Report on the Grid Disturbance on 30th July 2012 and Grid Disturbance on 31st July 2012

Submitted in Compliance to CERC Order in Petition No. 167/Suo-Motu/2012 dated 1st Aug 2012

8th August 2012

CHAPTER 1 – EXECUTIVE SUMMARY

The All India demand met is of the order of 110,000 MW currently. The synchronously connected NEW Grid comprising of the Northern, Western, Eastern and North-Eastern Grids is meeting a demand of about 75,000 to 80,000 MW. The Southern Grid which is connected to NEW Grid asynchronously, is the meeting a demand of about 30,000 MW. The generation resources, primarily coal, are located in the Eastern part of the country, hydro in the north and north-east and the major load centers are located in the North, West and South parts of the country. The backbone of the transmission grid is formed by the 400 kV transmission system and the upcoming 765 kV lines.

There have been major grid disturbances on the 30th and the 31st July 2012 which have affected large parts of the Indian Electricity Grids. Due to high load and failure of monsoon, Northern Region was drawing a large quantum of power from neighboring Western and Eastern Grids whereas due to rains in Western Region demand was less and it was under-drawing. This situation led to a much skewed load generation balance among the regions. A large quantum of power was flowing from the Western Grid to the Northern Grid directly as well as through the Eastern Grid and the system was under stress. Briefly, the details of the grid disturbances on the two days are given below.

1.1 Grid Disturbance on 30th July 2012

A disturbance occurred in the Northern India electricity grid at 0233 hours of 30th July 2012 leading to a blackout in nearly the entire Northern region covering all the 8 States i.e., the States of Delhi, Uttar Pradesh, Uttarakhand, Rajasthan, Punjab, Haryana, Himachal Pradesh and Jammu and Kashmir as well as the Union Territory of Chandigarh. The frequency just before the incident was 49.68 Hz. The All India Demand Met prior to the incident was about 99700 MW and the demand being met in the Northern Region was about 38000 MW.

Small pockets of generation and loads in the Northern Region survived the blackout which comprised of 3 generating units at Badarpur thermal power station with approximately 250 MW load in Delhi, Narora Atomic Power Station in UP on house load some parts of Rajasthan system (around Bhinmal) that remained connected to the Western Grid with a load of about 100 MW and some parts of Uttar Pradesh system (around Sahupuri) that remained connected with Eastern region. Some load of Western Region (around Gwalior area) remained connected to NR via 400 kV Gwalior-Agra-I.

Immediately after the disturbance, restoration of the affected areas was taken up. Startup supply was extended to the thermal power stations and essential loads by taking assistance from the neighboring Eastern and the Western Grids. Hydro generation was self started at Uri and Salal in J & K; Chamera-1, Nathpa Jhakri, Karcham Wangtoo, Bhakra and Pong in Himachal Pradesh; and Chibro/Khodri HEP in Uttarakhand.

Supply was extended to all emergency loads such as Railways, Metros and airport mostly by about 0800 hours. By 1000 hours of 30th July 2012, nearly 40% of the antecedent load (more than 15000 MW) had been restored covering most of the towns and all thermal power stations were extended start up supply. The Northern Regional System was fully restored by 1600 Hrs.

1.2 Grid Disturbance on 31st July 2012

Another disturbance that occurred at 1300 hours of 31st July 2012 affected the Northern, Eastern and North-Eastern electricity grids. The frequency before the incident was 49.84 Hz. The All India Demand Met just prior to the incident was about 100,500 MW and the demand being met in the NEW Grid was 73000 MW approximately.

Approximately 48000 MW of consumer load across 21 States and 1 Union Territory was affected by the grid disturbance. The areas which survived included Western Region, generating units at Narora Atomic Power Station, Anta GPS, Dadri GPS and Faridabad GPS as well as part of Delhi system in NR and system comprising of Sterlite/IB TPS, Bokaro Steel and CESC Kolkata systems in ER.

Immediate steps were initiated for restoration of the areas affected in the incident. Start up supply was extended from the Western Region and the Southern Region which were intact. Several hydro units in the Northern Region, Eastern Region and North-Eastern Region were self started. Supply was extended to emergency loads such as Railways, Metro, Mines and Airports, etc. All emergency loads such as Railways, Metros and airport were provided with power supply mostly by about 1530 hours approximately. The system was restored fully by about 2130 hrs of 31st July 2012.

