报告详细：
REPORT OF THE ENQUIRY COMMITTEE
ON
GRID DISTURBANCE
IN NORTHERN REGION
ON 30th July 2012
AND
IN NORTHERN, EASTERN & NORTH-EASTERN REGION
ON 31st JULY 2012
16th AUGUST 2012
NEW DELHI
ACKNOWLEDGEMENT
The committee gratefully acknowledges the efforts put in by all assisting members to the enquiry committee namely :
a. Shri R. N. Nayak, CMD, POWERGRID
b. Shri S. K. Soonee, CEO, POSOCO
c. Shri Balvinder Singh, IPS Retired.
The Committee places on record the efforts of Shri K. K. Agrawal, Member (GO&D), CEA for overall coordination in the whole exercise of grid disturbance enquiry.
The committee also gratefully acknowledges and places on record its appreciation towards the following members of various sub-groups, for their efforts of in-depth analysis and compilation of grid disturbance analysis:
(i) Shri Manjit Singh, Member (Thermal), CEA
(ii) Shri P.K. Pahwa, Member Secretary, NRPC,
(iii) Dr. Anil Kulkarni, IIT-B, Mumbai,
(iv) Shri Ajit Singh, Ex-Addl. Secretary, Cabinet Secretariat
(v) Shri R.K. Verma, Chief Engineer I/c (DP&D), CEA
(vi) Shri Dinesh Chandra, Chief Engineer (I/C), GM Div., CEA
(vii) Shri Ajay Talegaonkar, SE (Operation), NRPC
(viii) Shri S. Satyanarayan, SE (Operation), WRPC,
(ix) Shri D. K. Srivastava, Director, GM Div., CEA
The committee expresses its appreciation of the cooperation extended by POWERGRID and POSOCO, for making the data available from various Sub-Stations/RLDCs.
Last but not the least Committee also acknowledges the efforts of all those persons who gave their valuable support directly or indirectly.
CONTENTS Page No.
Executive Summary iv-ix
Chapter 1: Introduction 1-4
Chapter 2: Overview of the regional grids 5-7
Chapter 3: Analysis of the grid disturbance on 30th July 2012 8-20
Chapter 4: Analysis of grid disturbance on 31st July 2012 21-32
Chapter 5: Factors contributing to grid disturbances on 30th and 31st July 2012 33-39
Chapter 6: Review of islanding schemes 40-44
Chapter7: Review of restoration of generation 45-58
Chapter 8: Cyber security related aspects 59-62
Chapter 9: Recommendations of the Committee 63-70
Supplementary Volume:
A separate volume containing the relevant DR outputs during the grid disturbances on 30th and 31st July, 2012.
GLOSSARY:
ABT: Availability Based Tariff
ATC: Available Transfer Capacity
AUFLS: Automatic Under Frequency Load Shedding
BLU: Boiler Light Up
BTPS: Badarpur Thermal Power Station
CB: Circuit Breaker
CEA: Central Electricity Authority
CERC: Central Electricity Regulatory Commission
CESC: Calcutta Electric Supply Company
CTU: Central Transmission Utility
D/C: Double Circuit
DMRC: Delhi Metro Rail Corporation
DR: Disturbance Recorder
df/dt: Rate of change of frequency with time
EL: Event Logger
ER: Eastern Region
FGMO: Free Governor Mode of Operation
FSC: Fixed Series Compensation
GPS: Gas Power Station
GT: Gas Turbine
HVDC: High Voltage Direct Current
MERC: Maharashtra Electricity Regulatory Commission
NAPS: Narora Atomic Power Station
NER: North-Eastern Region
NR: Northern Region
PMU: Phasor Measurement Unit
PLCC: Power Line Carrier Communication
POSOCO: Power System Operation Corporation Ltd.
POWERGRID Powergrid Corporation of India Ltd
PPA: Power Purchase Agreement
PSS: Power System Stabilizer
RAPP: Rajasthan Atomic Power Plant
RPC: Regional Power Committee
RLDC: Regional Load Despatch Centre
SCADA: Supervisory Control and Data Acquisition System
SIL: Surge Impedance Loading
SR: Southern Region
STOA: Short Term Open Access
SVC: Static VAR Compensator
TTC: Total Transfer Capability
TCSC: Thyristor Controlled Series Compensation
UI: Unscheduled Interchange (under ABT)
VAR: Volt Ampere Reactive
WAFMS: Wide Area Frequency Measurement System
WR: Western Region
EXECUTIVE SUMMARY
There was a major grid disturbance in Northern Region at 02.33 hrs on 30-07-2012. Northern Regional Grid load was about 36,000 MW at the time of disturbance. Subsequently, there was another grid disturbance at 13.00 hrs on 31-07-2012 resulting in collapse of Northern, Eastern and North-Eastern regional grids. The total load of about 48,000 MW was affected in this black out. On both the days, few pockets survived from black out. Ministry of Power constituted an Enquiry Committee, to analyse the causes of these disturbances and to suggest measures to avoid recurrence of such disturbance in future.
