RCM Application for Turkish National Power Transmission System Aydogan Ozdemir
Elif Deniz Kuldasli
Department of Electrical Engineering Istanbul Technical University Istanbul, Turkey
[email protected]
Engineering Department AKSA Power Generation Corporation Istanbul, Turkey
[email protected]
different industries [1-6]. RCM is a systematic risk based maintenance procedure for achieving cost-effective maintenance plans. RCM can briefly be thought as the mixture and synthesis of reactive, periodic and predictive maintenance applications.
Abstract— This study presents a RCM program for Turkish National Power Transmission System. Depending upon the information from transmission utility staff, the system is decomposed into functional blocks and failures for each functional block is held individually to attain a reasonable maintenance program for the transmission system.
The traditional regulated electric power industry has been changing to a competitive environment that requires reducing overall costs while maintaining desired reliability level. One of the largest costs of an electric utility is the operation and maintenance costs of energy delivery systems. RCM is the most powerful tool which organizes the maintenance issues according to the impacts of equipment failure on system reliability.
Keywords-RCM, failure mode, preventive maintenance, predictive maintenance
I.
INTRODUCTION
Industrial facilities require appropriate management processes for a sustainable survival in today’s competitive economical conditions and industrial/technological developments. The investment is not only the requirement of a reliable process planning, production and sales, but also it is an indispensable need of the maintenance management processes in order to achieve efficient, high-quality and continuous production scheme.
This study, proposes a new RCM based maintenance procedure for Turkish National Power Transmission System. With respect to the information obtained from national power transmission system authority, power transmission system is first divided into sub-systems. Failures of those sub-systems are later defined together with their prospective reasons (component failure modes resulting sub-system functional failures) and failure consequences. Decision tree diagrams of the sub-systems are constructed and RCM management program is developed by deriving the most appropriate maintenance procedures from the decision tree diagrams. In addition, several test and inspection techniques that can be used for predicative maintenance procedure are illustrated.
Reliability, defined as the ability of an entity to perform its function under designed operating and loading conditions. Although it is a matter of the design step of, sustainable reliability is closely related with the maintenance phase during the operational life of the units and systems. Preserving system reliability is almost impossible without an effective maintenance procedure. Maintenance investments in industry resulted in improved and more effective maintenance activities. Initial maintenance activities employed in 1930s were reactive maintenance actions. High costs of reactive maintenance process were the main reasons of a new concept called periodic maintenance. Following the application of periodic maintenance procedure, a new idea of “estimation of the failure before its existence” was one of the most important development in maintenance applications. This idea brought a new maintenance procedure known as predictive maintenance. The most important feature of the predictive maintenance process is the methodology used to estimate the failure before it occurs with the predictive testing and inspection tools.
II.
TURKISH NATIONAL POWER TRANSMISSION SYSTEM
Reliability issues and reducing Operation and Maintenance (O&M) costs are one the most important tasks of electric utilities. In an increasingly competitive power delivery environment, electric utilities are forced to apply more proactive methods of utility asset management. Power system component health is of utmost importance because revenues are affected by the condition of the equipment. Old and unhealthy equipments can result in service interruption, customer dissatisfaction, loss of good will, and eventual loss of customers. An effective maintenance strategy is essential to delivering safe and reliable electric power to customers economically.
One of the latest developments in maintenance era is the reliability centered maintenance, RCM. It was first originated in avionic studies at late 60’s and later adopted to several 978-1-4244-5721-2/10/$26.00 ©2010 IEEE 143
PMAPS 2010
Power transmission systems starting from generation substations up to distribution ones, are very important from the point of system reliability. Basic parts of Turkish National Power System are [7]: ¾
380 kV power transmission lines and cables,
¾
154 kV power transmission lines and cables,
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66 kV power sub-transmission lines and cables,
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380/154 kV auto-transformers,
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380-154 kV/distribution voltage power transformers,
¾
The remaining equipment used for the interconnection, measurement and protection issues.
