Grid Restoration Challneges and Strategy

Workshop on
RE Integration & System Recovery Procedure
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10-Feb-2017 WRLDC, POSOCO 1

Grid Restoration
Challenges & Strategy

Outline
• Grid Disturbance (6)
• Definition and Category
• Major Blackout in World and Western Regional Grid.
• Restoration (10)
• Restoration Strategy (8)
• Constraint and Challenges During Restoration(7)
• Recent Grid Disturbances- Reason & Challenges in
Restoration(2)
• Prevention of Blackout (10)

Grid Disturbance
Definition and Overview
• Grid Disturbance: Tripping of one or more power system elements of the grid like a
generator, transmission line, transformer, shunt reactor, series capacitor and Static
VAR Compensator, resulting in total failure of supply at a sub-station or loss of
integrity of the grid, at the level of transmission system at 220 kV and above (132 kV
and above in the case of North-Eastern Region)
CEA (Grid Standards) Regulations-2010
• Black Start Procedure: ‘The procedure necessary to recover from a partial or a total
blackout in the region
Indian Electricity Grid Code
“Another aspect of robustness can be illustrated by the fact that a weaker system that has a well
tested plan for emergency procedures and for restoration may be more reliable than a stronger
system with no such plan” : Charles Concordia
Dynamic Performance and Security of Interconnected Systems, IEEE Power Engineering Review,
March 1992.

• Category GD-1 : When less than ten percent of the antecedent generation or load in a Regional
Grid is lost;
• Category GD-2 : When ten per cent to less than twenty percent of the antecedent generation or
load in a regional grid is lost.
• Category GD-3 : When twenty percent to less than thirty percent of the antecedent generation or
load in a regional grid is lost;
• Category GD-4 : When thirty percent to less than forty percent of the antecedent generation or
load in a regional grid is lost;
• Category GD-5 : When forty percent or more of the antecedent generation or load in a regional grid
is lost.
Explanation: For the purpose of categorization of grid disturbances, percentage loss of generation or load,
whichever is higher shall be considered.
Category of Grid Disturbance

Major Power System Blackout
NORTHEAST BLACKOUT USA 1965 NORTHEAST BLACKOUT USA 2003 BRAZIL & PARAGUAY BLACKOUT 2009
INDIAN BLACKOUT 2012
Result of Various Techno-
Economical Issues Merging
Together to Create A
Blackout
Each Blackout Brings
Paradigm Shift in the Power
System Planning and
Operation

Recent Blackouts, GD, Natural Disasters
Blackouts / Grid Disturbance-Recent History
• South Australia: 28th Sep 2016
• Karachi, Pakistan 29th Jan 2016
• Turkey: 30th March 2015
• Pakistan‐25th January 2015
• Bangladesh-1st November 2014
• Indian Grid Blackout- 30th and 31st July 2012
• Southwest Blackout in USA : 8th Sept 2011
• Brazil and Paraguay Blackout: 10-11 Nov 2009
• Italy Blackout : 28 Sept 2003
• Northeast Blackout in USA: 14th Aug 2003.
• Java Bali Blackout : 18 Aug 2005
• Western Regional Grid of India : 30th July 2002
Natural Disasters
• Cyclone Vardhah in Southern India (TN) Dec 2016
• Earth Quake in Nepal: 25‐April‐2015 & 12‐May‐15
• Cyclone Hud (Andhra, Telengana, Odisha): 7-14
Oct 2014
• Flood In Kashmir Valley: 2-25 Sept 2014
• Cyclone Phailin (Odisha, AP) : 4-14 Oct 2013
• Flashflood in Uttarakhand :14-17 June 2013
• Hurricane Sandy: 22-27 October 2012 (United
States)
• Earthquake and Tsunami (Tamilnadu, Thailand):
26 Dec 2004
• Earthquake in Gujarat : 26th Jan 2001
• Super Cyclone-05B in Odisha: 25-Oct-99
• Earthquake in Maharashtra :30 Sept 1993

