system reliability
DESCRIPTION
system reliabilityTRANSCRIPT
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EE5712 Power System Reliability:: Introduction
Panida Jirutitijaroen
1EE5712 Power System Reliability 12/27/2010
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About Me
Panida Jirutitijaroen.
Bangkok, Thailand.
Research Area:
Reliability Theory Applied to Power Systems.
Optimization Techniques Applied to Power Systems.
http://www.ece.nus.edu.sg/stfpage/elejp/
Email: [email protected]
Office: E2-03-19
12/27/2010 EE5712 Power System Reliability 2
http://www.ece.nus.edu.sg/stfpage/elejp/mailto:[email protected]
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Outline
About this class
Introduction to reliability
Basic steps in system reliability analysis
Introduction to power system reliability
Power system reliability indexes and criterion
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ABOUT THIS CLASS
Overview
Assessment
Scope
Objective
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Overview
Lecture: Friday 6-9 PM @ E4-04-05. From August 27th onwards, well meet at PC cluster 3
@ E2-03-06.
15-min break 7-7:15 PM.
Consultation hours on Tuesdays 5:30-6:30 PM. 3 time slot, 20 mins each.
Make appointment using IVLE.
Homework will be posted before class on IVLE.
Lecture notes will be posted after class on IVLE.
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Assessment
Three exams. Exam1 20%: 25/09 (Saturday)
Exam2 20%: 06/11 (Saturday)
Final 40%: 01/12
Homework 20%, your own original work. Plagiarism will be taken very seriously.
Homework to be submitted before class starts. Homework submitted after the class starts will not be graded.
See tentative syllabus.
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Expectation
Attend lecture.
Do homework.
And,..
Please be considerate to other classmates and lecturer by coming to the class on time. Lecture will start at 6PM.
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Scope
Power System Reliability
Electric power
System
Reliability
Reliability theory applied to power systems
Analytical and simulation tools to conduct reliability analysis
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Road Map
Introduction to power system reliability (1 lec)
Probability theory and Reliability theory (2 lec)
Stochastic process (1 lec)
Analytical methods for reliability analysis (1 lec)
Frequency balance technique (1 lec)
Simulation methods (1 lec)
Single-area reliability analysis (2 lec)
Composite system and multi-area reliability (2 lec)
Distribution system reliability analysis (1 lec)
Theory
Application
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Objectives
What you will learn from this class
1. Understand basic reliability concepts and reliability measures
2. Be able to perform reliability analysis of a small system using analytical tools.
3. Be able to perform reliability analysis of a large system using simulation tools.
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INTRODUCTION TO RELIABILITY
What is reliability?
What causes a system to fail?
How to model uncertainties?
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Example 1: You Are The Weakest Link!?!?
"A chain is only as strong as its weakest link
Does this mean that system reliability is determined by the least reliable component in the system?
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Example 2: Identical Transmission Lines
Which system is more reliable?
Which system is likely to fail more than another ?
Next question is how much?
Line 1
Line 2
G Load
System A
Line 1
G Load
System B
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Example 3: Non-Identical Transmission Lines
Which system is more reliable?
Depend on t-line capability to deliver load, generation capacity, load level, how each line perform
How to quantify line performance?
Line 1
Line 2
G Load
System A
Line 1
G Load
System B
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Example 4: Identical Generators
Which system is more reliable?
Which system is more cost-effective?
100 100 100
System A
Load 100 MW
100 100
System B
Load 100 MW
100
System C
Load 100 MW
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Example 5: Non-Identical Generators
Which system is more reliable?
Depend on how each generator perform
How to quantify generator performance?
100 100 100
System A
Load 150 MW
150 150
System B
Load 150 MW
300
System C
Load 150 MW
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What Is Reliability?
Ability of a component/system to perform its intended function
Within a specified period of time
Under stated condition
Qualitative sense in terms of performance function, time, and surrounding conditions
How to quantify reliability?
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Reliability
Relate to the absence of failures, that due to random phenomenon
Define numerically as average or mean value
Can be treated as a parameter
Can be traded off with other parameters such as cost
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What causes a system to fail?
