system reliability

EE5712 Power System Reliability:: Introduction

Panida Jirutitijaroen

1EE5712 Power System Reliability 12/27/2010

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]

Outline

About this class

Introduction to reliability

Basic steps in system reliability analysis

Introduction to power system reliability

Power system reliability indexes and criterion


ABOUT THIS CLASS

Overview

Assessment

Scope

Objective


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.


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.


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.


Scope

Power System Reliability

Electric power

System

Reliability

Reliability theory applied to power systems

Analytical and simulation tools to conduct reliability analysis


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


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.


INTRODUCTION TO RELIABILITY

What is reliability?

What causes a system to fail?

How to model uncertainties?


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?


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


Example 3: Non-Identical Transmission Lines


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


Example 4: Identical Generators


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


Example 5: Non-Identical Generators


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


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?


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


What causes a system to fail?

Human factors

System design

Operation condition

Maintenance procedure

Deterioration (function of time)

Random failures

Uncertainties


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


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


Example 5: Identical Generators

If each system has the following level of reliability and cost


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


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


BASIC STEPS IN SYSTEM RELIABILITY ANALYSIS

Objective of the analysis

Component modeling

System modeling

Performance function

Reliability Evaluation


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


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


Observation of A Component


Time

Z(t)

0

1

2

Time

Z(t)

0

1

2

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


Need to know how each device causes a system to fail!

Performance Function

To evaluate system reliability

Recall,

Need to define intended function

Ability of a system to perform its intended function


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


INTRODUCTION TO POWER SYSTEMS

Functional Zones in Power Systems

Objective of Reliability Analysis

Levels of Reliability Analysis

Power System Reliability Indexes


Functional Zones of Power Systems

Generation system

Generators

Load

Transmission system

High voltage transmission lines

Distribution system

Low voltage transmission lines

End users


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)

33

Generation Capacity in Singapore

34

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

35

36

North American Electric Power Connections

http://www.nerc.com/regional/NERC_Interconnections_color.jpg

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

37

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

38

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

Singapore Electric Demand

Peak demand in 2007 is 5946 MW. Electricity demand in 2007 is 41134 GWh. 39

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?

40

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


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


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


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


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


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


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


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


POWER SYSTEMS RELIABILITY INDEXES AND CRITERION

Reliability indexes

Reliability criterion


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


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


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)


Why need reliability criterion?

Develop standardized quantity

Planning and Operation purposes

To avoid catastrophic failures

Design problems


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


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


Summary

We know what reliability is

We know a bit about power system reliability

We need to know

Probability theory

Reliability theory

Random processes


Reading Materials

Review basic probability theory

Random variables

Probability rules (addition, multiplication,

Conditional probability

Probability distribution functions


system reliability

Documents

reliability measures2

large system

small system

multiarea reliability

reliability basic steps

basic reliability concepts

lec composite system

power systems analytical