Grid Restoration Procedure - Central Electrical Authority

Report
Workshop on Crisis & Disaster
Management of Power Sector.
17-04-2013
RESTORATION PROCEDURE
N.Nallarasan, DGM
NLDC New Delhi
17-04-2013
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
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
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.
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
OF
GENERATION
LOSS
BUS
ISOLATED
INSUFFICIENT
GENERATION
LOSS OF
LOAD
SYSTEM
COLLAPSE
REDUCED
NETWORK
REDUNDANCY
LINE OVERLOAD
OR
UNSATISFACTORY
BUS VOLTAGE
ISLANDING
Modes of Operation of Grid
NORMAL
RESTORATIVE
In Extremis
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:
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.
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 Aessed, 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
Experienced
/
Group
with
Knowledgeable
Participation
personnel
of
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,
incorporated
Available
tools
also
to
be
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
• 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
preparedness Aspects(1)
• 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(2)
• NLDC also prepares the restoration procedure for interregional 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(3)
• 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 .
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

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