failed number of times during restoration or restoration delayed due to frequency control in islands with low stiffness. In small islands due to low stiffness frequency fluctuates widely even during load restoration. After restoring minimum possible load, the island should be synchronized with a larger island. The frequency fluctuations chart for the islanded Mumbai System look like Electro Cardiogram (ECG). During Grid disturbance on , the North Mumbai system had collapsed after islanding successfully due to its small size and low stiffness since the island is importing 40 MW prior to islanding. 3) Dynamic Reserve : It is essential to interconnect various islands at the earliest possible opportunity as the enlarged islands become more stable. On , tripping of Unit-4 (210 MW) of Ukai thermal power station resulted in collapse of AE.Co - GIPCL- Wanakbori-Gandhinagar-Ukai(H) islands. Similarly, the blackstarted Kawas & ESSAR Units in two different islands were synchronized to form one large island alongwith Ichhapur loads before extending startup power to Tarapur generators. Initially the under frequency relays are bypassed and after sufficient load is restored, about 25% of this load shall have feeders with UF relays energized so that adequate reserve would be available to take care of contingency of unit trippings. Dynamic reserve shall also be kept on on-line generators to take care of contingencies and to control frequency. C. Ramp up and response rate limitations of Black Started Units [2] Sometimes restoration delayed due to start up of large motors (auxiliaries) of thermal plants from black started gas units. Normally when thermal power station auxiliaries are energized from black started gas units, minimum auxiliaries essential for start up have to be energized. Out of the various auxiliaries, the largest motor has to be started first. The other motors are started thereafter one by one in a sequential manner (with larger ones preceding the smaller ones) as per the startup sequence. During restoration on [3], black started Kawas unit tripped as load restoration was too fast and in large increaments not consistent with Ramp up rate of Kawas unit (106 MW gas turbine) which is of the order of 7.6 MW per minute. Similarly, response rate violations (MW per Hz.) can also lead to unit trippings. The response rate depend upon the energy conversion process such as response of nuclear reactors, gas turbines, hydro turbines, boiler dynamics etc. 184

4 Some of the islands during restoration might collapse due to tripping of units or load restoration in large amounts compared to response rate of units, frequency prior to pick up of loads is too low (below 49 Hz). If the islands are built around gas based power plants, a constraint might arise in respect of restriction on multiple start-up and shutdowns. Documentation of number of startups and shutdowns a load and duration between two startups for emergency conditions is essential. Selection of loads to be restored in various islands from black started units should be identified in advance with respect to quantum of load to be restored in each step. This should be consistent with ramp rate and response of the units. Difficulties were faced while restoring loads from Jhanor power station during the occurrence occurred on Unbalancing of loads during the restoration procedure is a very serious phenomena and should be properly dealt with. D. Hunting problem in hydro units : While supplying start up power from small hydro units over long132kv/220kv lines, hunting of hydro units were observed number of times as depicted in Table I. Hunting of Bango units was reported due to voltage problems and charging of long section of lines during restoration of total blackout Power station (Hydro) TABLE I PERFORMANCE OF BLACKSTART FACILITIES ON Installed Capacit Remarks/ constraints y (Mw) Gandhisaga r Time taken For black start (Min.) Time taken for extending power to the next bus (Min.) 5x After 41 minutes start up power to Satpura power stations was extended. Voltage and MW hunting observed along the 132 kv start up path to Satpura. Pench 2x Start up power extended to Satpura Power station through 132 kv Pench-Seoni- Chhinwara-Satpura path. High-frequency problem and voltage hunting observed. Start up power could not be extended to Koradi power station of Maharashtra through 132 kv Pench-Kanhan line due to excessive voltage hunting. Bargi 2x Power extended up to Jabalpur. Due to high voltage problem power supply could not be extended to Amarkantak. Voltage The following action plan is drawn up in the Blackstart proceedings to counter the problem of hunting. 