TABLE III. TRANSFORMER AND SUBSTATION MAINTENANCE PERIODS Component of transformer sub-system Transformer Tank Oil Bushing Cooling system Control and maintenance of the connections Winding insulation Control of bolts, sealing rings etc Control of substation central busbar and its insulators.
TABLE IV. CIRCUIT BREAKER SUB-SYSTEM MAINTENANCE PERIODS
Turkish National power System is observed and controlled from a central National Electric Power Dispatch center and 8 regional power dispatch centers. Table 1-2 illustrate power transformer and power transmission line information.
Component Control and greasing of movable parts (normal environmental conditions) Control and greasing of movable parts (dirty and dusty environmental conditions)
The first step of RCM application is the identification of sybsystems. According to data collection scheme of the utility, power transmission system components are classified into three functional zones from failure and maintenance point of view. These subsystems are; ¾
Transformers
¾
Power Transmission Lines
¾
Switching Systems (only SF6 circuit breakers are thought at this first study)
66 kV TOTAL Total Total Number Power Number Power (MVA) (MVA) 57 672 1173 82056
TABLE II. TRANSMISSION LINES/CABLES IN TURKISH NATIONAL POWER TRANSMISSION SYSTEM. (2007) 220 kV 84.5
154 kV 31383
66 kV 477.4
X
In this study, we have constructed the information forms with respect to the information obtained from the failure data collection scheme of National Power Transmission Authority of Turkey. In this first attempt functional failures for the subsystems are defined as:
POWER TRANSMISSION SYSTEM TRANSFORMERS IN TURKISH NATIONAL POWER TRANSMISSION SYSTEM. (2007)
Voltage Rating 380 kV Length[km] 14338.4
X
Failure modes are component-specific failures that may result in the functional failure of the subsystem. The relation between functional failures and subsystem failure modes are very important for the determination of the maintenance procedure. Therefore, component failure modes, their effects and also consequences of the failures must be known. These definitions, relations and consequences together are used to obtain information forms for the subsystems. It is obvious that improved information forms are the way of achieving costeffective RCM procedure.
Power transmission line maintenance and control periods are taken according to manufacturer specifications or to relevant standards. The lines are checked for the adequacy of their inclination, the distance to the trees and to the buildings, the condition of the joints, the condition of the connectors, connections to the insulators along the total line route. In addition insulators are checked by insulation control devices once at each 5 years.
380 kV 154 kV Total Total Number Power Number Power (MVA) (MVA) 153 28715 963 52669
Maintenance period 6 months 12 months
Following the subsystem identification, functions and functional failures are defined for each subsystem. The function defines the performance expectation and can have many elements. Functional failures are descriptions of the various ways in which a system or subsystem can fail to meet the functional requirements.
Components of the subsystems will be defined later. Each component (equipment) in these zones is subjected to certain maintenance procedures. Generally, preventive maintenance is preferred. Table-3 and Table-4 illustrate the periodic maintenance program of the transformers and SF6 circuit breakers, respectively.
TABLE I.
Period 6 months 12 months X X X X X X X X
TOTAL 46283.3
¾
Phase-ground faults,
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Phase-phase faults,
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Phase-phase-ground faults,
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Three phase symmetrical faults and
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Open circuit faults.
There are too many component failure modes which can be thought as the reasons of the functional failures. However, they need to be aggregated for the sake of modeling simplicity at this first stage of RCM application. Here, component failure modes are classified as: ¾
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Electrical failures: overcurrent, low frequency, relay coordination failures, substation or station oriented failures.