Human factors
System design
Operation condition
Maintenance procedure
Deterioration (function of time)
Random failures
Uncertainties
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How to model Uncertainty?
Probability of failure Chance that a component will fail
Probabilistic value with no unit
May be difficult to interpret
Frequency of failure In terms of number of failure within specified time
Easier to predict from history
Express in per hour, per day, per year
We will discover later on in this course how to relate frequency of failure to probability of failure
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Example 5: Transmission lines
Given that each system has the following level of reliability
Which system is more reliable? Which system is more cost-effective?
100 MW
100 MW
G Load100 MW
System A
100 MW
G Load 100 MW
System B
System Failure Probability Cost (million SGD)
A 0.009 70
B 0.01 25
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Example 5: Identical Generators
If each system has the following level of reliability and cost
Which system is more reliable?
Which system is more cost-effective?
100 100 100
System A
Load 100 MW
100 100
System B
Load 100 MW
100
System C
Load 100 MW
System Failure Probability
Cost (million SGD)
A 0.001 300
B 0.01 200
C 0.1 100
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Motivations for Quantitative Reliability
To evaluate system performance
System design purpose
Trade-off reliability with cost
Increasing complexity of systems
Competitiveness
Establish standard in operation procedure
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BASIC STEPS IN SYSTEM RELIABILITY ANALYSIS
Objective of the analysis
Component modeling
System modeling
Performance function
Reliability Evaluation
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Objective
Interest to know the likelihood that a component or a system will fail.
Time-to-failure distribution of a component/system.
Helps to predict the failure probability at any point in time
For a complex system, need to estimate reliability index for design and operation purposes.
Need to start with the component modeling
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Component Modeling
Identify components in the system
Describe state of each component
For example, a generator has two states, up or down.
In terms of probability distribution
For example, a generator fails with probability of failure = 0.01.
Stochastic process model
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Observation of A Component
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Time
Z(t)
0
1
2
Time
Z(t)
0
1
2
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System Modeling
System configuration/topology
How each component interact
C1 C2
C1
C2
C1 C2 C8
C6 C3 C9
C5 C11 C7
C10 C4 C12
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Need to know how each device causes a system to fail!
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Performance Function
To evaluate system reliability
Recall,
Need to define intended function
Ability of a system to perform its intended function
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Reliability Evaluation
Each component described by random variables
For example, a generator has 3 capacity output, 100 MW with 0.85 probability, 50 MW with 0.14 probability, 0 MW with 0.01 probability
System states constructed from possible combinations of component states
Evaluate performance function of each system state
Calculate reliability index
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INTRODUCTION TO POWER SYSTEMS
Functional Zones in Power Systems
Objective of Reliability Analysis
Levels of Reliability Analysis
Power System Reliability Indexes
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Functional Zones of Power Systems
Generation system
Generators
Load
Transmission system
High voltage transmission lines
Distribution system
Low voltage transmission lines
End users
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Main Components of a Power System
Generation (11 36 KV)
Transmission and distribution (110 765 KV)
Load (0.12 138 KV)
Industrial customer (23 138 KV)
Commercial customer (4.16 34.5 KV)
Residential customer (120 240 V)
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Generation Capacity in Singapore
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Transmission and Distribution
Interconnected network Transformers used to step up voltages from generation
units to transmission-line. High voltage used when transmitting power to lower I2R
loss for better efficiency. Distribution systems can provide power at different voltage
levels for different loads.
Transmission network Distribution network
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North American Electric Power Connections
http://www.nerc.com/regional/NERC_Interconnections_color.jpg
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Singapore Power Grid
Zone Maximum Import capacity (MW)
A 1275
B 1275
C 1275
D 1275
400 kV, 230 kV, and 66 kV
Full underground cable
Four 230 kV zones connected by meshed 400 kV
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Load
Varies with time
Moment-to-moment fluctuations
Hour-to-hour changes
Daily
Weekly
Seasonal
Base load counts for less than a half of peak load.
