WORKSHOP ON BLACK START RESTORATION PROCEDURE IN SR

WORKSHOP ON BLACK START RESTORATION PROCEDURE IN SR SRLDC BANGALORE 20 th March 2012

This Presentation Covers … … … üDefinitions üEmphasis of Black Start Restoration in IEGC üCauses of Blackouts üRestoration Approach üSignificance to present Scenario üSteps to Prevent Blackouts üDo’s and Don’t during Black start Restoration üOpen Discussion 2

Grid Incident Tripping of one or more power system elements which requires re-scheduling of generation or load, without total loss of supply at a sub-station or loss of integrity of the grid at 220 KV and above. Category GI-1 without total loss of supply at 'a sub-station or loss of integrity of the grid at 220 KV. Category GI-2 without total loss of supply at a sub-station or loss of integrity of the grid at 400 KV and above.

GRID DISTURBANCE "Grid Disturbance" is tripping of one or more power system elements of the grid 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. The power system in different regions is being interconnected and very often an incident initiated in one region can lead to a disturbance in other region also.

Categorization of Grid Disturbance (GD) Category GD-1 When less than 10% of the, antecedent generation or load in a regional grid is lost. Category GD-2 When 10% to less than 20% of the antecedent generation or load in a regional grid is lost. Category GD-3 When 20% to less than 30% of the antecedent generation or load in a regional grid is lost. Category GD-4 When 30% to less than 40% of the antecedent generation or load in a regional grid is lost. Category GD-5 When 40% or more of the antecedent generation or load in a regional grid is lost.

BLACKOUT A blackout refers to the total loss of power to an area and is the most severe form of power outage that can occur. Blackouts which result from or result in power stations tripping are particularly difficult to recover from quickly. Outages may last from a few minutes to a few weeks depending on the nature of the blackout and the configuration of the electrical network

Black Start Restoration Objective To achieve restoration and re-synchronisation of constituent systems effected, in case of a grid disturbance, in the shortest possible time, taking into consideration all essential requirements like traction loads, core sector industrial loads, generation capabilities and the operational constraints of Regional Transmission System.

Emphasis of Black Start Restoration in IEGC 5. 2 (n) System Security Aspects: Procedures shall be developed to recover from partial/total collapse of the grid and periodically updated in accordance with the requirements given under section 5. 8. These procedures shall be followed by all the Regional constituents to ensure consistent, reliable and quick restoration. 5. 8 Recovery Procedures: (a) Detailed plans and procedures for restoration of the regional grid under partial/total blackout shall be developed by RLDC in consultation with all Regional constituents / RPC Secretariat and shall be reviewed/updated annually.

Emphasis of Black Start Restoration in IEGC (5. 8. b) Detailed plans and procedures for restoration after partial/total blackout of each Constituents system within a Region, will be finalised by the concerned constituents in coordination with the RLDC. The procedure will be reviewed, confirmed and/or revised once every subsequent year. Mock trial runs of the procedure for different sub-systems shall be carried out by the constituents at least once every six months under intimation to the RLDC. (5. 8. c) List of generating stations with black start facility, inter-State/inter regional ties, synchronising points and essential loads to be restored on priority, should be prepared and be available with RLDCs.

Emphasis of Black Start Restoration in IEGC (5. 8. d) The RLDC is authorised during the restoration process following a black out, to operate with reduced security standards for voltage and frequency as necessary in order to achieve the fastest possible recovery of the grid. (5. 8. e) All communication channels required for restoration process shall be used for operational communication only, till grid normalcy is restored.

Probable Causes of Blackout & Possible System Problems • Persistent Fault Condition • Malfunctioning of Protection System • Violation of Grid Discipline • Un planned Outages • Inadequate Training & • Manual Error UNIT FAILURE TRANSFORMER/ LINE FAILURE REDUCED NETWORK REDUNDANCY OF GENERATION LOSS BUS ISOLATED LINE OVERLOAD OR UNSATISFACTORY BUS VOLTAGE INSUFFICIENT GENERATION LOSS OF LOAD SYSTEM COLLAPSE ISLANDING