NO. DATE TIME COLLAPSED PARTS
1 11-10-1988 9:23 Western Madhya Pradesh (MP)
2 28-12-1988 10:34 Western Maharashtra, Part of Gujarat
3 14-08-1989 15:26 Eastern MP
4 17-08-1989 16:35 Western Maharashtra including Mumbai
5 31-07-1990 11:24 MP
6 24-11-1990 8:37 Western Maharashtra and Mumbai
7 16-03-1991 12:43 Western Maharashtra
8 25-10-1991 10:51 Mumbai+Western Maharashtra+Gujarat+Western MP
9 12-02-1992 16:12 South Mumbai + Parts of Western Maharashtra
10 31-03-1992 15:03 Western Maharashtra + Mumbai
11 15-06-1992 19:25 Western MP, Gujarat, Maharashtra and North Mumbai
12 28-05-1993 21:45 Western Maharashtra, Parts of Goa
13 19-04-1995 18:02 Western Maharashtra,Gujarat, North MP and parts of Goa
14 01-05-1995 15:46 Western Maharashtra,Mumbai,North MP and parts of Goa
15 10-11-1995 11:08 Entire Grid except Mumbai and parts of Eastern MP
Major Blackout in Western Region

NO. DATE TIME COLLAPSED PARTS
16 14-11-1995 8:40 Maharashtra system excluding Mumbai
17 09-12-1995 7:36 Entire grid except few islands - Mumbai collapsed
18 11-12-1996 16:02 Western Maharashtra
19 28-02-1997 20:51 Western Maharashtra and Tata Power Company
20 23-10-1997 8:13 Eastern MP including KSTPS and VSTPS
21 26-10-1997 23:55 Maharashtra TPC islanded and survived
22 16-12-1998 10:55 Maharashtra and MP system
23 14-10-2000 4:41 MP system collapsed except Indore area
24 18-05-2002 6:36 Western Maharashtra & Goa
28 30-07-2002 20:11 Entire Western Grid except Mumbai
30 25-02-2007 16:34 Western Maharashtra, North Goa,North Mumbai

Restoration
• Each Blackout is followed by its Restoration.
• Restoration Requires Situational Awareness.
• Restoration requires better documentation, mock drills and training
of operators in advance.
• Restoration requires Essential information dissemination among
Operators.
• Its an Emergency and Operator need to be Calm, Cautious and
Vigilant.

Paradigm Shift
Normal Mode of Operation
Maintain Status Quo
Peace Time Operation
Restoration
Challenging : Change Status Quo
War Time Operation

The objective of Restoration Procedures is to serve as a guideline for achieving
restoration of total system from total blackout in the shortest possible time. The
strategy includes generation securing (i.e., stabilization of saved units), building up
subsystems with the help of generating units having black start capability, extension
of start-up power to thermal and nuclear units, restoration of priority load
(traction, collieries, telecommunications, defense establishments, hospitals),
enlarging the subsystems by synchronization and restoration of other loads.
Objective of Restoration Procedure

Restoration Tasks
• Inform all Emergency Contacts on Event(SoS)
• Don’t Panic …..Be Vigilant…..Check Communication/SCADA Status
• System Status Determination
• Restoration Planning
• Review of Characteristics of the system to be restored
• Plant Preparation services/start-up
• Network Preparation
• Network Energisation
• Load Restoration
• System Rebuilding

Coordination

• Generating stations with capability to black start would commence the black start activities
without waiting for an explicit operation code from SLDC / RLDC.
• Respective SLDC shall coordinate extension of supply from these generating units and build-up of
sub-systems within the State under the overall supervision of WRLDC.
• Operation code shall be taken from SLDC / RLDC for synchronization of two subsystems.
• WRLDC shall coordinate with NLDC / ERLDC / SRLDC / NRLDC for extension of start-up supply from
neighbouring regions and restoration of the Inter State Transmission System.
• The RLDC is authorized during the restoration process following a black out, to operate at
reduced security standards for voltage and frequency as necessary in order to achieve the fastest
possible recovery of the grid.
Know the Codes/Process

Network preparation and Energization
 Clearing all de-energised buses
 Global opening of all the breakers
• Else selective breaker operation after careful consideration
 Sectionalising a system into sub-systems to enable parallel restoration
of islands
 Protection System/Relays
 Choice of feeders
 Switching
 Reactive Compensation

Priority for load build UP
• Start-up power to Hot Thermal units and Nuclear units
• Start-up Power to units that are capable of rapid restart like hydro and gas units
• Supply to Emergency Loads (Such as collieries, telecommunication, Airports, defence
establishment, etc.)
• Supply to Electric Traction
• Supply to Strategic installations / area (District head quarter, Large Event)
Know Your Loads
• Critical power system loads - Loads essential to perform restoration.
• Voltage control - As transmission is energized, load is often required to help keep
voltage within limits.
• Reloading generation - Surviving large thermal generation units on House load (fossil
and nuclear) need to be reloaded as soon as possible after the disturbance, otherwise
the thermal stresses and other physical limitations can slow recovery or prevent them
from recovering. So after the transmission path to these generation units is built, they
must be reloaded as quickly as possible, typically using large blocks of load.