1.3 Direction of the Hon’ble Commission Vide Petition No. 167/Suo Moto/2012

Central Electricity Regulatory Commission (CERC) vide Petition No. 167/Suo Moto/2012 dated 1st August 2012 (copy enclosed as Exhibit – 1) has given a direction to investigate into the incidences of grid failure on 30th July 2012 and 31st July 2012 and submit a report within a week from the date of issue of the order. The Hon’ble Commission has directed that the report shall include the following:

a) Antecedent conditions of frequency b) Inter-regional/inter-State line flow c) Voltages at inter-State/inter-regional point d) Conditions of outage at inter-regional/inter-State lines prior to disturbance e) Report of the Sequence of Event recorder maintained by RLDCs f) Disturbance recorder reports and any other associated reports.

1.4 Preliminary Report on the Grid Disturbances on 30th July 2012 and 31st July 2012 to the Hon’ble Commission

This preliminary report is being submitted in compliance to the Hon’ble Commission’s directive in Petition No. 167/Suo Moto/2012 dated 1st August 2012 as mentioned above. The organization of the Report is briefly given below.

Chapter – 2 describes the antecedent conditions prevailing in the grid on the 30th July 2012 which includes the frequency profile, important line flows including inter-regional/inter-state line flows, voltages at important nodes and line outages just prior to the grid disturbance. This section also speaks of the messages issued by NLDC/RLDCs in the context of the prevailing conditions.

Chapter – 3 gives the preliminary analysis of the grid disturbance on the 30th July 2012 and includes the analysis of the contingency situations, Sequence of Events, outputs of the disturbance recorders and other reports received from the substations.

Chapter – 4 describes the restoration process undertaken on the 30th July 2012 after the grid disturbance. Startup supply was availed from the Western Region and the Eastern Region which were intact. It mentions the extension of supply to essential loads such Railways, Metro, etc., extension of supply to thermal power stations, self-start by hydro units and the build-up of the NR System.

Chapter – 5 describes the antecedent conditions prevailing in the grid on the 31st July 2012 which includes the frequency profile, important line flows including inter-regional/inter-state line flows, voltages at important nodes and line outages just prior to the grid disturbance. This section also speaks of the messages issued by NLDC/RLDCs in the context of the prevailing conditions.

Chapter – 6 gives the preliminary analysis of the grid disturbance on the 31st July 2012 and includes the analysis of the contingency situations, Sequence of Events, outputs of the disturbance recorders and other reports received from the substations.

Chapter – 7 describes the restoration process undertaken on the 31st July 2012 after the grid disturbance. Startup supply was availed from the Western Region and the Southern Region which were intact. It mentions the extension of supply to essential loads such Railways, Metro, Mines, etc., extension of supply to thermal power stations, self-start by hydro units and the build-up of the Northern, Eastern and the North-Eastern Grids.

Chapter – 8 discusses the status of communication and telemetry facilities available at the RLDCs/NLDC including data availability before and after the grid disturbance. It mentions the impact of the non-availability of the data and deliberates on the urgent need for coordinated planning and implementation of communication infrastructure in the power sector.

Chapter – 9 analyzes the disturbances from various view points and in different perspectives. The underlying causes and the suggested measures to reduce the probability of re-occurrence of such grid disturbances are discussed. A number of issues have been thrown up by the recent grid disturbances and these include the following:

a) Skewed load generation balance across Regional grids b) Grid indiscipline including overdrawals and under drawals c) Depleted reliability margins d) Failure of defense mechanisms e) Absence of primary response from generators f) Insufficient visibility and situational awareness at Load Despatch Centers g) Inadequate appreciation of transfer capability vis-à-vis transmission capacity h) Inadequate dynamic reactive reserves i) Performance of the Protection Systems j) Impediments to the speedy restoration of the systems k) Distortions arising from the existing Regulations on grant of connectivity l) Excessive reliance on unscheduled interchange rather than organized electricity markets m) Tightening of the stipulated range for grid frequency n) Institutional issues

The chapter also deliberates on the actions taken after the occurrence of the disturbances. These are critical issues which have come to the fore and which need attention in the context of grid disturbances on 30th and 31st July 2012. Course correction is required in all time horizons right from long term measures, medium term measures and immediate actions to be taken.

