Use of Dynamic Security Assessment
for Blackout Prevention in TNB
AORC-MNC CIGRE Technical Meeting
Sunway Hotel @ Sunway Lagoon
2 – 4 May 2012
Aznan Ezraie Ariffin & Tajul Ariffin Sulaiman
Contents
1. Introduction to TNB’s Dynamic Security
Assessment
2. Voltage, Thermal and Transfer
Assessment
3. TNB’s Daily System Security Assessment
(DSSA)
4. Transient and Oscillatory Stability
Assessment
5. Conclusions
Dynamic Security Assessment
 To comply with statutory and license
requirements, Malaysian Grid Code and
Transmission System Reliability Standards, TNB
embarks on a systematic Dynamic Security
Assessment (DSA) process
 This off-line process is performed on a multi time
scale ie daily, monthly, and annually looking
forward into the next 2 years
 This is in addition to the on-line security
assessment conducted by the real-time
operators employing the applications of the EMS
Thermal, Voltage and Transfer Security
Assessment Tool:
VSAT
VSAT Overview
 Comprehensive tool for voltage (and thermal)
security assessment of power systems.
 Uses static analysis for the main security
assessment and transfer limit computations.
 Contingency Screening module classifies
contingencies based on their stability margin.
 Remedial Action Module finds the most effective
Preventive/Corrective control actions based on
user specified priorities.
VSAT Overview
 VSAT greatly facilitates the voltage stability analysis of
large number of system conditions, contingencies and
power transfers.
 Provides detailed information regarding:
• Critical contingencies and voltage/thermal security violations
• Proximity (margin) and mechanism of voltage instability
 In the on-line application, determines the security of:
• Current system state (as obtained from the EMS state
estimator)
• Forecasted future states (hour-ahead, day-ahead, etc.)
Scenarios
 The user may setup any number of scenarios to
be analyzed, each defined by:
•
•
•
•
•
•
Base case condition (powerflow data)
Transfer definition
Contingencies
Security Criteria
Analysis and solution control options
Other required data
 All data (except base case powerflow) are
optional.
• Depend on selected analysis options
Stability Limit
 “Stability Limit” is the pre-contingency transfer
level corresponding to the first post-contingency
nose point (Pcm).
Security Limit
 “Security Limit” is the pre-contingency transfer level
corresponding to the first pre/post-contingency
security criteria (margin, voltage, etc.) violation.
Security Criteria
 Any combination of:
• Voltage stability (always implied)
• Voltage stability margin (P, Q, mixed
combination)
• Voltage limits (low/high and
decline/rise)
• Reactive reserve limits (per source or
group of sources)
• Thermal limits (as percentage of line
and transformer ratings)
Analysis of Scenario
 VSAT determines if the base case
meets the specified security criteria
under all contingencies.
 When transfer analysis is requested,
VSAT determines how far the
transfer can be increased before a
contingency causes violation of
security criteria.
 In either case, a variety of reports
are produced to show security
violations, voltages, flows and other
system information, PV curves, etc.
Contingency Screening
 VSAT uses a special PV-based
method to select a desired number
of severe contingencies from a
specified list.
• The method accounts for all nonlinearities (does not use inaccurate
linearized indices or interpolated
trajectories)
• Accurately classifies the
contingencies based on their true
voltage stability margin for the
specified power transfer for each
scenario
Daily System Security Assessment
VSAT application in TNB
Daily System Security Assessment (DSSA)
 Process of evaluating the system security on a
day-ahead basis
 The objective is to ensure the system is always
secure and reliable during operation, meeting
the Malaysian Grid Code Requirement, TSRS
and Energy Commission License
 System Security implies that the grid system will
continue to operate within the acceptable limits
described earlier following outages or tripping of
one or more components of the grid system
DAILY STUDY (Daily System Security
Assessment DSSA)
 Contingency analysis performed are:
• Loss of one 132kV, 275kV or 500kV transmission
line/underground cable
• Loss of one 500/275kV (XGT) or 275/132kV (SGT) grid
transformer
• Loss of one generator unit
• (n-2) contingency for adjacent 275 & 500kV system
• Selected 275 kV bus bar contingency (occasional)
• Other credible contingencies e.g. total loss a generating
station, single busbar and ROW
DAILY STUDY (Daily System Security
Assessment DSSA)
What determines a secure operation?
System is secure when all parameters fall within
the Criteria adopted
1. Voltage (0.9 to 1.1 pu)
2. Loading on lines and transformers (<100%
of equipment rating)
3. No load loss observed under (n-1)
contingency
DSSA Process Flow
Collate & verify input
data
Conduct simulation
Analyse simulation
result
Highlight violation in
report
Propose corrective
actions
INPUTS INTO DSSA
Data
Description
Network data
Controlled data file of power flow in PSS/E ™
format.