Role of Load Despatch Centre During Restoration
• Determine severity of collapse
• Identify and initiate black start facilities
• Import start-up power from neighboring states/regions
• Decision making and guiding
• Determine priority levels
• Check unbalanced loading due to traction
• Identify points of re-integration and synchronization
• Reporting

Restoration Stages
Load restoration is only a Means to an End
Preparation Actions are
Time Critical
1-2 Hours
3-4 Hours
8-10 Hours
System Restoration Load
Restoration
Load restoration
is the objective

Restoration Strategy
• Recognition of Status of System immediately after collapse
• Stabilization of the System
• Identification of restart sources
• Decision on Initial Restart Strategy
• Need to establish path from restart sources to major generating
units
• Need to initiate system and load restoration as initial major
generating units become available
• Need to move to large scale restoration System Status
Determination

Restoration Strategy-1
Bottom up Approach
Generating stations with black start facilities are to be started Islands formed around
these generating stations by connecting essential loads, followed by reconnection of
these islands at pre-defined locations
• Simultaneous restoration of islands / sub-systems followed by their mutual
synchronization
• Usually selected in case of a complete system collapse and lack of interconnection
assistance
• Requires several operating teams and adequate communication facilities for
mutual coordination

Restoration Strategy-2
Top Down Strategy
Start-up power has to be imported from neighboring regions/surviving systems
and the start up power is required to be extended to all the generating stations
on priority basis while restoring few loads and transformers for voltage control.
• Usually selected when neighbouring interconnection assistance is available
• Interconnection status is to be assessed, hence time consuming and tasking

Identify blacked out areas
Check for islands
Identify the causes; verify equipment availability
Identify sources of available supply
Focus on synchronizing TTH
units with loads
Start restoration in all islands, pick up priority loads and grow
balanced islands
Synchronize all islands
Restore the DC connections last
Buildup Backbone System
from Black start Unit
BottomUpApproach

Strategy Adopted in 30 July 2012 Blackout
Trip to House
Load Units
Hydro and Gas
Black Start Units
Power From Western
region through AC and
HVDC B2B Bypass
Power From Eastern
region through AC Lines
BottomUpApproach
TopDownApproach
Mixed
Approach

Strategy Adopted in 31 July 2012 Blackout
BottomUpApproach
TopDownApproach
Mixed
Approach for
Northern
Region
Trip to House
Load Units
Power From Eastern
region through AC Lines
: Not Available as ER
and NER also Blackout
Hydro and Gas
Black Start Units
Power From Western
region through AC and
HVDC B2B Bypass

BottomUpApproach
TopDownApproach
Mixed
Approach
for Eastern
Region

Bottom Up
Approach in North
Eastern Grid and
Extension of
Supply to ER

Re-assembling Tie elements of power system
Impaired communications, limited information
Non-availability of SCADA/EMS application system
Unfamiliar situation
Time constraints
Constraints During Restoration

Challenges Faced During Restoration
• Repeated failures : The reason for system failure at first place have been unexplained causing
repeated failure on same cause during restoration
• Overvoltage: the consequences can be over-excitation of transformers, generator under-excitation
limitation or even self-excitation, harmonic resonance etc.
• Insufficient knowledge of the system: knowledge of the circumstances of the failure
• Too fast restoration: Attempt to pick-up demand too quickly
• Unavailability of equipment
• Distribution utilities demand : Reconnecting blocks of load bigger than what is possible during
restoration process
• Communications process: Misunderstandings between Control Centres.
Source : VLPGO WG#2 Enhanced Security Report on Best Practices for Electric Power System Restoration