1) Start one unit keeping Automatic voltage regulator (AVR) out of service. Preferably, keep the excitation around 0.85 pu (as low as possible). At no load or reduced load on the machine rotor angle( ) will be small and as such under excitation is permissible. Take AVR into service only after the machine is loaded upto 10% to 15% and maintain frequency around 50 Hz. 2) At the remote end, charge one transformer with load of around 10% capacity of the machine (i.e 5 MW for Bargi machines or 7 MW for Pench machines). The transformer breaker is kept closed so that if the line is charged, the load immediately comes on the machine. It may be noted that hydro machines have good response rates. 3) Observe if any hunting occurs in active power, voltage or reactive power. If no hunting is observed, take AVR into service. If hunting is observed add more load at the remote end (i.e Jabalpur for Bargi units and Kanhan/Seoni for Pench units) till the hunting stops and then take AVR on auto mode. As the load is picked up on the machine, the excitation should be increased gradually. 4) With AVR in service throughout, it can be tested whether hunting occurs as it is suspected that the hunting problem is mainly due to activation of exciter modes. E. Delinking of restored parts from external systems: [4] Difficulties were also encountered in delinking from the external systems as the tie-lines have to be operated with almost zero active and reactive power for sometime. 1) On ,after availing start up power from Southern region through bypass link, Maharashtra restored units at Chandrapur, Bhusawal, Khaperkheda and Koradi. About 350 MW generation, loads in Nagpur area and traction supplies were restored by 0100 hrs on The bypass link was brought to floating conditions. At the time of opening 25 MW power was flowing towards SR. While disconnecting from SR, the islands collapsed with all generating units restored tripping on high-frequency. 2) On , Maharashtra once again availed start up power from Southern region at 0202 hrs. Start up power was extended to Chandrapur, Koradi, Khaperkheda, Parli and Bhusawal power stations by 0350 hrs. Traction loads were also restored fully in Eastern Maharashtra by this time. By 1000 hrs about 1950 MW generation and loads were restored. However, due to delay in restoration of loads, power upto 600 MW was exported to SR. This had caused alert situation in SR as number of 400kV lines got critically loaded and low voltages were also reported. At 1028 hrs, the bypass link was once again opened to take this island into the main western Grid, but the restored part of Eastern Maharashtra collapsed on low frequency. At the time of 185

5 opening, Maharashtra was restoring loads to keep the bypass link floating. Due to addition of more loads, power reversed with about 80 MW power flow towards Maharashtra system while frequency dropped to 47.7 Hz. When the bypass link was opened, 80 MW over load caused further frequency decay and collapse of the island. It is therefore essential to: a) Bring the bypass link to floating level and keep frequency around 49.5 Hz. b) Proper communication among SLDC Kalwa of Maharashtra, SLDC Ambazari of Maharashtra, Bhadravati HVDC stations and WRLDC has to be ensured. Once the link is brought to floating condition with frequency around 49.5 Hz, code for opening of the bypass link can be issued and no loads should be restored till the link is opened. F. High- voltage problems in restoration paths : 1) While extending start up power, high-voltages are usually encountered. The generating units supplying start up power are operated with excitation voltage as low as possible (much less than 1 p.u.). The non availability of radial load near some power stations (black started) is coming in the way of extending start up power to other stations due to high-voltage (e.g. Koyna). In case of highvoltage problems, we are restoring some loads along the restoration path usually of low power factor. 2) On , Koyna units were black started at 2020 hrs but power supply could be extended to Pedambe only at 2145 hrs. [4] The delay was due to high-voltages and lack of load at Pedambe. It is essential to identify loads at Pedambe so that power supply to Uran can be extended within a short duration as units at Uran can be brought back quickly. 3) On , restoration in Chhattisgarh was delayed as 400 kv lines could not be restored due to high-voltage problem. The attempts to extend start up power received from Southern and Northern regions failed repeatedly. This was due to non-availability of loads following long shutdown time due to black out and some industries declared compensatory holiday. G. High-voltage problems in extending start up power from hydro stations : Some of the major hydro stations like Koyna stage IV ( 4x250MW), Indira Sagar(8x125MW), Sardar Sarovar (6x200MW) are connected to only 400 kv and require charging of long 400kV lines which trip on high-voltage. It is required to start one hydro unit at these power stations with manual excitation kept at around 60% of normal voltage and charge the local 400kV bus. Then charge one shortest 400kV line and charge the remote end 400kV bus. Load should be restored immediately at the remote bus in small