Statistical Analysis of Power System Faults  May99-15 Senior Design Project

Contents of this Page:
Abstract
Problem Statement or Background or Context
Design Objectives
Proposed Technical Solution
Proposed Budgets
Proposed Schedule

Abstract

With the beginning of deregulation and its effects being felt throughout the power production and transmission system a new way of power line loading needs to be considered.  With the current market pressure that is slowing down and even halting new transmission construction severely limiting the utilities access to wheeling large blocks of power.  So the current conservative values of line maximums needs to be reconsidered to determine if a new standard can be chosen to increase line loading.  With the issue of open access it has come to be more important then ever to assess risk in overloading the power transmission system.  As a senior design project the answer that needs to be addressed is simple: “How can statistical knowledge of risk, effect the amount of line loading a utility will assume?”

Problem Statement or Background or Context

The project is seeking the statistical value of the expected consequence “risk” associated with the thermal overloading of an overhead conductor on a transmission line.

Design Objectives

Electric utilities use transmission lines to move power from the power plants to the consumers and other utilities.  This transfer of power is commonly known as load flow, which is directly proportional to current flow.  Overloading of a transmission line can be caused by weather, outages of parallel lines, unexpected load growth, and unwillingness of the electric utility to build transmission lines.

1 Causes of Overloading

1.1 Weather
The summer is a crucial season for the utilities.  During the summer the load increases due to the operation of air conditioners and the heat from the summer sun on the overhead conductors.

1.2 Outages
 Outage of power lines, whether it is due to maintenance or weather related causes, can cause excess loading in other lines nearby.  This problem is compounded in the summer.

1.3 Load Growth
New industrial customers often require more power than they initially requested, leading to the over loading of the lines that feed them.

1.4 Deregulation
On April 24, 1996, FERC (Federal Energy Regulatory Commission) issued orders 888 and 889, which encouraged wholesale competition.  The objective of these two orders is the elimination of the monopoly in the transmission of electricity.  Due the uncertainty of open access, utilities are becoming more unwilling to build new transmission lines.   With this lack of new construction, a rise in loading of the transmission grid is a certain cause for alarm.

These are reasons why utilities are reconsidering their stance on how to load the transmission lines.

2 Problems
2.1 Constraints
The most common constraint that limits the capability of the transmission line is the thermal rating of the conductor.  Thermal rating for a conductor depends on the current flow and the ambient weather conditions, such as temperature, wind speed, and wind direction.

2.2 Conservative Values
The current method is to use highly conservative values chosen in an era when transmission access was not a problem and transmission wheeling on a large scale was unheard of.  With these factors in mind the old conservative method of following the worst case scenario.  Currently thermal rating for a conductor depends on the maximum current that the conductor can sustain at some ambient temperature.  Since weather is an uncertain factor, the current calculation of thermal rating is an approximation.  This conservative method results in the under-utilization of conductors and can be improved by probabilistic methods.

2.3 Thermal Risk
When operated above thermal rating, damage to the conductor become a concern of the power engineer.  The risk of exceeding the thermal rating of a conductor depends on time.  The longer you sustain a current level over the rated value, the greater the risk.  Thermal risk is the product of the probability that the conductor is being operated over it’s rated temperature and the consequences of operating beyond the rated temperature.

3 Consequences
3.1 Damage to the Conductor
The consequence is the damage to the conductor. One impact of exceeding the thermal rating is loss of ground clearance due to sagging.  This problem occurs when conductors expand and sag into objects such as tree, under-built lines, and other foreign objects leading to fault conditions.  The second consequence is loss of tensile strength due to annealing the recrystallization of the metal.  This reduces the life of the conductor.  Replacement of the conductor and power outages is costly to the electric utility and their customers.

3.2 Lost Time and Money
When all of these factors add up to a failure the end result is lost time and money on both the producer and consumer.  When a customer is without power the utility faces stiff public relations losses.  Along with the loss in public relation, there is the loss of revenue in both repairs and losses in sales.

Proposed Technical Solution

1 Proposed Solutions
During the process of determining the best route to finish this project on time and with the most chance for success, our group has come up with four options to choose from.   These options include: Keeping the original code as is, changing the graphical user interface (GUI), rewriting the user interface in JAVA, or starting from scratch with new code.  The following sections will briefly describe each option giving the pros and cons for each idea.

1.1 No Change
The first option of leaving the code as is would seem at first to be the easiest route to take in this assignment, but the code is full of holes and the user interface is not easy to use.  Another problem with maintaining this code is that most utilities do not have MATLAB capabilities to run the program.  This provides a challenge to provide this software to the most users.

 The original code is also lacking easy instructions to use it.  The GUI also has major flaws when trying to run the program as is.  The code has a few bugs in it and if these are not worked out they will provide problems to the subsequent users and possibly give the wrong answers and conclusions concerning the safe operation of the power system.

Along with all these negative characteristics, this option also does not provide for the use of historic data.  Our intent is to provide historical weather data and give meaningful statistics to be used when this program will be run.  This option will not provide for our clients’ needs or there wants.  So this option will not be chosen.

1.2 Change Graphical User Interface
 

1.3 Use JAVA for MATLAB Interface
The version currently in use will not allow the user to access it over the Internet.  The idea of building a JAVA link will allow utility companies access to the program via the Internet.  The current MATLAB code will make the use hard for many companies because of not owning the program.  By writing the JAVA code to link the MATLAB engine to the Internet will allow any utility company use if they have access to the Internet.

The problems associated with producing this kind of program are the lack of actual Java experience in the group.  We think however that because of JAVA’s familiarity with C the learning curve should be short.

The pros of using the JAVA interface are many:

• Access to the internet
• Ability to use historical weather records for weather statistics.
• Allow multiple users without having to purchase MATLAB’
• Design a more user friendly front end

2 Chosen Solution
The solution path that our group has chosen is to rewrite the Graphical User Interface (GUI) in JAVA.  The selection of this path will enable our group to improve the presentation of the software and allow many users over the Internet that would not normally have the opportunity to use this software.  The reasons for this decision are as follows:

• Internet use
• Redesigned user interface
• Maintains MATLAB engine for number calculations
• Increases functionality
• Can be achieved in two semesters of work

Proposed Budgets
 

Phase/Task	Effort(Hours)	Cost($)
Web Site	25	0
Project Plan	30	3
Poster	60	40
Oral Presentation	40	10
Design Review	100	3
Research	100	3
Sub Total	355	59

 

Phase/Task	Effort(Hours)	Cost($)
Web Site	30	0
Progress Report	10	3
Coding in Java	200	0
Final written report	100	3
Final Oral report	50	10
Sub Total	390	16

 

Grand Total

745

75

Proposed Schedule
 

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