1.5 Enquiry Committee Constituted by Ministry of Power, Govt. of India

Ministry of Power, Government of India vide OM No. 17/1/2012-OM dated 3rd August 2012 has constituted a Committee under the Chairmanship of Chairperson CEA having independent members to enquire into the Grid Disturbances on the 30th and 31st July 2012. Further, POWERGRID and POSOCO have been directed to assist the Committee.

In view of above, a copy of this preliminary report is also being made available to the Committee set up by the Ministry of Power, Government of India in compliance to the directions given by the Government.

CHAPTER 3 – ANALYSIS OF THE DISTURBANCE ON 30TH JULY 2012 (concluding analysis)

It has to be appreciated that in an integrated and meshed system, a 10 MW reduction on 220 kV Badod-Kota line would require at least 100 MW load shedding in Northern Region and similar backing down of generation in Western region. This calls for a fast response time from all the SLDCs and power stations.

As seen from the above sequence, this tripping is essentially a Zone-3 tripping on load encroachment. These settings need to be examined separately. In the past such relay surprises when the system was stressed have led to blackouts on 12th October 2007 in Northern Grid, 2nd January 2010 in Northern Grid (twice) and on 18th November 2010 in Mumbai system.

After the tripping of 400 kV Bina-Gwalior-1, the system has collapsed within seconds and beyond the control of the operator. After this line has tripped a number of lines have tripped on distance protection either due to load encroachment or power swing. In many cases only one out of the two distance protection scheme has sensed the load encroachment and tripped the line. For a heavily stressed or loaded system, dynamic reactive power consumption at both ends of the line is essential to compensate the additional reactive power consumed by the line. This was possibly not adequate. A clear picture can emerge only after observing the Data Acquisition System (DAS) outputs from the different power plants and whether the generators reached their over-excitation limit during this event.

The East to North ties tripped leading to separation of Northern region. Six East to North ties which were in service were high capacity Quad Moose conductors, two of which had FSC and TCSC also. Separation on such a high capacity multiple circuit corridor due to load encroachment/power swing is again an issue which needs to be examined.

The Northern Region after separation of the NEW grid should ideally have survived due to Under Frequency Relay (UFR) and df/dt relay load-shedding. That the frequency could not stabilize is a matter of concern needs a detailed investigation separately.

In rest of the NEW grid also, the frequency rose to 50.92 Hz and tripping of seventeen 400 kV lines on high voltage and nine generating units due to various reasons is also a matter of concern as secondary disturbances could have taken place in this system also. It again illustrates the absence of primary response from the generating units and lack of dynamic reactive resources.

CHAPTER 6 – ANALYSIS OF THE DISTURBANCE ON 31ST JULY 2012 (concluding analysis)

It has to be appreciated that in an integrated and meshed system, a 10 MW reduction on 220 kV Badod-Kota line would require at least 100 MW load shedding in Northern Region and similar backing down of generation in Western region. This calls for a fast response time from all the SLDCs and power stations.

At 1250 hours, tripping of Suratgarh unit 1 in Rajasthan led to further transfers between Western Region and Northern Region. However even before the flow could be controlled, the 220 kV MP to Rajasthan D/C lines, 400 kV Gwalior-Bina-1 and 220 kV Bina-Gwalior D/C tripped within four minutes span. This was effectively a N-G-3 contingency as far as the system was concerned. It is stated that the transmission system is not planned and operated for a N-G-3 contingency. A part of MP load also got incident on Northern region after these trippings further stressing the network in Eastern Region when the West to North ties snapped.

As seen from the above sequence, the tripping of 400 kV Bina-Gwalior-1 appears to be a case of Zone-3 distance protection acting due to load encroachment. These settings need to be examined separately. In the past such relay surprises when the system was stressed have led to blackouts on 12th October 2007 in Northern Grid, 2nd January 2010 in Northern Grid (twice) and on 18th November 2010 in Mumbai system.

After the tripping of 400 kV Bina-Gwalior-1, the system has collapsed within seconds and beyond the control of the operator. The power flowing from West to North took a longer path via Eastern Region. Here the following circuits were out either due to equipment problem and/or voltage control:

• 400 kV Sipat-Ranchi-1 due to isolator problem at Sipat end
• 400 kV Rourkela-Jamshedpur-2 due to Lightning Arrestor (LA) problem at Rourkela
• 400 kV Ranchi-Maithon RB-2 due to tower damage
• 400 kV Ranchi-Maithon RB-1 due to high voltage

Many transmission lines tripped on load encroachment/power swing with only one out of the two distance protection scheme detecting the swing and tripping the lines leading to system separation. The relay behaviour under different load conditions needs to be studied separately. Heavy loading on transmission lines necessitates reactive power support from the generators at both ends of the line. This aspect is generally not factored in appropriately. This had led to Eastern Region experiencing a sudden dip in voltage due to wheeling of power to Northern Region even though the antecedent voltages were much above the nominal. A clear picture can emerge only after observing the Data Acquisition System (DAS) outputs from the different power plants and whether the generators reached their over-excitation limit during this event.