increments to control the high-voltage problem. Another alternative could be to supply block load equivalent to 10% of the remote end transformer capacity so that the moment the unit is synchronized to the 400kV bus block load would be incident. This would require keeping the line and transformer breakers as well as the breakers of feeders connecting to loads in closed condition prior to blackstarting the unit. One of the alternatives could be selected by carrying out mock drills. H. Operational practices and discipline : Ensuring of discipline when start up power is extended from one utility to other utility. Due to lack of adequate monitoring and control, some substation operators tend to restore more loads resulting in either overloading of start up path or unmanageable frequency variations.the substation operators have no documentation regarding load variations on various feeders over the day. The constituent receiving start up power should exercise proper control over their drawals. At times, the system providing assistance may collapse as this is too fragile. On , power supply was extended to Nasik by charging Nasik-Navsari D/C line at 0304 hrs. At 0355 hrs, Maharashtra drawal increased beyond 240MW with frequency of the restored Gujarat system touching 47.7 Hz. To save the restored part of Gujarat, GEB opened Nasik-Navsari lines (after warning) resulting in collapse of the Western Maharashtra islands comprising power stations of Koyna, Uran & Nasik. It is pertinent to point that due to cold load pick up, more load could have been restored than anticipated and system operators should factor in such possibilities. I. Identification/Selection of Load Selection of loads to be restored in various islands from black started units should be identified in advance with respect to quantum of load to be restored in each step. This should be consistent with ramp rate and response rate of the units. Difficulties were faced while restoring loads from Jhanor power station during the occurrence occurred on Unbalancing of loads during the restoration procedure is a very serious phenomena and should be properly dealt with. When traction loads are restored, phase balancing is an important consideration. If required some city loads on different phases can be restored along with traction loads. The feeders at the substations in the preplanned restoration path should be documented with MW, PF, MVAR parameters and their daily variation including timings of power-cuts. If voltage control during restoration is a priority then low power factor loads can be restored. J. Synchronisation of Islands One of the frequently encountered problem in restoration is due to non availability of synchronization facilities, trained manpower to carry out synchronization. On some occasions, 186

6 one of the islands collapsed due to jerk. In some cases the synchronization of islands was delayed due to lack of synchronization facilities and trained manpower. On , Eastern Maharashtra system was restored with startup power from SR while Western Maharashtra system was restored through blackstarting of Koyna Units. When both the parts of Maharashtra were having different frequencies. At 1002 hrs. 400kV Parli-Lonikhand Ckt-II was charged at Lonikhand in order to parallel both the parts of Maharashtra. While synchronizing at Parli, Jerk was observed and 400kV Indore-Asoj D/C tripped on powerswing. While charging two islands, it is preferable to charge and synchronise at the generating stations ends. At least, synchronising end must be a generating station. In addition, frequency difference should also be checked ( 0.1 Hz.). This would avoid sudden jerk. Further, charge at the end with maximum generation level. The restored island could be considered as stable if frequency deviations and voltage deviations are manageable and there are adequate active and reactive power reserves. The compliance of 25% load or generation as dynamic reserve is also important. With these conditions fulfilled, two critical and important islands can be synchronized with each other. The synchronization of two islands should not be done through weak ties. The restoration plans also stipulate for connecting two small islands quickly into a larger and more stable island. During restoration, a stable island system shall not be connected to a weak system On the synchronisation of Mumbai system (TPC & BSES system) with the rest of the grid was purposefully delayed due to delays in strengthening of Maharashtra system. It is also not advisable to operate islanded systems for such long durations due to the continuous frequency excursions and prolonged alert situation. Mumbai system was synchronised with MSEB system at 1541 hrs on It is therefore essential to speed up the restoration of the grid so that the survived islands could be saved from further trippings/collapse. It is also essential that TPC-BSES systems island together as it happened on 30th