Issues : Active/Reactive/Protective
• Real Power Balance & Control of Frequency
• Radial and Network Loads (Cold Load Pickup)
• Generator Startup Timings
• Prime Movers Frequency Response Characteristics
• Generators Minimum and Maximum Limits
• Reactive Power Balance & Control of Voltages
• Shunt Capacitors and Reactors, Sizes and Locations
• Line and Cable Charging Currents
• Generator Reactive Capabilities (Leading and Lagging)
• Transformers Reactance and Staggering Tap Positions
• Customers’ Reactive Demand
• Protective Systems and Local Controllers
• Under-frequency Load shedding Relays
• Synchronizing Facilities and Synchro-check Relays
• Interlocking Schemes (Dead Bus Transfer)
• Relay Types Impeding Restoration (Inappropriate Operation/ Failure to Trip)
• Circuit Breakers with Deplete-able Stored Energy

 Sustained Overvoltage
 Switching Transient (Surges)
 Harmonic Resonance
 Overvoltage Limited Equipment
• Transformers: Exceeding Insulation Strength (BIL),Over Excitation,
• Harmonic Generation, Excessive Heating.
 Circuit Breakers
• Higher Transient Recovery Voltage (TRV), Re-Striking,
• Flash Over, Lower Interrupting Capability
 Surge Arresters
• Cause Operation and Prevent Reseal, Damage Arresters
Overvoltage of Concern

Protection & Control Issues During
Restoration
 Setting may be reviewed during restoration
 Over current relays
• Failure to operate due to low fault level during restoration
 Differential Relays Lacking Harmonic Restraints
• During Transformer Charging
 Out-of-Step Relays, Synchro-check Relays
• During Synchronization of Islands
 Negative Sequence Voltage Relays
• Untransposed line, Unbalanced load
 Volts per Hertz Relays
 Generator Under-Excitation Relays
 Low Frequency Isolation Scheme
 Over voltage Relays

Key Points on Over Voltage
 Ensure only fault free Lines has to be charged.
 Lower Voltage level lines should be given first priority.
 Charged from the end with higher fault level: Limit in Voltage Rise at Open End.
 If Buses have same fault level, then charge with bus with lower voltage.
 At the charging end, ensure that the voltage do not exceed 410kV :
 Bus reactors are to be taken into service.
 Charging end generators must operate at reduced voltage (less than 1 p.u) and
 in lagging p.f mode
 In case of high frequency, the same should be controlled first.
 Taking loads into service
 In case line reactor is available at only one end : Charge from end with out L/R to Limit in Voltage Rise
at Open End.
 At the synchronising end, control of standing phase angle (SPA) to less than 20 Degrees.
 Be Aware About Over voltage setting at Open End.
 Use Transformer as Bus Reactor during such condition.
 Generator to be kept at Manual Excitation Control and should be operated at reduced voltage to
ensure charging of long lines.

Keep Ready Reckoner to Meet the Over Voltage
Challenge
Check The Recovery Procedure : Train the Operator for these Calculation

Challenges experienced during 30th and 31st July
2012 Indian Grid Disturbance
• For black started power station, the required quantum of load commensurate
with generation build-up rate were not available.
• Tripping of self-started unit on 3rd harmonic, over-voltages, Under frequency
and mismatch in generation with remote loads over long EHV lines.
• Lack of preparedness for such emergency at Sub-station level.
• Delays encountered on account of commercial issues for obtaining the start- up
power supply from outside agencies.
• Generator LP-diaphragms bursting during the disturbance causing delay in their
start-up.
• Long start-up times taken by most Gas turbine generators.
• Lack of dedicated communication path.

Challenges in Restoration -2002 Grid Disturbance in
Western Region
I. Voltage Or Active Power Hunting
II. High Frequency Problem
III. Tripping of Auxiliary transformer at power
station on over-flux protection
IV. Faulty equipment at station caused delay
of start up power.
V. Load-Generation mismatch / excess load
addition causing tripping of Island:
VI. DG Set hunting
VII. In Many cases, high voltage problem
resulted in delay in extension of start up
power to thermal stations.
I. Gandhisagar, Bargi, Bango, Pench
II. Pench
III. Tons, Koyna-I,Birsinghpur,Jhanor
IV. Koyna-I, Birsinghpur ,Jhanor
V. Kawas
VI. Jhanor
VII. Koyna-I

Prevention of
Blackout

Source : CIGRE WG 34.08 Isolation and restoration policies against system collapse
Journey to the Blackout