The Northern-Eastern and North Eastern regions after separation from the NEW grid should ideally have survived due to Under Frequency Relay (UFR) and df/dt relay load-shedding. In fact the frequency stabilized at 48.12 Hz for nearly a minute before it collapsed. The UFR load-shedding was not adequate to bring the frequency back to a safer level of 49.5 Hz and above. Any unit tripping at 48.12 Hz and/or onset of load could have caused the frequency to decline below 47.5 Hz where most of the generators trip out leading to a collapse. This is a matter of concern and needs to be examined separately.

In the Western Region also the frequency rose to 51.4 Hz and four generating units and five 400 kV lines tripped. The frequency rise to this level indicates the absence of primary response from generating units.

CHAPTER 8 – STATUS OF COMMUNICATION AND TELEMETRY

8.1 Communication System for Data and Voice

Wide Band Communication systems consisting of Fibre Optic System for facilitating operation of power system has been established for all the regions of the country. Some of the RTUs use Power Line Carrier Communication (PLCC) data transfer from RTU locations to the nearest wideband/control centre locations. The requirement of Communication system for Power system operation and maintenance has increased with the advent of Special protection Schemes, PMU, Wide Area Measurement Technology and requirement for Remote Operation.

The backbone communication network is being provided and maintained by CTU which is primarily based on fiber optic communication. The last mile connectivity is being provided by PLCC communication. Apart from the above, other communication media such as VSAT, GPRS, and leased lines are also being used.

Availability of communication system is essential for data availability at the Control Center. Further, voice communication is also essential. The reliability of data transmission to the RLDCs depends on the availability of redundant channel and the route diversity provided in the communication network. The route diversity ensures availability of data in case of outage of wideband route. Redundant communication channels are needed as failure of the single communication channel leads to data interruption to the RLDCs. However, in the present setup a number of RTUs are integrated through single link.

During the period of the grid disturbance, data from some of the RTUs became non-current for reasons attributable to communication failure after the grid disturbance.

8.2 Power System Visualization and Situational Awareness

Visualization tools and techniques provide the vital inputs to the operator for assessment of the situation and taking remedial measures. The focus is on identification and resolution of the problem with speed and accuracy. Data converted into information must be presented to the operator in a meaningful way, which facilitates easy comprehension, assimilation of the existing situation and facilitates quick response. It is in an emergency or contingent situation that the real importance of the visualization tools is felt as compared to the peacetime scenario.

The RLDCs and NLDC are provided with SCADA systems which have a hierarchical structure of reporting from the RTUs to the Control Center i.e., RTU – Sub-LDCs – SLDCs – RLDCs – NLDC. RTUs installed at CTU substations report directly to the concerned RLDC. The users (Transcos, Gencos including IPPs/MPP, state utilities and others) are responsible for provision of data and voice communication for their respective areas of responsibility.

It may also be appreciated that the Indian Electricity Grids have become large interconnection and the System Operator in the Control Center needs appropriate tools in real time to perform the dispatch functions effectively. Non-availability of the SCADA data including absence of status data also results in the operator’s inability to run tools such as the State Estimator, Contingency Analysis and other tools which are designed to assist him the operation of the grid. It is pertinent to mention here that given the large percentage of data which is not available to the System operator, none of the above mentioned tools give satisfactory results.

8.3 SCADA Data Availability at Control Centres (NLDC/RLDCs) on 30th July and 31st July 2012

Non-availability of the SCADA data leads to incomplete visualization and situational awareness for the system in the control center. Further, at the time of restoration, this also results in delays in the restoration process. (Detailed data availability tables are provided in the full report as Exhibit 8.)

8.4 Data Availability from PMUs in NR and WR

Nine PMUs are installed in the Northern Region, three PMUs are installed in Western Region and three PMUs are installed in Southern Region. Data from all PMUs was available except from Vindhyachal and Agra, where PMU data was not received at NRLDC due to communication issues.

