Computer Program RCM - Overview

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ABSTRACT. The paper deals with the computer programme RCM – software tool for Reliability Centered Maintenance (RCM) and description of software for this ...
ELECTRIC POWER ENGINEERING 2009

Computer Program RCM - Overview Vladimír Král1), Radomír Goňo2), Stanislav Rusek3), Tomáš Raška4) 1-3)

VŠB-TUO, Department of Electrical Power Engineering, 17. listopadu 15, 708 33 Ostrava-Poruba, http://fei1.vsb.cz/kat451 4) ČEZ Distribuční služby, s.r.o., 28. října 3123/153, 709 02 Ostrava, Moravská Ostrava, http://www.cez.cz 1) tel: +420 59 732 4421, email: [email protected] , 2) tel: +420 59 732 4554, email: [email protected] , 3) tel: +420 59 732 4377, email: [email protected] , 4) tel: +420 59 667 3591, email: [email protected]

ABSTRACT The paper deals with the computer programme RCM – software tool for Reliability Centered Maintenance (RCM) and description of software for this maintenance optimization used for electric distribution network devices. Logic of the software is based on the reliability centered maintenance principles. Its aim is more effectively maintenance schedules of equipment. Program connects two approaches optimal maintenance interval and equipment maintenance order according condition to the one software. The inputs are databases of outages, maintenance, equipment condition and financial flow. Created program works on databases of real energy company. Furthermore the developed software seems to be useful in the various industry branches. Keywords: Maintenance, Database, Software, Electrical distribution system

1 INTRODUCTION At the Department of Electrical Power Engineering at VŠB-Technical University of Ostrava we have already been concerned with the development of methodology and software for reliability centered maintenance since 2004. RCM is a term that appeared in the area of electrical power engineering as late as the nineties of last century. The goal of RCM is to shorten maintenance-based outages of pieces of equipment to ensure the given reliability. Thus it is a case of the principle of maintenance depending not on time but on the real state of the item of equipment. RCM is a decision-making tool that makes it possible to control or improve the maintenance schedule. RCM may make the existing maintenance schedules more efficient and optimized. RCM is based on the assumption that reliability is a constructional characteristic that is implemented and maintained in the course of operation. At our Department of Electrical Power Engineering at VŠB - Technical University of Ostrava we have already been concerned with the development of a methodology for RCM for some years. Our main objective is its practical utilization and inclusion into the system of maintenance of the electrical power company. On that account are developed algorithms and calculation procedures for individual components of the distribution network.

2 AIM OF THE RCM SYSTEM We chose two basic approaches to RCM implementation in the framework of distribution power networks. One approach leads to the optimization of the maintenance cycle for all components of the given type or groups of components of the same type. The other approach leads to the optimization of condition based maintenance (on-condition maintenance), i.e. to the determination of optimum order of maintenance of particular components of the same type. The goal of reliability centered maintenance is to formulate such a maintenance strategy so that the total operating costs may be minimized at keeping the necessary degree of the reliability, safety and environmental soundness of equipment operated. Virtually for the first approach it means that for each item of equipment the equation of total operating costs will be formed and its local maximum will be searched for and comparison of condition and importance of components for the second approach should be done.

3 CONCEPTION OF THE PROGRAM Basic conception matches principles described above. Software logic is based on the principles of RCM [1]. By means of the software, the maintenance schedule for equipment should be more effective so that the given reliability could be guaranteed. The input is formed by the databases of outages, maintenance, conditions of equipment and financial flows. The output is either the optimum maintenance interval for the group of items of equipment, or the order of items of equipment according to importance and condition. Because the RCM system utilises many information sources and optimise the maintenance of several thousand components, it was necessary to design a right and transparent data structure of all inputs. Input data for the program are reading from the exports from databases of the real distribution company. The program will deal with the application of RCM for both the approaches to RCM implementation. The approaches will be applied according to a specific component of the distribution network. The comparison of the approaches is as follows: - optimization of the maintenance cycle - the number of components of the given type is high; generally, each component of the given type has low importance, costs of the specif-

ic component of the given type cannot be obtained, at the analysis of the event (failure, outage) the specific component cannot be found, - determination of the order of components for maintenance - the boundary must be defined from when performing maintenance is reasonable not only from the economical point of view, equipment monitoring is possible (e.g. on-line monitoring), we must be able to determine the condition and importance of equipment.