Modes of Operation of Grid NORMAL RESTORATIVE A L E R T EMERGENCY

Restoration Objectives • Restoring normal system operation as quickly as possible • Synchronising of at least one unit at all power station • Restoring Essential Loads • Establishing All Interconnections • Starting Economic Dispatch • Starting Allocation of ISGS Share • Minimising Amount of Un-served Energy

Restoration Problems • Impaired Communications, Limited Information • Re-assembling Tie Elements of Power System • Unfamiliarity with the situation (Does Not occur Regularly) • Time Constraints • Information to be furnished to Authorities – Pressure on Operators

Restoration Tasks Various Steps to be followed in Black Start Restoration are • SYSTEM STATUS DETERMINATION • PLANT PREPARATION SERVICES/START-UP • NETWORK PREPARATION • NETWORK ENERGISATION • LOAD RESTORATION • SYSTEM REBUILDING

System Status Determination • Extent of Blackout and Actual Requirement • Identification of Boundaries of Energised Areas • Ascertaining Frequency & Voltage of Energised Areas • Status of Generating Plants ( Hot / Cold / House Load ) • Non-availability of Elements (LC / Fault etc. , ) • Overloading of Elements • Loads Interrupted by Under Frequency Relays • Operation of Direct Tripping • Status of Breakers

Plant Survival and Start-up Power Requirement Survival Power Supply to the Plants at the earliest with available arrangement (DG sets) for • Turbine emergency oil pump • Jacking oil pumps • Barring gear of the turbine • Lubricating oil pumps • Emergency lighting • Battery charger • Compressor for CB The survival power requirement of 120 MW unit is of the order of 250 - 350 KW while the requirement of 210 MW unit is of the order of 350 - 500 KW and for 500 MW unit, it is in the order of 1250 - 1500 KW. As a general rule, the survival power requirement would be around 0. 25 - 0. 30% of the unit capacity.

Plant Start-up Power Requirement • The start up power is the power required for the auxiliaries while the generating unit is restored. The requirement of start up power by various units is as follows : Nuclear & Thermal: 7 to 8% of the unit capacity Hydro: Gas: • 0. 5 to 1% of the unit capacity 1. 5 to 2%of the unit capacity The start up power requirement for starting thermal units is considerably high as the major auxiliaries like BFP, ID Fan. FD fan, CW pumps etc. are of bigger size and the starting torque is considerable. In case of hydro units, the requirement of start-up power is not significant as there are very few auxiliaries.

Network Preparation • 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 • Automatically Switched Capacitors and Under Frequency Relays may have to be kept out of service at the initial stage

Network Energisation - Considerations • Identify the Important and Essential Loads to be Restored First • At Every Stage it Should Satisfy – Reactive Power Balance – Load Generation Balance – Protection and Plant Control System Requirements • HVDC Import – Only when Minimum Fault Level is available • Paralleling of Islands through Strong Links

Network Energisation – Load Generation Balance • Type of the Load – Peak or Off-Peak – Cold Load Inrush • Generator Capacity • Minimum Loading capability of Generator • Response to Sudden Load Pick-up • Time Elapsed (Hot Start)

Network Energisation – Plant Control System Considerations ELECTRICAL CONSIDERATIONS • Voltage Regulator to be switched to Automatic Control (From Manual) only when the unit reaches a Minimum Operating Point and a sufficient VAR generation is established • Protective Relays such as Volts per Hz, Out of Step, Under Excitation, Distance, Frequency & Field forcing can initiate an undesirable Response or Generator Trip during start-up

Network Energisation – Load Restoration During Restoration Effect of Each Restoration Action on following to be Considered • Generator Loading • Transmission Line Loading • Load Angle • Rate of Loading • Response of the Generator to Load Change • Change in System Frequency and Operation of Under Frequency Relays • Fluctuating Loads – Example: Traction, Furnace, etc. ,

Restoration Strategies BUILD DOWN OR SEQUENTIAL STRATEGY BUILD UP OR PARALLEL STRATEGY

Build Down or Sequential Strategy • Re-energisation of Bulk Power Network • Balanced Step-by-Step Restoration of Loads and Generation Suitable for • Small Systems Not having Long EHV Lines or • Predominantly Hydro System with High Reactive absorption Capability or • For Large Systems with very Compact Service Territories Usually selected when strong neighbouring Inter. Connection Assistance available Inter-connection status is to be Assed, Hence time consuming & Tasking.

