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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