4 PROGRAM RCM The RCM software is developed in Microsoft Visual Basic (VB), therefore other very important criteria is easy manipulation and processing input and output data in this development system. VB is the basic Windows developer's tool that enables the rapid and cheap creation of applications. The programs developed in this environment they are fully compatibles with all Microsoft Windows operating systems. Program is an “offline” version now (input data for the program are read from the exports from databases of the distribution company), on which the functionality of all calculation algorithms are verified and the program may be completely debugged. The final version will be handed over to the distribution company that will ensure the implementation of this program into the existing information system. 4.1 Block Diagram of the Program The block diagram of the program is given in Fig. 1. The basic inputs are databases of the distribution company (technical information system - TIS and financial information system - FIS), from which required data will be read. The inputs, which will be entered by the program operator, are mainly criteria for the determination of the condition of the component (weights of particular influences) and criteria that will serve the determination of importance of particular components. Furthermore, control on the part of authorities must be taken into account, such as penalties imposed for not obeying the standards prescribed for electricity supplies. For the first group of types of components the output of the program is the optimum maintenance cycle, for the second group of types of components then the optimum order of performing maintenance (coordinates of components depending upon the condition and importance of them). TIS

FIS Regulations

Importance

Criteria

RCM Program

Coordinates of the piece of equipment Optimum maintenance cycle

Fig. 1 Block diagram of the program

4.2 Structure of Input Databases The structure of input data will depend on the type of the component. According to it, the program will determine the approach to RCM - optimization of the maintenance cycle or determination of the order of components for maintenance, and the structure of input data. The input data will be then read from relevant databases. Input Data for Maintenance Optimisation

The input data required for the basic RCM conception of this approach is given by input data for the cost function. The structure of this data is based on the structure of the cost function. At first sight, the input data is very simple and available. However, from a more detailed analysis it follows that acquiring correct data for the cost function has many difficulties. The main problem consists in the fact that for the total analysis (that, however, is out of the question) it would be necessary to know the given values for each separate element (not the type of the element). Also with reference to the fact that any “importance” cannot be assigned to any specific component (neither FIS, nor TIS divides data up to a specific piece of equipment), it is necessary to proceed to data division into groups. Then, maintenance intervals of the groups will be different. Input data for the division of components into groups by importance are as follows: - for all components of the given type - coefficient for consumer evaluation, the number of groups for division and their limits and the type of component, - separately for each component - identification number, the number of connected consumers by type, possible another division of the component. The result of the division of components into groups by importance is the determination of the amounts of components in particular groups and the assignation of a group number to each component. Even this division is rather inaccurate because the failure rate of the element may also depend on the element “load”, i.e. on the element position in the network. Likewise, the repair and maintenance costs may depend on e.g. element accessibility with regard to technical facilities, i.e. on the element location as well. At the very accurate analysis all input data should be considered to be dependent both on the type and the location of the element in the network. Input data for the RCM analysis itself are maintenance costs, repair costs, failure rate, total time of failures, time of scheduled outage, number of all consumers, including their types, number of outages at not obeying the standards, penalties, price of undelivered electrical energy for specific types of consumers, relationship between costs of undelivered energy by particular types of consumers, relationship between costs of outage by specific groups, maintenance rate and the average power passing through the given component. The given data are related to the period under consideration of one year. Sources of these input data are exports from technical records, failure databases and financial databases, or the data are entered directly by the keyboard and are stored in a special file.

On-Condition RCM Input Data

The structure of input data depends on the specific component. Generally, they may be divided into the following three groups: - Identification of the specific component. - Data determining the condition of this component. - Data determining the importance of this component. 4.3 Data Interface Requirements The actual design of the data interface structure and format starts from these, sometimes quite antagonistic, requirements. The most important are: • compatibility with different operating systems, • expand and availability of tools in which these data can be processed (software), • speed of data access, • possibility of export from the existing information systems of distribution companies, • off-line interconnection, but also readiness for direct access into the existing information systems. At the very beginning we rejected export and processing data files due to their bad arrangement in case of more elaborated and complicated structures. Moreover, it would be also unsuitable to use the binary data formats structured with respect to the data itself or the development system. For the reasons stated bellow, we have also abandoned purely database formats. Finally, the optimum way seems to be a combination of the Microsoft Excel and Access tables. Using only Access databases was not possible due to indefiniteness of some input data - the input may be a number, as well as a text “variant variable”. 4.4 General definitions, rules Inputs in Excel format are used in cases where there is further editing possible. Access format are used in cases where this sort of access can dramatically accelerate data processing. A typical example is information retrieval, for which in SQL language is used. In Tab. 1 are all kinds of data formats used in input / output databases. Tab. 1 The list of data types Identification

Data type

Number of bytes

integer

integer

2

long single double boolean string string (X) variant date

integer (double accuracy) decimal number decimal number (double accuracy) logical value string of variable length string of fixed length general (number and string) date in international format (d.m.y.)