¾
¾
Mechanical failures: break of springs, joint and connector failures, jumper failures, insulator failures, protection line failures, fitting problems, tower problems, terminal equipment ( relay, circuit breaker, disconnector, measurement transformer etc) failures,
Phase-phase to ground failure 3- phase failure
Loss of load
TABLE VII. SF6 CIRCUIT BREAKER RCM INFORMATION FORM System: SF6 Circuit Breaker Subsystem: SF6, setting system of closure spring, open-close system, electrical hardware Function Functional Failure Consequence of Failure Mode (FM) (F) (FF) the failure (FE) a. Electrical motor Mechanism cannot be Taken to b. Fuse set automatically maintenance c. Cabling Circuit breaker cannot a. Closure coil failure Taken to close maintenance b. SF6 pressure is low Opena. Antipumping relay Taken to close CB is opening consecutively failure maintenance
After having defined the functional failures and component failure modes, information form for each subsystem is generated. A. Transformer Subsystem Power transformer is the most expensive component of the transmission system. Components comprising transformer subsystem are transformer windings, bushing, transformer oil, oil tank and cooling system. Table 5 summarizes the information form created for transformer subsystem. B. Transmissioın line Subsystem Transmission line is the longest part of the transmission system. Components comprising transmission line subsystem are transmission line, transmission tower, insulators, fittings etc. Table 6 summarizes the information form regarding the transmission line subsystem.
CB does not accept manual or automatic (remote) commands.
III.
a. CB is not completely closed b. Opening coil failure
Taken to maintenance
POWER TRANSMISSION SYSTEM DECISION MAKING
Following the preparation of information forms for the subsystems, decision tree is constructed with respect to the data of those forms. Maintenance procedure for each failure is determined with respect to the failures and their consequences given in the information forms and with respect to the decision tree given in Figure 1. NASA example is taken as a reference while constructing the decision tree. [8] At each state, each probable failure mode is checked if it has a negative impact upon system security and safety. Those sequential YES/NO chain will later result in the best maintenance procedure for the failure event. Final maintenance options considered in this study are as follows.
C. SF6 Circuit Breaker Subsystem Components comprising SF6 Circuit Breaker subsystem are SF6, setting system of closure spring, open-close mechanism, electrical hardware etc. Table 7 summarizes the information form regarding SF6 Circuit Breaker subsystem. TABLE V. TRANSFORMER RCM INFORMATION FORM
Power Transformer
Loss of load
*Failures due to insulation degradation and wind effect.
Environmental failures: adverse weather conditions and lightning
System: Transformer Subsystem: windings, bushing, oil tank, cooling system Function Functional Failure Mode (FM) (F) Failure (FF) a. Lightning surge Phase to ground b. Switching surge failure c. Bushing failure d. Oil-oriented failure Phase to phase a. Oil-oriented failure failure b. Winding insulation problem a. Load increase Overloading b. Ambient temperature
a. Electrical* b. Fitting c. Adverse weather a. Tower collapse b. Adverse weather
Consequence of the failure (FE)
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P1: Appropriate parameters and procedure should be identified for Predictive Maintenance.
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P2 : Periodic Maintenance should be applied..
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P3 : There is no technical and economic benefit of predicting the chance failures before their occurrence. Therefore, corrective maintenance is the most appropriate one.
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P4 : A redundant system should be installed.
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P5 : A new design is required.
Outage
Outage Outage Outage
TABLE VI. TRANSMISSION LINE RCM INFORMATION FORM System: Power transmission line Subsystem: Transmission line, tower, insulator, fittings etc Function Functional Consequence of the Failure Mode (FM) (F) Failure (FF) failure (FE) a. Lightning surge b. Conductor break Phase to c. Switching surge Loss of load ground d. Fitting failure e. Insulator f. Adverse weather a. Conductor break Phase to Loss of load b. Immigrant birds phase failure c. Adverse weather Transmission Line
Application of the decision tree to the faults of subsystems is performed. The results are illustrated at tables 8-10.