The Committee analysed the output of Disturbance Recorders (DR), Event loggers (EL), PMUs, WAFMS, SCADA data and reports submitted by various SLDCs , RLDCs /NLDC, POWERGRID and generation utilities to arrive at the sequence of events leading to the blackouts on 30th July, 2012 and 31st July 2012. The Committee also interacted with POWERGRID and POSOCO on various aspects of these grid disturbances. Some teams also made field visits to sub-stations, generating stations, NRLDC, NLDC, UPSLDC and Haryana SLDC.
The Committee is of the opinion that no single factor was responsible for grid disturbances on 30th and 31st July 2012. After careful analysis of these grid disturbances, the Committee has identified several factors, which led to the collapse of the power systems on both the days, as given below:
Factors that led to the initiation of the Grid Disturbance on 30th July, 2012
a. Weak Inter-regional Corridors due to multiple outages: The system was weakened by multiple outages of transmission lines in the WR-NR interface. Effectively, 400 kV Bina-Gwalior-Agra (one circuit) was the only main AC circuit available between WR-NR interface prior to the grid disturbance.
b. High Loading on 400 kV Bina-Gwalior-Agra link: The overdrawal by some of the NR utilities, utilizing Unscheduled Interchange (UI), contributed to high loading on this tie line.
c. Inadequate response by SLDCs to the instructions of RLDCs to reduce overdrawal by the NR utilities and underdrawal/excess generation by the WR utilities.
d. Loss of 400 kV Bina-Gwalior link: Since the interregional interface was very weak, tripping of 400 kV Bina-Gwalior line on zone-3 protection of distance relay caused the NR system to separate from the WR. This happened due to load encroachment (high loading of line resulting in high line current and low bus voltage). However, there was no fault observed in the system.
Factors that led to the initiation of the Grid Disturbance on 31st July, 2012
(i) Weak Inter-regional Corridors due to multiple outages: The system was weakened by multiple outages of transmission lines in the NR-WR interface and the ER network near the ER-WR interface. On this day also, effectively 400 kV Bina-Gwalior-Agra (one circuit) was the only main circuit available between WR-NR.
(ii) High Loading on 400 kV Bina-Gwalior-Agra link: The overdrwal by NR utilities, utilizing Unscheduled Interchange (UI), contributed to high loading on this tie line. Although real power flow in this line was relatively lower than on 30th July, 2012, the reactive power flow in the line was higher, resulting in lower voltage at Bina end.
(iii) Inadequate Response by SLDCs to RLDCs’ instructions on this day also to reduce overdrawl by the NR utilities and underdrawal by the WR utilities.
(iv) Loss of 400 kV Bina-Gwalior link: Similar to the initiation of the disturbance on 30th July, 2012, tripping of 400 kV Bina-Gwalior line on zone-3 protection of distance relay, due to load encroachment, caused the NR system to separate from the WR system. On this day also the DR records do not show occurrence of any fault in the system.
Brief Sequence of Events leading to the Grid Collapse on 30th and 31st July 2012
(i) On 30th July, 2012, after NR got separated from WR due to tripping of 400 kV Bina-Gwalior line, the NR loads were met through WR-ER-NR route, which caused power swing in the system. Since the center of swing was in the NR-ER interface, the corresponding tie lines tripped, isolating the NR system from the rest of the NEW grid system. The NR grid system collapsed due to under frequency and further power swing within the region.
(ii) On 31st July, 2012, after NR got separated from the WR due to tripping of 400 kV Bina-Gwalior line, the NR loads were met through WR-ER-NR route, which caused power swing in the system. On this day the center of swing was in the ER, near ER-WR interface, and, hence, after tripping of lines in the ER itself, a small part of ER (Ranchi and Rourkela), along with WR, got isolated from the rest of the NEW grid. This caused power swing in the NR-ER interface and resulted in further separation of the NR from the ER+NER system. Subsequently, all the three grids collapsed due to multiple tripping attributed to the internal power swings, under frequency and overvoltage at different places.
