Technical Seminar On

Transformer Diagnostic By An Expert System

PRESENTATION BY :

GURURAJ BRAWOOR

OVERVIEW OF SEMINARObjectives Introduction Expert SystemTSI - Transformer Status Indicator

1.Environmental Parameters 2.Operational Parameters

Computation Method1.Linear Evaluation 2.Non-linear Evaluation 3.TSI Code And TSI Factor

Test Data Program And Results Of The Program Conclusion Bibliography

OBJECTIVES• The transformer is the most important equipment in the

transmission and distribution system.

• This expert system is the principle of condition based maintenance strategy. The system consider discrete diagnostical results.

• For the comparison we need to consider some other parameters what do not indicate the status of the insulation but it has influence for that.

• In the research work, the expert system tested by real data from the Hungarian distribution system. The source of the testing data is 13 HV/MV distribution transformers in Hungary.

• The average age of the transformers is 25-30 years, more than the planned lifetime.

• It is not necessary to change these equipment's only because of their age.

• The Operators have to know and manage more information about the insulation, because this is determined the expectation time.

• There is a lot of parameter what affect the status of the insulation (loading, oil parameters etc).

• The Transformer Status Indicator (TSI) expert system considers the essential parameters (environmental influences, operating values and diagnostic results) to gives the status of the insulation.

INTRODUCTION

• The TSI is a computer aided expert system.

• The expert system provides a technical and economic evaluation and comparison by means of only two numbers, the TSI factor and its reliability.

• These introduces the advantages of Transformer Status Indicator (TSI) expert system and present the results for 13 HV/MV transformers.

CONTD…

• An expert system is computer software that attempts to act like a human expert on a particular subject area. 

• Expert systems are often used to advise non-experts in situations where a human expert in unavailable (for example it may be too expensive to employ a human expert, or it might be a difficult to reach location).

What is an Expert System?

How Do Expert Systems Work?An expert system is made up of three parts:

A user interface - This is the system that allows a non-expert user to query (question) the expert system, and to receive advice. The user-interface is designed to be a simple to use as possible.

A knowledge base - This is a collection of facts and rules. The knowledge base is created from information provided by human experts.

An inference engine - This acts rather like a search engine, examining the knowledge base for information that matches the user's query.

Where Are Expert Systems Used?• Medical diagnosis.

• Playing strategy games like chess against a computer.

• Providing financial advice whether to invest in a business, etc.

• Helping to identify items such as plants / animals / rocks / etc.

• Helping to discover locations to drill for water / oil.

Can Expert Systems Make Mistakes?

Expert systems have some problems

• Can't easily adapt to new circumstances (e.g. if they are presented with totally unexpected data, they are unable to process it).

• Can be difficult to use (if the non-expert user makes mistakes when using the system, the resulting advice could be very wrong).

• They have no 'common sense' (a human user tends to notice obvious errors, whereas a computer wouldn't).

TSI-TRANSFORMER STATUS INDICATOR

• To make a computer aided evaluating for the transformers an expert system was developed at the High Voltage Laboratory of the Budapest University of Technology and Economics.

• The goal was to mark the status of a transformer only one number for the technical and economical comparison.

• The name of this expert system is Transformer Status Indicator (TSI), the result number is the TSI factor and its reliability.

• In the evaluation the expert system is considering the electrical-, mechanical- and chemical parameters in two groups; operational and environmental parameters.

CONTD…

A. Environmental parameters: - Exterior and auxiliary equipment’s quality - Age - Maintenance history - Geographical data - Location in the grid

B. Operational parameters: - Dissolved Gas Analyzing (DGA) - Oil test - Recovery Voltage Measurement (RVM) - Operational history (loading) - Insulation resistance - Furan content - Thermograph (infrared camera)

COMPUTATION METHOD Linear evaluating system • The considered parameters (physical effects) have one or

more physical values (PV). The PVs are the measurable values, for example the breakdown voltage of the oil.

• A weight factor (Wi) assigned for each PV because the PVs causes variant degradation in the insulation.

• Because of the variant scale of the PVs we need to use a Classification Value (Si) in the computing method.

• The value of the Si is between 0-1 according to the higher

and lower limit of the PV .

Example for the breaking points of the characteristics for thermograph.

• A non-linear method is combining the diagnostic factors and it may be beneficial.

• In case the results reveal that a critical system is failing, the system should calculate a health index that approaches zero, however when no critical condition exists, it should observe the weighting of the parameters.

• The system should additionally enable new diagnostic methods to be easily incorporated.

Non-linear Evaluation

Non-linear (bottom) and linear (top) combination of critical parameters.

TSI factor The output of the expert system is the status of the insulation. This number is the TSI factor. The TSI factor can be calculated by using a TSI code and TSI weights (Ki).

TSI code Now the TSI expert system is using the linear evaluation method for computing the TSI factor. The typical equation for calculating the TSI Code.

TEST DATA

TABLE IV. AVALIABILE DATA FOR A TRANSFORMER

PROGRAM

• For the presented evaluating method and for the necessary data storage, a program was developed.

• The program handles the basic data (transformer ID, manufacturing number, substation name and place, type, nominal voltages) and the diagnostic results too, of the transformers.

• The program provides an evaluating in the necessary time period and displays it.

• It is very important to prepare the program to connect or can be integrated into a company asset management system to download the diagnostic results and upload the evaluating results.

RESULTS OF THE PROGRAM

• The status of the insulation is represented by the TSI factor (TSIF).

• It contains the ageing phenomena and other necessary information for the evaluating.

• With these information’s the TSI expert system serves the conditional based maintenance strategy in the asset management system.

Diagram of a transformer evaluation between 2000-2011

There are some relevant evaluating parameter.

• Measured and calculated degradation speed (average)

• Increased TSI represents the reconstruction (time and volume).

• Fault level (calculated by statistical data).

• Increased lifetime (expectation of life).

Using these useful information’s the operator can plan the reconstruction or maintenance of each transformers.

• The TSI factor gives a reliability volume of the status of the transformer and its insulation system.

• The TSI support the condition based maintenance strategy, so it helps for the operators to select the indigent transformer to get maintenance or a reconstruction while minimized the cost of the asset management.

• Further research needed the evaluation and have to evaluate more

transformers to get suitable information’s and statistical result for the failure level.

• The other task is to improve the physical effect evaluating (e.g.: RVM or dielectric loss factor or DGA using other research work results.

CONCLUSION

• Cs. Vörös, B. Németh, S. Szabó, I. Berta, Diagnostic evaluation of power transformers by an expert system, International Symposium on Electrical Insulation, Puerto Rico, 2012,

• Cs. Vörös: Evaluating the transformer diagnostic results according to Health Index “Transzgormátor diagnosztika kiértékelése Health Index alapján”.Budapest University of Technology and Economics,2010.(in Hungarian language)

• Csaba Vörös, Bálint Németh, István Kiss,Transformer Status Indicator (TSI) as a new expert system for integrating the diagnostic results of power transformesr, International Youth Conference on Energy (IYCE) 2011, Portugal

• http://www.igcseict.info/theory/7_2/expert/

BIBLIOGRAPHY