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TABLE VIII. RCM DECISION TABLE FOR TRANSFORMER SUBSYSTEM
WILL FAILURE HAVE A DIRECT AND ADVERSE EFFECT ON SAFETY
System: Transformer Subsystem: windings, bushing, oil tank, cooling system Available Evaluation Maintenance Information Program F FF FM H E1 KB E2 PB YS A A A A A A A A
Y Y Y Y
N
N
CAN THE FAILURE BE IGNORED? (İ)
P3 P3 P2 P1 P1 P1 P5 P4
N N
N N Y
N N N Y Y Y
N N N N N N Y N
Y N Y Y Y Y Y Y
a b c d a b a b
1 1 1 1 2 2 3 3
a b c d e f a b c a b c a b
Y Y Y Y Y Y Y Y Y Y Y Y Y Y
N N N N N N N N N N N N N N
N N N N Y N N N N N N N N N
N N N Y
N N N
N N N N N Y N N N
N N N N N
Y
N N N
Y
N IS THERE A PAREMETER FOR
REDESIGN (P5)
PREDICTIVE MAINTENANCE OPTION?
Y
Y
System: Power transmission line Subsystem: Transmission line, tower, insulator, fittings etc Available Maintenan Evaluation Information ce Program F FF FM H E1 KB E2 PB YS 1 1 1 1 1 1 2 2 2 3 3 3 4 4
CAN REDISGN SOLVE THE PROBLEM COST EFFECTIVELY(E1)
N
TABLE IX. RCM DECISION TABLE FOR TRANSMISSION LINE SUBSYSTEM
A A A A A A A A A A A A A A
Y
N
N
ARE PREDICTIVE MAINTENANCE PROCEDURES ECONOMIC? (E2)
N
P3 P3 P3 P2 P1 P3 P3 P3 P3 P3 P2 P3 P3 P3
Y IS THERE A PERIODIC MAINTENANCE OPTION PRIVIDING A DECREASE IN FUNCTIONAL FAILURES? (PerM)
Y
N IS REDUNDANT UNIT REQUIRED AND ECONOMIC? (RS)
TABLE X. RCM DECISION TABLE FOR SF6 CIRCUIT BREAKER SUBSYSTEM
NO MAINTENANCE (P3)
ARRANGE PERIODIC MAINTENANCE PROCEDURE (P2)
Y
N
System: SF6 Circuit Breaker Subsystem: SF6, setting system of closure spring, open-close system, electrical hardware Available Evaluation Maintenance Information Program E1 F FF FM H KB E2 PB YS İ P2 Y N N Y a 1 A P3 N N N N Y b 1 A P3 N N N N Y c 1 A P3 N N N N Y a 2 A P1 Y Y N Y b 2 A P3 N N N N Y a 3 A P3 N N N N Y a 4 A P3 N N N N Y b 4 A
ARRANGE PREDICTIVE MAINTENANCE PROCEDURE (P1)
INSTALL REDUNDANT UNIT (P4)
Figure 1. Decision Tree Diagram [8]
system components are designed with the same principle it is not adequate to prefer a different insulation level. On the other hand, it is impossible to avoid from this kind of surges. Therefore, the result seems to be meaningful. One failure is found to be minimized by applying periodic maintenance procedure. It is phase to ground failure resulting from bushing failures. Periodic maintenance program for the bushings seems to minimize these failures. Period of the maintenance is not the subject of this study.
Eight failures are defined for transformer sub-systems. According to the results of decision tree, two of those failures are found to deal (repair) after the occurrence of the failures (corrective maintenance). These are phase to ground failures due to lightning and switching surges. Actually, transmission system is designed according to a certain insulation level required for proper insulation coordination. Since all the
Three of the failures are found to be minimized by applying predictive maintenance procedures. These are the failures regarding either insulator oil or winding insulation. Both of these failures are incipient failures that can be understood before their occurrences. Periodic transformer oil analysis (dissolved gas analysis) and winding temperature and winding insulation observations can be thought as the tools of the 146
system operation are generally allowed to happen without any pre-maintenance cares. While the other failures held differently by applying the appropriate maintenance procedures before their occurrences.
predictive maintenance procedures. Period of dissolved gas analysis is not the subject of this study. One failure is found to be non-sensitive to maintenance methods and it requires a new design for the component. Finally, one failure is found to be minimized by installing a redundant component.