In the near future, more and more PMUs would get installed and communication would be a key to ensure data availability at the Control Center.

8.5 Expanding Grids and Urgent Need for Coordinated Planning and Implementation of Communication Infrastructure

The power system is expanding at a fast rate and new generation and transmission infrastructure is being commissioned. Further, with the restructuring of the power sector many new entities are entering the arena specially a large number of private sector participants. Visualization and analysis of the results of advanced applications such as Contingency Analysis, Optimal Power Flow, etc. is extremely important considering the large volume of data. As the complexity and the size of the power system continue to grow, it would be necessary to adopt advanced visualization tools and techniques to visualize the large amount of power system data.

As per Para 4.6.2 of IEGC 2010, the associated communication system to facilitate data flow up to appropriate data collection point on CTU’s system shall also be established by the concerned user or STU as specified by CTU in the connection agreement. Many stations are coming up without putting in place proper voice and data communication infrastructure.

There is also a need for a comprehensive institutional mechanism regarding planning, implementation, up-gradation, operation & maintenance, resource & cost sharing of a high capacity, fast & reliable communication system for power sector. In view of fast technological advancements in communication, the life of the equipment is less, particularly in terms of spares and services availability.

Considering the difficulties being faced in visualization of the power system and the usage of the SCADA/EMS tools, all the RLDCs have filed petitions before CERC form time to time seeking directions to the users to provide telemetry to the RLDCs for visualization of the Power System.

CHAPTER 9 – SUBMISSION

9.1 Two consecutive Grid Disturbances that occurred on 30th and 31st July 2012 affected the power supply across large parts of the Northern, Eastern and North eastern grid in India. The underlying causes and the suggested measures to avoid its re-occurrence are discussed below:

9.2 Skewed load generation balance across the regional grids

The load generation scenario in the synchronous Northeast-East-West-North (NEW) grid was highly skewed in the month of July. There was spurt in agricultural/weather beating demand in Northern Region (NR) on account of failure of South West monsoon, large gap between requirement and availability on account of high demand growth and aspiration to meet more customer load. On the other hand there was surplus condition in the Western Region (WR) due to high generation availability and heavy under drawal by the constituents of WR. This unscheduled interchange resulted in heavy power flow towards the Northern region from Western and Eastern Region in the antecedent conditions. The large quantum of power flow from WR to ER in real-time was opposite to the power flow from ER to WR envisaged in planning time horizon.

In order to address the above, adequacy norms for regional as well as State control area for all scenarios are important to reduce the security threat arising from such skewed dispatch scenario.

9.3 Grid indiscipline

The Regulations allow deviations from the schedule as long as the operating parameters are within the prescribed standards. There have been occasions when the utilities have continued to overdraw/under inject even at low frequency or over generate/under draw at high frequency. The various instances of grid indiscipline in the form of non-compliance of various provisions of the IEGC and the directions of RLDCs have been brought to the notice of the Hon’ble CERC in the form of petitions. The Hon’ble Commission has imposed penalties in large number of case. Yet the problem of grid indiscipline continues to be a large concern.

The underdrawal/over injection by the Western Region constituents and the over drawal by the Northern Region constituents continued despite several appeals and directions to restrict the deviation from schedule by the utilities indulging in grid indiscipline. Thus grid indiscipline was a major cause for both the grid disturbances.

Grid discipline is of paramount importance and needs to be adhered to by all Users.

9.4 Depleted reliability margins

In a large system random tripping of one or more elements may occur dynamically. The reduction in the available reliability margins due to the contingencies are difficult to assess and it may take some time to recoup it by suitable generation re dispatch/load shedding.

On 30th July, 400 kV Bina-Gwalior-Agra-II was under planned shutdown, while 400 kV Zerda-Kankroli was taken under emergency shutdown. On 31st July also 400 kV Bina-Gwalior-Agra-II was under planned shutdown, and subsequently 400 kV Zerda-Kankroli and Zerda-Bhinmal went under forced outage. This resulted in significant reduction in reliability margins.

The NEW grid is a large meshed network of around 150 GW installed capacity and it is proposed to be synchronised with the Southern Regional grid of around 50 GW installed capacity in the near future. In a small system, the impact of outage/contingencies is limited to a small area. As per provision of Clause 4(j) of NLDC Rules, NLDC has been giving feedback to planners at regular intervals. In the feedback dated 14.7.2011, it had been suggested to follow n-1-1 criteria instead of n-1 criteria followed now.