The number of bytes is given in Tab. 1 only because the length of the given data type in Visual Basic may be different from another programming language. 4.5 Real Information System of Distribution Company The structure of new information system is shown in Fig. 2, where: SAP TR/GIS

One-way data transmission

TIS

Report

Job order

Costs

Fig. 2 Structure of information system •

TR/GIS is technical register / geographic information system. It includes all attributes of all registered components. • TIS is technical information system, which includes original previous TIS, FIS and CIS (consumer information system). • Report is SAP data object. There are produced cards of failure, outages and breakdown demand. • Job order contains costs linked with the performance of work, material and services. Some of them items are better to analyze on SAP system and results import to RCM program. The Interconnection is possible via data interface. Both data interface and interconnection to IS are described in [2] and [3].

5 DESCRIPTION OF RCM PROGRAM The input screen is presented in Fig. 3. There are the basic menu, program name and program version in this figure.

4 4 8 1 10+length of the string length of string (X) 16 / 22+ length of string 8 Fig. 3 Input screen of program

In the next Fig. 4 there is the selection of a kind of equipment, for which the analysis is being made. After selecting the component, a relevant algorithm is then activated - the optimization of maintenance cycle or the optimization of the order of components by the condition and importance of them.

optimum order of components for maintenance is then determined.

Fig. 6 Results of DTS – cost curves

Fig. 4 Selection of analyzed kind of equipment Input Screen of Maintenance by Condition and Importance for circuit breakers 110 kV is in Fig. 5. Technical conditions, evaluation of diagnostic tests, weights of particular influences and importance are in MS Excel input format. Editing of all inputs is possible.

Fig. 7 Results of maintenance by condition and importance

6 CONCLUSION

Fig. 5 Weights of particular influences 5.1 Results screens As an example of using the cost function the application to the distribution transformer substations (DTS) was chosen. The result of optimization of the DTS maintenance cycle is a cost curve for DTS particular groups shown in the Fig. 6 On the basis of this curve; the optimum value of maintenance rate that is given in the lower part of the screen is then mathematically determined. As an example of application of RCM by condition and importance the power switch in the 110 kV substation was chosen. The result of RCM by the determination of optimum order of maintenance is a graph in the Fig. 7 with the layout of particular pieces of equipment. On the basis of this graph, the

The contribution describes the third version of the program RCM designed for the optimization of maintenance of equipment of the distribution system. Application supports basic data for responsible and logical decisions about the area of maintenance and basic data for the preparation of an effective maintenance schedule and the creation of a feedback system. The program is being developed with the aim to be universal, so that it may solve both the approaches - the optimization of the maintenance cycle and determination of the order of components for maintenance. All variables of the program may be entered from input databases and edited by means of the keyboard. ACKNOWLEDGEMENTS

This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic (No. CEZ MSM6198910007).

REFERENCES

[1] Skog, J. 1999: Maintenance Task Interval Determination. Maintenance and Test Engineering Co. USA. [2] Rusek, S., Král, V., Goňo, R., Raška, T.: Software RCM – an Optimization Tool for the Maintenance of Electric Power Network Devices. In 6th International Scientific Conference Electric Power Engineering 2005, Kouty nad Desnou, Ostrava: VŠB-TU Ostrava, 2005, 10 p., ISBN 80-248-0842-0. [3] Král, V., Rusek, S., Goňo, R., Raška, T.: Software RCM – data interface. In 8th International Scientific Conference EPE 2007, Kouty nad Desnou, Ostrava: VŠB-TU Ostrava, 2007, 10 p., ISBN 978-80-248-13912. [4] Rusek, S., Goňo, R., Král, V. 2006: Application of Reliability Centered Maintenance in Electricity Distribution Company. IASTED International Conference PEA 2006, p. 96 - 101, Gaborone, Botswana.