Build Up or Parallel Strategy • Simultaneous Restoration of Islands / Sub-Systems followed by their Mutual Synchronisation • Usually selected in case of a Complete System Collapse and lack of inter-connection assistance • Relatively Quick Process • Requires Several Operating Teams and Adequate Communication Facilities For Mutual Co-ordination

Special Considerations • Firm Transmission in the Inter-connection between the Sub-Systems and firm Generation Capacity in each Sub -System to be ensured during early stages on Restoration • Deactivation of Automatic Load Shedding and Automatic Switched Capacitors during initial stages • Restoration of Smaller Radial Loads followed by Low Voltage A/C network loads while Maintaining Reasonably Constant Real to Reactive Power Ratio • Picking-up Small Blocks of Loads followed by as Large as possible, without risking dangerous decline of Frequency, as Restoration proceeds • Keeping Generator Terminal Voltages relatively Low initially, and Adjusting Transformer Taps, subsequently as Restoration proceeds

Restoration Planning – General Guidelines Restoration Team • A Commando Group with Participation of Experienced / Knowledgeable personnel from respective fields like Protection, Communication, Operation, System Analysis etc. , shall rush in to the control room to assist early restoration. • Review of System Characteristics (Relevant to Restoration)

Restoration Planning – Common Concerns • Time Consuming nature of Switching Operations • Frequency Response of Prime Movers to Sudden Load Pick-up • Cold Load inrush, Power Factors and Coincident Demand Factors • Availability of Governor Facilities of Units

Logistics & Communication • Close and Continual Co-ordination among Power System, Power Plan and Field Operators • Neighbouring utilities, Authorities to be informed time to time about the Progress of Restoration. • To depend more on the utilities’ own communication facilities • Fall-back arrangement in case of Communication Failure

Audit & Updates • A Technical person outside the Restoration Team should Audit the Activities • Audited Restoration Plan must be updated • Documents must be revised Regularly to reflect the latest characteristics of the system • Changes in the SCADA / EMS installation or major plant control, Available tools also to be incorporated

Training • Instruction Manuals or Audio-Visual tapes, for independent study • Class Room Instructions • Learning from past experience during Restoration • Operator Training Simulator • Role Play • Operator’s Problem Solving capability can also be explored and developed • Alternative source of finding New Ideas • Detailed interaction with the persons involved in Restoration

Documentation Purpose: Training, Reference, Improvement of Restoration Procedures • Should be Readily Accessible and Easily Understood • Should be stored in a Convenient Media for Quick Processing • Should be illustrated with Familiar Diagrams and Charts • Actions rejected and incorporated in the plan must be Recorded

Power System Restoration Cycle Actual Restoration Event Restoration Drills Restoration Training Assess Lessons Learned Revise Restoration Plan And Procedures Engineering Analysis and Studies

Significant to Present Scenario • Complacence on no major grid disturbance for many years • Consistent increase in Demand – Supply Gap • Many Sub-stations are very old and warrants replacement of equipments and thorough checking of cabling etc. , • Delay in execution of New Projects • Trunk Lines are loaded beyond its Normal rated Capacity • Planning Criteria for n-1 condition only

Steps to Prevent Blackouts • Islanding Schemes for all Major Generating Stations • Ring Main System for all Major Load Centers • Special Protection Schemes for critical Flow Gates • Planning Transmission System for n-2 Criteria • Effective VAR Management • Proper Planned maintenance of Equipments & Protection Schemes • Automatic Demand side Management Prevention is Better than Cure

Do’s and Don’ts during Black Start Restoration • Readily have the Single Line Diagrams of the Station • • • Readily have the Black Start Restoration Scheme Diagrams • Readily have the outage details • Communicate the Concerned Station in-charge and Load Despatch Centre immediately • • Assign the Responsibilities to the available staff clearly • Follow the instruction of Load Despatch Centre in full • Send the preliminary report / observation to LD Do not Panic Do not keep all the communication channels busy simultaneously Do not entertain external enquiries till the restoration complete Direct the enquiries to the designated nodal officer in HQ PR Do not indulge in argument during restoration

Thank You