Thus in fast developing large system, N-G-1/N-1-1 contingency criteria may be considered to secure the system even under extreme dispatch.

9.5 Failure of Defense mechanisms

In both the grid disturbances, failure of defence mechanisms/safety net in the form of load shedding schemes through Under Frequency Relays, Rate of change of frequency relays and islanding schemes in the Northern and Eastern Region were observed. The approved self-healing mechanisms in the form of System Protection Schemes envisaged to take care of the contingency of 400 kV Gwalior-Agra was yet to be implemented.

These defense mechanisms are extremely important and need to be provided at all strategic locations.

9.6 Absence of Primary Response from generators

During the grid disturbance on 30th July 2012, the frequency in the 41 GW of the combined Western/Eastern/North-eastern grid that separated from the Northern Region increased to 50.95 Hz. Similarly during the grid disturbance on 31st July 2012, the frequency of the 28 GW of the Western Region rose to 51.4 Hz. Thus the absence of the primary response from the generators was evident in both the grid disturbances. On both the days any further rise in frequency could have caused blackout due to cascade tripping of generators even in the areas that survived.

Therefore the mandatory primary response by the generators needs to be enforced urgently.

9.7 Insufficient visibility and situational awareness at the Load Despatch Centres

Visualization and situational awareness at the Load Despatch Centres in the antecedent condition as well as during restoration was severely constrained owing to non-availability of real time data at the Load Despatch Centres from a large number of locations. The State Estimator and other EMS applications such as contingency evaluation etc. also could not be run due to SCADA related deficiencies. The respective Regional Load Despatch Centres have filed petition before the Hon’ble CERC for maintaining the data telemetry and communication facilities in line with the Indian Electricity Grid Code, Grid Standards and other Regulations issued by the Commission and the efforts towards upgradation of the existing SCADA/EMS systems are underway. Similarly efforts are being made to provide wide area visibility along with the associated applications at the Load Despatch Centre with the help of Phasor Measurement Unit (PMU) based Synchrophasor technology.

Further thrust is required to enhance the visibility and situational awareness at all levels.

9.8 Inadequate appreciation of Transfer Capability vis-a-vis transmission capacity

Ever since the formation of the synchronous NEW grid in August 2003, concerns have been expressed by most of the stakeholders regarding the difference in the transfer capability vis-a-vis the transmission capacity and the legitimacy of reliability margins. The process of transfer capability assessment helps in envisaging the transmission constraints for the scheduled power flows in the operating time horizon. However the constraints arising from the Unscheduled Interchanges are difficult to forecast and foresee.

As a part of the assessment of transfer capability the operating limits of the various transmission facilities are computed by RLDCs/NLDC and compared with the power flows arising from the anticipated scenario. Requests for scheduling Open Access transactions at the inter-State level are approved only if there are margins in the system. Similar mechanisms are required to be in place at the planning as well as at intra State level by the SLDCs as per the procedures. During the antecedent conditions of both the grid disturbances, the loading of transmission lines was below the thermal limit.

The operators were concerned on increase in the loading of the WR-NR inter regional link owing to the depleting transmission and large unscheduled interchange by utilities. Congestion charge for alleviation of congestion in real time could have been invoked but for the limiting provisions in para 5.4 of the Procedure for Relieving Congestion in Real Time Operations. Therefore as per the regulation 6.4.12 in case of overloading of lines, the NLDC/RLDCs were giving directions to curtail deviations from schedule. However even as the collective actions taken for curtailment of the overdrawl in the Northern Region and reduction of injection in the Western Region were being taken, multiple contingencies occurred in a short span of time.

In a large system, the adequate appreciation of the transfer capability is essential at all control centres.

9.9 Inadequate Dynamic Reactive Reserves

When lines operate beyond surge impedance loading, reactive power is consumed by the line and voltage drops. High MW flow, coupled with MVAR loss/flow in the line, leads to low voltage and high current. This may cause load encroachment in the relays, i.e. normal load may be seen as fault and tripping of lines would be a surprise in real-time operation. On both the occasions, i.e. on 30th and 31st July 2012, there was high loading on WR-NR corridor, especially 400 kV Bina-Gwalior, which was carrying more than SIL rating and this led to low voltages at the Gwalior end in the event of high line loading.