(iii) The WR system, however, survived due to tripping of few generators in this region on high frequency on both the days.
(iv)The Southern Region (SR), which was getting power from ER and WR, also survived on 31st July, 2012 with part loads remained fed from the WR and the operation of few defense mechanism, such as AUFLS and HVDC power ramping.
(v) On both the days, no evidence of any cyber attack has been found by the Committee.
Measures that could have saved the system from collapse:
In an emergency system operating condition, such as on 30th and 31st July 2012, even some of the corrective measures out of the list given below might have saved the system from the collapse.
(i) Better coordinated planning of outages of state and regional networks, specifically under depleted condition of the inter-regional power transfer corridors.
(ii) Mandatory activation of primary frequency response of Governors i.e. the generator’s automatic response to adjust its output with variation in the frequency.
(iii) Under-frequency and df/dt based load shedding relief in the utilities’ networks.
(iv) Dynamic security assessment and faster state estimation of the system at load despatch centers for better visualization and planning of the corrective actions.
(v) Adequate reactive power compensation, specifically Dynamic Compensation.
(vi) Better regulation to limit overdrawal/underdrawl under UI mechanism, specifically under insecure operation of the system.
(vii) Measures to avoid mal-operation of protective relays, such as the operation of distance protection under the load encroachment on both the days.
(viii) Deployment of adequate synchrophasor based Wide Area Monitoring System and System Protection Scheme.
Restoration of the system
The Committee observed that on both the days unduly long time was taken by some of the generating units in starting the units after start up power was made available.
Recommendations of the Committee
Detailed recommendations of the committee are given in the main report, which are summarized below.
i) An extensive review and audit of the Protection Systems should be carried out to avoid their undesirable operation.
ii) Frequency Control through Generation reserves/Ancillary services should be adopted, as presently employed UI mechanism is sometimes endangering the grid security. The present UI mechanism needs a review in view of its impact on recent disturbances.
iii) Primary response from generators and operation of defense mechanisms, like Under Frequency & df/dt based load shedding and Special Protection Schemes, should be ensured in accordance with provisions of the grid code so that grid can be saved in case of contingencies.
iv) A review of Total Transfer Capability (TTC) procedure should be carried out , so that it can also be revised under any significant change in system conditions, such as forced outage. This will also allow congestion charges to be applied to relieve the real time congestion.
v) Coordinated outage planning of transmission elements need to be carried out so that depletion of transmission system due to simultaneous outages of several transmission elements could be avoided.
vi) In order to avoid frequent outages/opening of lines under over voltages and also providing voltage support under steady state and dynamic conditions, installation of adequate static and dynamic reactive power compensators should be planned.
vii) Penal provisions of the Electricity Act, 2003 need to be reviewed to ensure better compliance of instructions of Load Desptach Centres and directions of Central Commission.
viii) Available assets, providing system security support such as HVDC, TCSC, SVC controls, should be optimally utilized, so that they provide necessary support in case of contingencies.
ix) Synchrophasor based WAMS should be widely employed across the network to improve the visibility, real time monitoring, protection and control of the system.
x) Load Desptach Centres should be equipped with Dynamic Security Assessment and faster State Estimation tools.
xi) There is need to plan islanding schemes to ensure supply to essential services and faster recovery in case of grid disruptions.
xii) There is need to grant more autonomy to all the Load Despatch Centres so that they can take and implement decisions relating to operation and security of the grid
xiii) To avoid congestion in intra-State transmission system, planning and investment at State level need to be improved.
xiv) Proper telemetry and communication should be ensured to Load Despatch Centres from various transmission elements and generating stations. No new transmission element/generation should be commissioned without the requisite telemetry facilities.
xv) Start up time of generating stations need to be shortened to facilitate faster recovery in case of grid disruptions.
xvi) There is a need to review transmission planning criteria in view of the growing complexity of the system.
xvii) System study groups must be strengthened in various power sector organizations.
xviii) It was also felt that a separate task force may be formed, involving experts from academics, power utilities and system operators, to carry out a detailed analysis of the present grid conditions and anticipated scenarios which might lead to any such disturbances in future. The committee may identify medium and long term corrective measures as well as technological solutions to improve the health of the grid.