July so that the island survives properly and in case of delays in reconnection to the grid, the prolonged islanded operation may be secure with frequency/ voltage fluctuations minimised due to large size. In MP, the restored parts from black started Gandhisagar units as well as those from Bargi and Tons black started units should be quickly interconnected with each other as well as to NR supplies.this would hasten restoration process in MP. On considerable delays were experienced in connecting restored islands in MP to NR grid. [3] Standing Phase Angle problems have been encountered during restoration while re-integrating islands or re-connecting the state grids with each other. Normally, the state grids are reconnected after sufficient level of stabilization. The SPA problem is handled by generation re-scheduling based on the advice of RLDCs. At the synchronising end, control of standing phase angle (SPA) to less than or equal to 20 0 would help in minimising jerk or sudden rush of power. For reduction of SPA, the following measures need to be taken up. Reduce at those generators which are sensitive to the SPA. Shed loads at selected buses. Simultaneous backing down of generation and shedding of load. Increase of generation at the sensitive buses. The recommended practice for synchronizing lines is always through check synchronization relay which normally is set for 35 0 above which breaker closing is not permitted. For most of the lines, SPA < 35 0 would suffice. However, in case of lines inter connecting two major generating stations (Ex. 400kV Vindhyachal-Korba S/C line), it is prudent to limit the SPA to around However, for the sake of ready reference on the SPA control and sensitivity, measures to control SPA upto 20 0 have been provided. The measures such as generation reduction, load shedding etc., suggested for SPA control need not be exercised for upto On at 1000 hrs, 400kV Indore-Asoj lines tripped while synchronising Western Maharashtra system with the rest of the grid. To avoid power swings while synchronising, the phase angle difference should be minimal preferably around 20 degrees (or through synchro check relays) and frequency difference as small as 0.1 Hz. K. Restoration of Loads After the units at Vindhyachal and Korba were restored through availing start up power from NR, it is essential to connect as much load as possible from MP and Chattisgarh system to avoid power injection back into NR grid as well as to bring up more generation at these stations. The generation available at VSTPS and KSTPS was not properly utilized. On , neither MP nor Chattisgarh were able to restore loads at a faster rate even though external assistance is available. This is mainly due to none availability of load at that time and high-voltage problems along the start up paths. [3] One of the main reasons for hunting of black started units on has been the delay in providing loads along the start up path. [4] L. Cold load pick up : Cold load pick up at times leads to tripping of blackstarted units as well as lines/transformers restored. The generator under frequency trip settings at 47.5 Hz. (instantaneous) are also a concern in case of large frequency variations during load restoration (cold load pick up). On at 0613 hrs. a disturbance occurred in Western Maharashtra System which led to splitting of Western Region into two parts one part comprising loads of Southern Maharashtra along with 187

7 POWER MAP OF WESTERN REGION To Kankroli RAJASTHAN To R.P.Sagar TO KOTA Pichhore TO Motak Zerda (Kansari) Neemuch Satna Bansagar TO SINGRAULI STPS(N.R.) Akrimota Rajghat GUJARAT Palanpur Deodhar Tharad Gandhisagar Bina( PG) Rewa Sankhari Sasan 2 x 250 MW Panendro Vijapur Maihar Ranchodpura Kheralu Bina JHARKHAND Damoh Mehsana Vindhyachal STPS To Rihand Kymore Morwa Anjar Nakhatrana Nardipur(Soja) Jamla Himmatnagar Agar Dhrarngadhra Dehgam MADHYA PRADESH Katni Chhatral Dhansura Suwasra Waidhan NanikhakarMundra Viramgam Ratlam Nagda Morbi Sujalpur Kadana Ujjain Bhopal Jabalpur Birsinghpur Gandhinagar 4 Wanakbori Kotma Godhra Manendragarh Naghedi Wankaner Karamsad 5 Halol Dewas Pithampur Amarkantak Vishramgarh Limbdi Indore Itarsi Jabalupr (PG) Khambolia Sikka Jamnagar Dhuvaran Kasor Asoj Bargi Hasdeo Bango Reliance Bhatia Ranavav Gondal Paliad SARDAR SAROVAR Wagodia Jambuva Indira Sagar Narsinghpur Dhanduka Seoni Korba (E) Ranchi Rajkot Amreli GPEC Rajgarh Burwaha Korba(W) Vartej Jhanor 2 Julwania 1 Khandwa KSTPS Budhipadar Palithane 6 Satpura Chhindwara Pench Balaghat Jetpur Halderwa Savarkundla Kakrapar Nepanagar Khapaswami Sipat ROURKELA Gujarat Utran Bhatapara Keshod Dhokadwa Ichhapur Ukai(H) Pandurna Raigarh 1 Achhalia Kawas 3 Kanhan Una Kalmeshwar 2 Zagadia GSEG KORADI BHILAI Kodinar Ukai(T) Bhusawal Bhandara Essar Navsari Vav Jalgaon Amravati 3 Kim Sachin Malkapur Paras Ambazari RAIPUR 4 Ranasan Diu(D&D) Butibori Khaparkheda Dongargarh Badnera 5 Kapadwanj Magarwada Bhilad Ambheta Urla