Reasons for the Various Blackouts in the World
Source : CIGRE WG C2.21has conducted the analysis of the 18 major blackout
*Secondary causes are those that by themselves, would not have caused the disturbance to occur. However, they added to the severity of the disturbance, or complemented the
primary causes collectively that resulted in the disturbance.
**Exclude Indian Grid Disturbance on 30 and 31 July 2012
Main Cause Primary Secondary Total Contributions
Natural phenomena 8 0 8
Communication/Control System failure 4 1 5
Design and application errors 4 0 4
Operator errors 4 0 4
Primary equipment failure 3 0 3
Others (Insufficient Training) 2 1 3
Secondary equipment failure 1 1 2
Inadequate investment and complexity of system 2 0 2
Errors in maintenance 1 0 1
Excessive risks or inappropriate risk management 1 0 1
Security related (sabotage, etc.) 0 0 0
Total 30 3 33

Actions to minimise
frequency of interruption
Actions to minimise
initial extent of interruption
and its spread
Actions to
reduce duration
of interruption
Restoration
Containment
Prevention
• Defence plan
• Special protection scheme
• Restoration plan
• Online security management
• …
• Defence plan
• Special protection scheme
• …
• Planning policy
• Maintenance policy
• Power system analysis
• Telecommunications
• …
Measure
Mitigating Measures in Operations Horizon

Main Cause Measures to Prevent/Reduce
Likelihood of Occurrence
Measures to Minimizing/ Reduce Impacts of
Disturbance
Natural
Phenomena
None specifically identified
• Improve forecast (All Type of Forecast of IMD)
• Increase resilience of transmission equipment.
• Operate the power system in a more secure
mode than normal.
• Pro-active mobilization of staff (Keep ERS
Ready).
• Define and enforce minimum requirements for
connecting new generators to the grid (New
Element Integration).
• Better forest/bush fire containment methods

Main Cause Measures to Prevent/Reduce Likelihood
of Occurrence
Measures to Minimizing/ Reduce
Impacts of Disturbance
Communication/
Control System
failure
• Provide full redundancy of EMS, SCADA,
voice communication, etc.
• Provide full capability back-up control center
(Introduced in India)
• Perform more rigorous update of EMS
database and capability (State Estimator)
• Provide wide-area view and analysis
capability to operators (WAMS)
• Exchange of Frequent Data with other
operator
• Deploy resource to enhance observability
and controllability (Better Monitoring
System)
• Mobilise/dispatch staff to critical stations
• Setting up emergency control centre
and/or staffing backup control centre
Source : CIGRE WG C2.21 has conducted the analysis of the 18 major blackout

Main Cause Measures to Prevent/Reduce Likelihood of
Occurrence
Measures to Minimizing/ Reduce
Impacts of Disturbance
Design and
application
errors
• Implement a special maintenance plan for
vital substations (Critical Substation List)
• Regular tuning or revision to controller and
protection system tuning at key substations
and generating plants (Retuning of PSS/POD
and Mock Test of SPS)
• Periodic review of system protection
philosophy
None specifically identified

Measures to Minimizing/ Reduce Impacts
of Disturbance
Operator Errors
• Provide sufficient and frequent operator
training, with aid of simulators.
• Provide state-of-art information and
control system - SCADA/EMS and
emerging WAMS/WACS
• Develop on-line equipment diagnostic
systems and environment monitoring
information systems
• Effective use of normal security controls
(SCADA/EMS) and security analysis, including
overload relief measures
• Effective use of data from on-line equipment
diagnostic systems
• Effective use of data from on-line
environment monitoring information systems
• Effective use of SPS
• Help from other control center team
members
• Enhance Inter-TSO coordination to help
minimize operator errors

Measures to Minimizing/ Reduce Impacts
of Disturbance
Primary
Equipment
Failure
• New Investments (Check CT/PT)
• Strengthen maintenance program
• Strengthen connection requirements to
meet certain level of reliability
performance (SPS even for N-1)
• Develop measurement systems electric
and energy signals and values which
would otherwise have been available to
enable a better monitoring of processes
and of equipment
• Installing Special Protection System as a
“Safety Net” to contain potential cascading.
• Carry adequate replacement equipment
inventory to minimize down time.

Some Statistic : Be Vigilant About Reality

Primary Reason for Grid Event in Western Region

Grid Restoration Challneges and Strategy

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