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TRANSCRIPT
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
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
Contents
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
Dynamic Security Assessment
Thermal, Voltage and Transfer Security
Assessment Tool:
VSAT
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.)
VSAT Overview
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
Scenarios
“Stability Limit” is the pre-contingency transfer
level corresponding to the first post-contingency
nose point (Pcm).
Stability Limit
“Security Limit” is the pre-contingency transfer level
corresponding to the first pre/post-contingency
security criteria (margin, voltage, etc.) violation.
Security Limit
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)
Security Criteria
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.
Analysis of Scenario
VSAT uses a special PV-based method to select a desired number of severe contingencies from a specified list. • The method accounts for all non-
linearities (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
Contingency Screening
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
Propose corrective
actions
Analyse simulation
result
Conduct simulation
Collate & verify input
data
Highlight violation in
report
DSSA Process Flow
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
Spinning Reserve
Load Profile
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 in-house 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
East
North
South
Central
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
Loss of 1 unit Bakun
Rotor Angle
Bus Voltages
TSAT Example
DSATools Output Analys is 10.0
Powertech Labs Inc.
Copyright © 2012 All rights reserved
Friday, March 02, 2012, 10:41:24
Buf. Binary Result File Scenario Contingency
Bus # Bus Name ID Buf.Bus f requency (Hz)
Time (sec)
0.00 6.00 12.00 18.00 24.00 30.00 48.60
48.88
49.16
49.44
49.72
50.00
2 seb2012.bin Base Scenario 1 -- 3P FAULT AT BAKUN PS TRIP BAKUN 1 UNIT1
85422 BETG275 275. 2
85450 BINT275 275. 2
85470 BKPS275 275. 2
85421 ENKI275 275. 2
85451 KEMA275 275. 2
85412 KSAM275 275. 2
85410 MATA275 275. 2
Prony Analysis
Frequency Behaviour during 1 unit Bakun trip
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.
Conclusions
TUTORIAL SESSION ANY QUESTIONS?
Thank You
Operation Studies
Operation Planning Unit
System Operation Dept
Transmission Div