Vapi Malegaon EldabadAkola ORISSA Yawatmal 6 Mangrol (D & D) Dhule Bhugaon Chalisagaon (Surat LPP) Karadpada MAHARASHTRA Wardha Warora Nasik Bhadravati (DNH) Tarapur Manmad CHHATTISGARH Aurangabad Pusad Dahanu(BSES) Boisar Bhiwand i Jalna CHANDRAPUR Navi Mumbai Maharashtra Borivali Bableshwar Kalwa Nanded 2 x 500 MW 1 Jejuri Trombay Pune( PG) Parbhani 2 Theur Bosari Ahmadnagar BARSOOR Apta Beed 3 Parvati Uran Chinchwad Lonikhand Parli( PG) TO RAMAGUNDAM Nagothane 2 Kandalgaon 3 1 Parli Baramati Latur Udgir Lonand Osmanabad Ujani ANDHRA PRADESH Sholapur(PG) Koyna Sholapur TO L. SILERU New Koyna Q/c Karad Vita L E G E N D Dabhol HYDRO POWER STATIONS Miraj Kolhapur THERMAL - COAL GAS KARNATAKA Gadinglez NUCLEAR POWER STATION 400 KV TRANSMISSION LINES Tillari To Belgaum 400 KV LINES UNDER PLAN UPTO MAR kV HVDC Bipole Prepared by : Mapusa Ponda To Nagjhari GOA 765 kv LINE OS, WRLDC, Mumbai A R A B I A N S E A Kharghar Padghe To Sawai Madhopur NR Shivpuri Kalan Koyna & Parli Power Stations and a second part comprising rest of the grid. The first part collapsed. The restoration of the grid was achieved by 0700 hrs. and the load restoration was in progress. As the morning peak approached, unusual heavy load was incident on the system leading to severe voltage dips and load encroachment of distance relays. Number of 400kV lines tripped which led to a major disturbance splitting the Western Regional Grid into five parts. Normally, the cold load pick up would be a serious problem incase loads are restored within 10 to 15 minutes of the disturbance. M. Protection and Substation equipment The following are the typical problems faced Sometimes provision of bus coupler/line synchro check facilities at important substations are not available. Problems in closing the breaker due to low gas/air pressure. Identification of suspected faulty equipment can be done using both relay indications and physical observations. Control high-voltage during restoration to avoid damage of LAs/CVTs etc. The generator under frequency trip settings at 47.5 Hz. (instantaneous) and over frequency settings at Hz are also a concern in case of large frequency variations during load restoration. Operation of Over-Fluxing relays, Over Voltage (O/V) relay. On , considerable delays experienced while providing start up power to Nasik, and extending supplies from Jhanor Power station due to breaker problems. All the line sections involved in start up power transmission should Motijheel Agra Mehgaon Malanpur Gwalior TO Auraiya UTTAR PRADESH Fig. 1. POWER MAP OF WESTERN REGION, INDIA Web Link : have properly maintained breakers to avoid delays. Another significant problem would be the condition of DC batteries due to inadequate charging which may effect communication and relay operations. N. Effect of Wind generation During restoration,small islands with wind generation may have to encounter sudden and large frequency changes due to starting or stopping of wind generators. It is advisable to disallow wind generation during restoration until partsystems or islands attain adequate stiffness. IV. CONCLUSION The problems during restoration could be minimized with proper planning and some of these are listed below. The restoration problems to be considered while planning of the grids, which is not being done presently. Voltage control along various start-up paths. This includes studies for requirement of reactors, various Flexible AC transmission (FACT) devices and identification of suitable nodes. Deployment of synchro-check relays and other means to avoid paralleling of different supplies. Expert systems to aid operators during restoration. Expert systems to identify faulty equipment. Expert systems for processing alarms in SCADA system. Commercial means to maintain grid discipline during grid restoration. Periodic conduction of Blackstart workshops and mock drills in the region. ACKNOWLEDGMENT The authors acknowledge with thanks the guidance and support given by the management of POWERGRID and for permitting the publication of this paper. The views expressed in this paper are of the authors in their individual capacity and not necessarily that of Power grid Corporation of India Ltd. REFERENCES [1] Recovery procedures for western region Aug Issued by WRLDC, file available at web link [2] M. Adibi(chairman),P.clellard, L.Fink, H.Happ, R.Kafka, J. Raine, D.Scheurer, F. Trefny Power System Restoration A Task Force Report [3] Anjan Roy,V.K veluchamy,p.pentayya,r.k.mediratta,pushpa.s,haresh Patel Restoration of Western Regional Grid A Case Study of Presented at the National seminar on Grid operation and Management organized by Central board of Irrigation & Power at Chennai on 29 th & 30 th October 2002 [4] Anjan Roy, V.K.Veluchamy, P.Pentayya, R.K. Mediratta, Pushpa S, Haresh Patel Restoration of western regional grid A case study of , Presented at the workshop for load dispatch personnel and system operators at WREB, Mumbai on 27/09/