Dynamic reserve can be provided by generators or SVCs. At present only 2 SVCs of +140 MVAR capacity are available at Kanpur substation. In order to take care of contingencies like fault, high line loading, large load throw-off, dynamic reactive reserve is required at strategic locations in the grid. Feedback in this regard had been sent to CEA and CTU by NLDC vide letter dated 24.6.2010.

9.10 Performance of the Protection System

Under stressed network conditions, proper behavior of protective systems installed on transmission lines and generating units are vital. However in actual practice there are instances where settings of relays are corrected/changed with change in the fast expanding network.

However, a thorough audit of protective systems and encompassing all related areas is urgently required.

9.11 Impediments to the Speedy Restoration of Systems

Restoration was taken up post grid disturbance as per the procedures. However difficulties were experienced on account of constraints in extension of start-up supply, difficulties in black start, load generation-imbalance, reactive energy imbalance, failure of built up subsystems/islands, deficiencies in communication, inadequate telemetry and inadequate reactive resources.

Renewed emphasis on mock trial of the contingency plans may be given.

9.12 Distortions arising from existing Regulations for grant of connectivity

The existing provisions in the regulations for (Grant of Connectivity, Long-term Access and Medium-term Open Access in inter-State Transmission and related matters) permitting connectivity to the grid even without identification of beneficiaries at the time of application are resulting in unforeseen power flows across the synchronous grid. This coupled with unrestricted injection/drawal as Unscheduled Interchange (UI) within the IEGC frequency band results in large difference in power flow in real-time as compared to what was envisaged during planning stage and thereby results in critical loading of the transmission that endangers grid security.

Further large capacity dedicated lines built within the meshed system without adequate redundancies could endanger grid security.

The distortions discussed above need to be suitably addressed.

9.13 Excessive reliance on unscheduled interchange rather than organized markets

Unlike power purchase through Short Term Open Access, Medium Term Open Access or Long Term Access, payment can be delayed in case of drawal in the form of Unscheduled Interchange. Though there is provision of Letter of Credit (LC), many of the utilities have not opened LC. As a consequence, some utilities prefer to draw power from the grid in the form of Unscheduled Interchange rather than availing power from organized market through long term, medium term and short term contracts without much consideration to the grid security. Suitable deterrent mechanism needs to be put in place measures to discourage such exploitation of the UI mechanism and bring about financial discipline.

Under the present regulations there is no cap on the volume of Unscheduled Interchange as long as the frequency is within the stipulated operating range. In the antecedent conditions of both the grid disturbances, the efforts to curtail deviations from schedule failed to bring about the desired results probably because the frequency was within the stipulated operating range. Thus the prevailing mechanism of Unscheduled Interchange may be reviewed to address the security concerns emerging from the growth in the size of the synchronous interconnection and the behaviour of the market participants in the existing market design in India.

9.14 Tightening of the stipulated range for Grid Frequency

As per the Clause 5.2(m) of the CERC (Indian Electricity Grid Code) Regulations, 2010 the prevailing stipulated range for grid frequency in India is 49.5-50.2 Hz. In view of the security threats arising from large variation in trans-regional power flow for a small variation in grid frequency the CERC (Indian Electricity Grid Code) (First Amendment) Regulations, 2012 envisaged tightening of the permissible range of frequency to 49.7-50.2 Hz. However, the above Regulation has been stayed by the Hon’ble Madras High Court and is being agitated at the Hon’ble Supreme Court.

The Central Advisory Committee in its 16th meeting held on 14th March 2012 had also opined that the higher range of permissible frequency could be reduced from the existing 50.2 Hz to 50.1 Hz. Thus the permissible range of the operating grid frequency should be narrowed to 49.8 Hz to 50.1 Hz and subsequently tightened to 49.9 Hz to 50.1 Hz with a step of 0.01 Hz prior to the synchronization of Southern Regional grid with NEW grid.

The larger integrated grid has a huge power number, i.e. the change in frequency even for a large change in Load or Generation is small. This situation may lead to dangerously high line loading at far end in case of contingencies like tripping of generating units, as the State utilities operate the grid with limited visibility of the State network and system frequency. This situation may end up with major grid disturbance if the frequency band is wider. Even in the present scenario, some of the critical transmission lines/transformers are loaded to such a level that any incremental loading due to contingencies may lead to cascade tripping. The State utilities continue to draw more just by keeping the minimum mandated frequency level as reference for their demand management.

