1. Barcelona, May 14, 2003 Session 5; Block 1; Paper 5
Maintenance Strategy using the Fuzzy-logic for medium voltage Switchgear and Substations by
G. Balzer, Darmstadt University of Technology A. W. Heiß O. Schmitt, ABB Utilities GmbH
It is a great honor for me, to make a contribution related to new approaches of maintenance strategies.

2. Final result of the assessment20 40 60 80
100 10 30 50 70 90 c i
EHSN-307
SHAF-299
POHL-301
HOHA-601 B C
condition
replacement A dC dA
service dB
The final result can be seen from this figure. The importance is listed on the x-axis, whereas the y-axis represents the condition, as explained before. The most important substation is no If we look at the replacement area, the ranking of the substations in the red area should be B - A - C, according to the line length of the axis d.
importance d
Final result of the assessment

3. Main principle of the Fuzzy-Logic approach for renovation strategy
If item A is in condition cA and item B in condition cB,
then the result is E
In terms of e renovation of a substation:
If the building as well as the primary equipment are in a poor condition ,
then a total renovation of the installation is advisable.
The last feature, which I want to explain, is the usage of artificial intelligence to perform a renovation of a substation
In order to identify which maintenance measure is best suited for a renovation, the analysis will not only be founded on "objectifieable" criteria, such as condition and importance of the installation, but also on empirical operating data that has been collected over many years. A renewal of an aged installation, for instance, may also require that the surrounding building be replaced.
In a solution concept using fuzzy logic, the response of the solution is first described by linguistic “If - then” rules, as:
If the building is in poor condition and the primary equipment is in poor condition,
then a total renovation of the installation/station is advisable.
Main principle of the Fuzzy-Logic approach for renovation strategy

4. Basic principle of a decision-taking process using fuzzy logic
Rules
Output values
Input values
Knowledge processing
Fuzzification
Defuzzification
The basic principle of the fuzzy process can be seen from the next figure.
We have the input values, which is in this case the result of the condition assessment of the equipment. Furthermore there are certain rules, which describe the relationship between the input and the output values.
The next transparancy shows the final result of the fuzzy process.
Basic principle of a decision-taking process using fuzzy logic

5. What is the result of the assessment of a complete substation:
- we can compare several substations
- we can see, which equipment of the substation will influence the condition of the asset.
And this will lead to the result, if the complete substation should be replaced or only some equipment if possible.
Rules for determining the fuzzy-step: building/tower - primary equipment P poor M medium G good

6. Implementation of a maintenance strategy for substations
This figure shows the strategy process for the secondary substations. It can be seen, that the change of the transformer is independent on the condition of the other equipment. In a first step, we consider, if the total substation will be removed depending on the condition of the building and the primary equipment. The second step is responsible for the evaluation, if the complete primary equipment will be replaced or the single items.
Finally certain system issues has to be considered, for example, if a change in the system voltage is applied in the next year and so on.
The result of the fuzzy process is, how many substations have to be replaced completely or only the equipment, which are in a poor condition.
Implementation of a maintenance strategy for substations

7. System issues
- Is this a optimal location of the substation, regarding power loss?
- Are there plans to change the voltage range?
- Will be a change from overhead line connection to cable?
- Are the any problems from a public point of view?
- Are there any changes regarding the technical requirements (capacity, reliability, customer requirements, etc.)?
What are the main points I want to stress:
First I say something concerning the age profile of some equipment and the consequence of ageing.
The main point is dealing with maintenance strategies and in special the Reliability Centered Maintenance.
Finally I shall mention some aspects and possibilities of artificial intelligence and risk assessment.

8. Evaluation of 40 stations (number of components to be replaced):
- total substations: 9
- primary equipment: 1
- building 5
- switches 4
- transformers -
It makes sense to include this procedure in a computer program.
What is the advantage of the computer aided assessment:
- we have fixed criteria for the assessment
- we get a ranking of the equipment and
- we have a documentation of the result.
This is my final conclusion and I hope that I was able to convince you of the advantage of the Reliability Centered Maintenance and the complete Asset Management process.
Many thanks for your attention.

9. Advantage of a the Fuzzy-Logic assessment:
- fixing of compulsory criteria
- decision: renovation of the complete substation or single items
- documentation of the decision
It makes sense to include this procedure in a computer program.
What is the advantage of the computer aided assessment:
- we have fixed criteria for the assessment
- we get a ranking of the equipment and
- we have a documentation of the result.
This is my final conclusion and I hope that I was able to convince you of the advantage of the Reliability Centered Maintenance and the complete Asset Management process.
Many thanks for your attention.