Workshop on Crisis & Disaster Management of Power Sector

RESTORATION PROCEDURE N.Nallarasan, DGM NLDC New Delhi

This Presentation Covers … … … Definitions Emphasis of Black Start Restoration in IEGC Causes of Blackouts Restoration Approach Significance to present Scenario Steps to Prevent Blackouts Do’s and Don’t during Black start Restoration Open Discussion 3

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 Incident

"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. GRID DISTURBANCE

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 When20% 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. Categorization of Grid Disturbance (GD)

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

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. Black Start Restoration Objective

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.List of generating stations with black start facilityinter-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.

UNIT FAILURE INSUFFICIENT GENERATION TRANSFORMER/ LINE FAILURE LOSS OF LOAD REDUCED NETWORK REDUNDANCY LINE OVERLOAD OR UNSATISFACTORY BUS VOLTAGE BUS ISOLATED LOSS OF GENERATION ISLANDING SYSTEM COLLAPSE 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

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

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 Objectives

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 Problems

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 Restoration Tasks

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 System Status Determination

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 Plant Survival and Start-up Power Requirement The survival power requirement of 120 MW unit is of the order of KW while the requirement of 210 MW unit is of the order of KW and for 500 MW unit, it is in the order of KW. As a general rule, the survival power requirement would be around % 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: 0.5 to 1% of the unit capacity Gas: 1.5 to 2%of the unit capacity The start up power requirement for starting the 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.

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 Preparation

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)

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 – Plant Control System Considerations

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.,

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

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 Aessed, Hence time consuming & Tasking. Build Down or Sequential 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 Build Up or Parallel Strategy

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 Special Considerations

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 – General Guidelines

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 Restoration Planning – Common Concerns

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 Logistics & Communication

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 Audit & Updates

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 Training

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 Documentation

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

Significant to Present Scenario 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

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-1-1 Criteria Effective VAR Management Proper Planned maintenance of Equipments & Protection Schemes Automatic Demand side Management Prevention is Better than Cure

Region wise restoration procedure is being updated as per IEGC by RLDC’s in consultation with states. –Sub systems are formed by carrying out system studies considering black start facilities for extending the start up supply to thermal /nuclear generating units. Alternate path’s of restoration are also studied and incorporated Extending power supply to Essential loads and traction also included in the restoration procedure preparedness Aspects(1)

NLDC also prepares the restoration procedure for inter- regional basis. Mock drill exercise of black start facilities is being carried out twice in a year and has been monitored at RPC level. Mock Drill Exercise up to the load point has been suggested DG sets and Batteries health being checked Healthiness of protection systems being monitored. Workshop on Black start restoration procedure has been organized by RLDC once/twice in a year. Documentation in Hard and soft copy available in the control room. preparedness Aspects(2)

Details of Nodal officers from LD’s,generating /substations are being regularly updated and monitored at RPC level Emergency phone numbers list has been available in the control room Mock drills on Fire fighting has been carried out. preparedness Aspects(3)

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