The narrowing of the frequency band would be a step towards ensuring secure grid operation and quality of power. Most of the large power systems in the world operate at near constant frequency and only very small deviations are allowed. In India, looking into the huge mismatch between generation and demand, more deviation was allowed earlier; especially when grids were not integrated and size was relatively smaller. With regional grid being inter-connected and grid sizes increasing steadily, it is necessary to tighten the frequency band for secure grid operation.

9.15 Institutional issues

Ensuring integrated operation is a collective responsibility. The strengthening of Load Despatch Centres in terms of adequacy and competence of manpower as well as availability of suitable tools would enhance the effectiveness and efficiency of Load Despatch Centres. While several initiative are being taken for empowerment of the Load Despatch Centres, the grid disturbance has emphasized the need for a greater thrust at institutional capacity building of the Load Despatch Centres in India.

9.16 Actions taken after grid disturbances to ensure secure operation

Following actions have been taken up post grid disturbance to ensure secure operation:

1. Special Protection Scheme to shed load in Northern Region in case of loss of injection from Gwalior through 400 kV Agra-Gwalior lines has been implemented.
2. In a meeting taken by Secretary (Power) on 31.7.2012 at NLDC, it was decided that transfer capability of inter-regional links and other critical links would be reviewed in consultation with CEA and CTU and implemented within 24 hours. Accordingly, assessment of Transfer capability based on SIL limits of the lines instead of stability limit evaluated from St Clair’s curve or thermal limit depending on the line length has been implemented and has been uploaded on the website of NLDC.
3. 765 kV Bina-Gwalior-Agra-II (charged at 400 kV), was under shutdown at the time of disturbance. The line has since been restored on 7.8.2012.
4. Extensive audit of protection system has been initiated. List of sub-stations where protection audit is to be undertaken on priority basis has been prepared.
5. Zone-III setting of 400 kV Bina-Gwalior-Agra has been modified to minimize load encroachment in case of low voltage conditions.
6. Utilities/generators are being asked not to deviate from schedule irrespective of system frequency.
7. A meeting of States had been convened by Ministry of Power on 6th August 2012 where the following resolutions were adopted: a. Adequate defense plans and protection system shall be put in place to ensure integrated operation of the National/Regional Grids in adherence with the Indian Electricity Grid Code (IEGC). All the states shall ascertain preparedness of power system defense plans and cooperate at the Regional level for coordinating their Protection systems. b. Defense plans of the states must include islanding schemes, under frequency relays, rate of change of frequency relays, special protection schemes and automatic demand management schemes. The defense plans shall also include restoration procedures that shall be updated and reviewed regularly. c. States will prepare their islanding schemes in consultation with PGCIL, CEA and NRPC within the next 3 months and ensure their implementation within the next 6 months. d. Independent third party audit of the protection systems shall be carried out within 1 month and the Regional Power Committees (RPCs) shall monitor the same. PGCIL would fund and carry out the audit in the first instance. e. All the utilities shall also adopt good operation and maintenance practices and random checks of these shall be carried out by the Regional Power Committees. f. States shall prepare plans in long term, medium term and short term horizons for procurement of power, network and demand management in accordance with the Indian Electricity Grid Code (IEGC), which shall be reviewed by the RPCs. g. States shall carry out periodically Power system studies for operation planning and Transfer Capability determination. PGCIL would assist the states in this regard. h. States shall take all necessary steps for strengthening and upgrading the State Load Despatch Centres and training of system operators. There should be manpower capacity building by way of training and certification. i. The personnel manning the LDC control rooms should be equipped with proper tools to facilitate the discharge of the functions. Appropriate compensation structure, including Certification linked incentive scheme must be designed to attract and retain best talent in the field of system operations. j. The States requested that Government of India may draw up a scheme for supporting the states in strengthening their SLDCs and for capacity building. k. POSOCO would evolve a contingency load shedding protocol, especially when non frequency related load shedding is required. l. All States resolved to adhere to the Indian Electricity Grid Code (IEGC) and take all requisite measures for its effective enforcement. It was agreed that all instructions of NLDC/NRLDC will be implemented immediately by SLDCs without waiting for further instructions from any other authority.

Note: this file contains the executive summary, the concluding analytical sections of Chapters 3 and 6, and the full text of Chapters 8 and 9 of the 129-page report. The remaining chapters (2, 4, 5, 7) consist primarily of detailed antecedent-condition data tables, sequence-of-event tables, and station-by-station restoration timestamp tables that have been omitted here for length; they are available in the original PDF.