In our application, transmission system is first classified into three major subsystems according to failure data collection scheme of the Turkish power transmission company. These are Transformer sub-system, transmission line sub-system and the remaining switching/control/protection subsystem.
Overloadings due to the load increase are an important problem in our electric power system. This kind of failures can be minimized by increasing the system rating either by increasing the rating of the transformer or installing a redundant transformer.
Components, failures, failure sources and their consequences are first defined separately for each sub-system. This information is later used for obtaining the RCM decision form and the most appropriate maintenance procedure is determined for each individual failures.
Finally failures resulting from ambient temperature are a matter of new design of the transformer. This new design will be able to handle high ambient temperatures.
It is obvious that the resulting maintenance procedure determined from this RCM analysis depends on the system data and on the models held for the sub-systems and failures. This initial and rough analysis have shown that the failures resulting from environmental conditions, atmospheric conditions and unexpected phenomena can’t economically minimized by periodic and predictive maintenance procedures. The best method seems to be the corrective maintenance.
Fourteen failures are defined for the transmission subsystem. There is no technical and economic benefit of predicting most of these chance failures before their occurrence. Therefore, corrective maintenance is appropriate for them and the principle is “repair when failed”. But, phaseground and phase-phase-ground failures due to fittings seem to be minimized by periodic maintenance of the fittings. On the other hand, phase-ground faults resulting from insulator failures can be minimized by predictive maintenance procedure. Leakage current can be measured and monitored as a parameter.
ACKNOWLEDGMENT The authors would like to thank to Turkish National Power Transmission Company for providing the data and information of the system.
Eight failures are defined for SF6 circuit breaker subsystem. Electric motor failures resulting a failure in automatic setting system can be held by periodic maintenance procedure. Closure problems resulting from low SF6 pressure can be minimized by monitoring the gas pressure. Therefore, predictive maintenance is appropriate for it. All the remaining failures can be held by corrective maintenance procedure.
REFERENCES [1] [2] [3]
IV RESULTS AND DISCUSSION This study has presented an RCM application in Turkish National Power Transmission System. Transmission system is first divided into subsystems and several definitions have make on those parts. All the classifications, failures and failure classifications are made according to the information from the utility staff.
[4]
[5]
This is a first attempt for such an RCM application and it is obvious that it can be improved in the future by a detailed classification of the components and the failures and by the help of more detailed data information.
[6]
The aim of RCM is to improve the reliability of the system by preventing and/or minimizing the failures with the help of applying appropriate maintenance procedure. From this point of view, component failures are held together with their impact on the system. Failures that are not of first importance for
[8]
[7]
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Moubray, J., 1997. Reliability Centered Maintenance, Elsevier Butterworth-Heinemann Lineacre House, Jordan Hill, Oxford. Dhillon, B.S., 2002. Engineering Maintenance, A Modern Approach, CRC Press, LLC. Iony P. Siqueira, Optimum Reliability-Centered Maintenance Task Frequencies for Power System Equipments, 8’ lntemational Conference on Probabilistic Methods Applied to Power Systems, Iowa Slate University, Ames, Iowa, September 12-16,2004 Beehler, M.E., 1997. Reliability Centered Maintenance for Transmission Systems, IEEE Transaction on Power Delivery, Vol. 12, No.2, 10231028. 1997 Morais, D.R., Jacqueline, G.R., Coser, C. and Hans, H,Z. 2006. Reliability Centered Maintenance for Capacitor Voltage Transformers, 9th International Conference on Probobalistic Methods Applied to Power Systems, KTH, Stocholm, Sweden, 11-15 June, p.1-6. M. E. Beehler, Reliability Centered Maintenance for Transmission Systems, IEEE Transactions on Power Delivery, Vol. 12, No. 2, April 1997. www.euas.gov.tr, WEB site of Turkish National Power Generation Company NASA, 2002. Reliability Centered Maintenance Guide For Facilities and and Collateral Equipment, U.S.Collateral Equipment, U.S.