Typical weekly load curve, data from ERCOT
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Sun. Mon. Tue. Wed.0
1
2
3
4
5
6
x 104
Day
Load (
MW
)
ERCOT Weekly Load Curve from Aug. 19th to Aug. 22, 2006
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Singapore Electric Demand
Peak demand in 2007 is 5946 MW. Electricity demand in 2007 is 41134 GWh. 39
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Operational Conditions
Economic operationCost of operation differs by type of fuel.How to operate the system with least cost?
Secure operationComponent physical limit. How to operate the system securely?
Reliable operationPower Quality, interruptions, brownout and blackoutHow to operate the system reliably?
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Uncertainties in Power Systems
Generation
Generating units with failure and repair rates
Generating capacity associated with probability
Transmission line capacity
Transmission line with failure and repair rates
Transmission line capacity associated with probability
System load
Vary with time
Construct load distribution from history
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Objective of Reliability Analysis
The function of power system is to serve load.
We want to have,
For most of the time,
With least cost.
Generation > Load
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Three Areas of Reliability Analysis
1. Generating capacity reliability
Concern with generation adequacy
2. Composite system reliability
Consider both generation and transmission lines
3. Distribution system reliability
Local network connected to end-users
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Generating Capacity Reliability
1. Single-area reliability analysis All generators and loads are connected to a
single bus
2. Multi-area reliability analysis Generators and loads within area are connected
to a single bus
Consider tie-lines between areas
Limitation of intra-area transmission are included when determining inter-area transmission capability
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Single Area Reliability Analysis
Interest to find out the ability of existing generation to serve load
Single bus analysis
Generators and loads are within the same bus
Each generators has their own performance indexes
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Composite System Reliability
Concern with generation and transmission capability adequacy
High-voltage transmission lines
May include high-voltage transformers, circuit breakers http://www.powerworld.com/images/7-bus%20Oneline.jpg
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Multi-Area Reliability Analysis
Interest to find out if area generation or tie-line capability are adequate to serve load
Consider thousands of nodes then simplify the system to small workable nodes (areas)
Generator and load from different nodes within the same area are grouped into one.
Tie-line capability between areas
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Distribution System Reliability
Interest to find out the reliability level at load point
Network configuration/ topology
Analysis takes into account reliability of the following low-voltage components, Transformers
Circuit breakers
http://www.tpub.com/content/construction/14027/css/14027_63.htm
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POWER SYSTEMS RELIABILITY INDEXES AND CRITERION
Reliability indexes
Reliability criterion
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Power Systems Reliability Indexes
Deterministic indexes
Do not take into account the uncertainties that affect reliability
Simple calculation
Require less data
Probabilistic indexes
Reflect uncertainties in the system
Require failure statistics of the devices
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Deterministic Indexes
Operating reserve margin
Excess generation capacity in case of emergency
Percentage reserve
Amount of reserve capacity as a percentage of the total peak load
Reserve margin as the largest unit online
Amount of reserve equals to the capacity of the largest unit online
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Probabilistic Indexes
Loss of load probability Probability that generation will not meet demand
in a year
Commonly shown as number of hours/days. (by multiply LOLP by number of hours/days in a year)
Loss of load frequency How often does the system fail in a year
Expected Energy Not Supplied (EENS) or Expected Unserved Energy (EUE)
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Why need reliability criterion?
Develop standardized quantity
Planning and Operation purposes
To avoid catastrophic failures
Design problems
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Power Systems Reliability Criterion
Deterministic criteria
N-m contingency analysis
System with N components should be able to serve peak load when loss m components
Sometimes called security analysis
Probabilistic criteria
Loss of load expectation, for example, 1 day in 10 years
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Cost-Benefit Analysis
High reliability achieved with high cost
Is it worthwhile to have high reliability?
http://www.eppo.go.th/power/ERI-study-E/ERI-EOCS-1-E.html
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Summary
We know what reliability is
We know a bit about power system reliability
We need to know
Probability theory
Reliability theory
Random processes
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Reading Materials
Review basic probability theory
Random variables
Probability rules (addition, multiplication,
Conditional probability
Probability distribution functions
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