Network off-point
List of network off-point
Generation schedule
Half-hourly generation schedule of every
generator
Outage schedule
List of daily outages
Load demand
Daily load profile at day & night peak
Diagrams (e.g grid drawing,
substation SLD)
System & substation network topology
DSSA Input Data
Transmission Outage
Generation Profile
Load Profile
Spinning Reserve
Simulation
 After input data has been verified,
snapshot of the system at the highest
forecasted demand level for the next day
is simulated
 Simulation is performed via a power
system simulation software to generate
power flow in the network
CONTINGENCY ANALYSIS (n-1), (n-2)
 Contingency results are analyzed to check for
violation on the pre-defined security criteria
 When violations occur, corrective actions will be
proposed to mitigate the problems
 Corrective actions are recommended in the
methods given below:
• Changes of off-points
• Generator re-dispatch
Corrective Measure Library
 For most of n-1 & n-2 contingency violations,
proposed corrective measures are
automatically flagged-out
 The list of the corrective measures is invoked
thru analysis of the contingency runs via inhouse developed MS-Excel Macro file
 The auto-corrective measure saves time for
engineers to come out with a solution of a
particular contingency
Transfer Analysis- Example
North
East
Central
South
Real Time Contingency Analysis
EXAMPLE OF AUTO GENERATED RESULTS
EMS Overview of TNB System
Dynamic Security Assessment
Transient Security Assessment Tool
TSAT
Overview of Transient Security
Assessment
 Transient Security Assessment (TSA) of
power systems determines:
• How well a particular system condition can
withstand credible contingencies (“degree of
stability”)
• What is the maximum secure power transfer
under these contingencies (“stability limit”)
• What can be done to prevent the instability if
the system will be unstable for a critical
contingency (“remedial action schemes”)
Overview of Transient Security
Assessment
 TSA covers all forms of system dynamic
performance during the transient period
following a contingency, including:
•
•
•
•
Synchronism of the system (“transient stability”)
Low frequency oscillations (“small-signal stability”)
Transient voltage violations (“fast voltage stability”)
Transient frequency violations (“frequency
stability”)
Application Scope of TSAT
 TSAT has been developed to provide solutions
for the following problems:
• Transient security assessment (TSA) including stability
limit determination
• Dynamic voltage stability analysis (with necessary
models for simulations up to a few minutes)
• Frequency stability analysis
 TSAT can be used for on-line TSA or for off-line
studies, with the exact same analysis
capabilities.
Transient Stability
 Transient Stability (TS) refers the ability of a power
system to maintain synchronism when subjected to a
severe disturbance, such as:
•
•
•
•
Fault on a transmission element
Loss of transmission elements
Loss of generation
Loss of loads
 In transient stability problem, the main concern is the
electro-mechanical transient performance of the
system in the frequency range of roughly 0.1 to 5.0 Hz.
• Note that this is different from the electro-magnetic transient
problem (“EMTP”) and the slow voltage collapse dynamic
problem
Characteristics
 Responses involve large excursions of system
quantities; thus nonlinearity plays an important role
 Stability depends on the initial operating condition
(“powerflow”) of the system, the dynamic device
characteristics (“dynamics”), and the severity of the
disturbance (“contingency”)
 The study period is usually in the range of 5 to 10
seconds (longer time frame may be considered for
oscillatory problems)
 The most practical and accurate solution method
(“traditional approach”) is the time-domain simulation
TSA Problems
 TSA extends from the conventional transient
stability analysis to include:
• Contingency screening (critical mostly for on-line
applications)
• All forms of dynamic characteristics, not only transient
stability
• System security with quantitative measurement, i.e., not
only to identify instability conditions, but also to give
degree of stability (“proximity to stability”)
• Determination of stability limits
• Identification and design of appropriate remedial
measures to improve transient security
Stability Limit Problem
 Transient security often constitutes a constraint in
determining the maximum power transfer in a system.
• The objective is to find the maximum power transfer between
two regions of the system, subject to required transient security
criteria
• The power transfer may be the total output of a plant, or
exchange between two control areas, or anything defined by a
power transaction
• The details of the power transfer are described by the power
transaction (source, sink, amount to be transferred)
• This maximum power transfer, together with the thermal limit and
voltage stability limit, determines the Total Transmission
Capacity (TTC)
TSAT Applications
 Transient stability analysis in planning and operation
studies
 On-line transient security assessment
 IPP integration studies
 Control design and tuning (with SSAT)
 Small signal stability studies (with SSAT)
 Voltage stability studies (with VSAT)
 Design of special protection systems (SPS)
 Verification of device model and performance
(generator controls, FACTS, SPS, etc.)
 Black-start analysis
 Construction of system responses in post-mortem
analysis of system incidents
 Other
Monthly System Security Assessment
TSAT application in TNB
TSAT Example
Rotor Angle
Loss of 1 unit Bakun
Bus Voltages
TSAT Example
Friday , Marc h 02, 2012, 10:41:24
Buf.
Binary Result File
Scenario
Contingency
2
seb2012.bin
Base Scenario
1 -- 3P FAULT AT BAKUN PS TRIP BAKUN 1 UNIT1
Bus f requency (Hz)
50.00
49.72
Bus #
Bus Name
85422
85450
85470
85421
85451
85412
85410
BETG275
BINT275
BKPS275
ENKI275
KEMA275
KSAM275
MATA275
ID
275.
275.
275.
275.
275.
275.
275.
Buf.
2
2
2
2
2
2
2
49.44
Prony Analysis
49.16
48.88
48.60
0.00
6.00
12.00
18.00
24.00
30.00
Time (sec)
DSATools Output Analy s is 10.0
Frequency Behaviour during 1 unit Bakun trip
Powertec h Labs Inc .
Copy right © 2012 All rights res erv ed
Conclusions
 TNB’s current DSA has been effective in
preventing national blackout
 In fact, it has enabled TNB high voltage network
to be operated with a comfortable margin thus
enable economical operation
 This has avoided the need to go into restoration
process, which is already in place
 Nevertheless, vigilance is needed as the system
is growing bigger and difficulty in building
additional infrasctructures.
TUTORIAL
SESSION
ANY
QUESTIONS?
Thank You
Operation Studies
Operation Planning Unit
System Operation Dept
Transmission Div