REFURBISHMENT OF SECONDARY SYSTEMS IN HIGH VOLTAGE SUBSTATIONS LESSONS LEARNED IN VENEZUELA

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1 21, rue d'artois, F Paris B3-110 Session 2004 CIGRÉ REFURBISHMENT OF SECONDARY SYSTEMS IN HIGH VOLTAGE SUBSTATIONS LESSONS LEARNED IN VENEZUELA by E. PADILLA * L. CEDEÑO E. PELAYO A. DICTAMEN F. ANTOIMA C.V.G. EDELCA (Venezuela) The expected life time of secondary systems based on analogue technique is around 35 years. However, some circumstances such as extensions to the high voltage switchgear and reconfiguration of the substation lay-out, offer the opportunity to actualize the secondary system, in order to improve the capability and functionality of the whole substation using up to date technology. This paper deals with the refurbishment of secondary equipment at an existing 765 kv substation located in western Venezuela, where the wall mimic was replaced by a computer based HMI (Human Machine Interface) connected through optical fibre to RTIU (Remote Terminal Intelligent Units) located in relay rooms. In this particular case, some of the equipment, including the Event Recorders and the existing Remote Terminal had problems of obsolescence (e.g. Y2K compliance) and there were also difficulties in obtaining spare parts. Introducing the new RTIU and HMI connected through optical fibre cable solved these problems in a practical way, but a lot of preparatory work was necessary in order to reduce the problems during the actual refurbishment. As well as the new technologies incorporated into both the control system and the communication equipment, the paper discusses various critical technical, human and contractual factors which arose during the execution of the project, which should be clarified at an early stage of any future project of a similar nature in order to ensure maximum effectiveness both economically and in terms of project duration. Technical factors, such as lack of components on the market to expand some of the installed equipment, job execution at site, extended engineering time and coordination work to integrate elements coming from different providers, limitations in the modification of existing boards taking into account the permissible outage time, and unexpected details of existing internal wiring that influenced the scope of supply. During the engineering stage there were additional factors related to new requirements, especially in the communication services where network components such as routers and switches were necessary to achieve the new requirements; the quantity and quality of signals to be shared between the conventional existing wiring and the new supervisory and control system that had to be defined, and problems arose due to the as built drawings not reflecting the actual situation in the substation. Human factors, such as differences in concepts between maintenance and engineering personnel regarding the elimination of the wall mimic and its replacement by the PC based HMI; the definition of the sequence of the stages required when energizing the substation with the new supervisory and * C.V.G. EDELCA, Av. La Estancia, Edf. General, Piso 3, Chuao-Caracas, Venezuela; epadilla@edelca.com.ve 1

2 control system; difference of criteria between the utilities interconnected in the substation (C.V.G. EDELCA, CADAFE and ENELBAR). Contractual factors such as the convenience or not of desegregating the contract for the new supervisory and control system from the contract for the extensions to the remainder of the substation, and the timing between the signing of the different contracts. Actually, in the existing C.V.G. EDELCA network it is possible to improve the secondary system for substations for 765 kv, 400 kv and 230 kv, as much as twenty or thirty years old, by taking advantage of new technology based on computers and replacing existing wiring and obsolete equipment. Apart from describing each of the critical factors found during the execution of the project, the paper suggests the way to reduce the possibility of them to become obstacles in the development of new refurbishing projects on the secondary systems in other substations. Keywords: Refurbishment Updating Lifetime Secondary Systems Substation. 1. YARACUY SUBSTATION Yaracuy substation, to which this paper refers, is one of the most critical and important substations on the Venezuelan 765 kv system, due to its position as the interconnection between the centre and the west of the country. It is located close to Barquisimeto, Lara State, to the west of the country. From this substation, C.V.G. EDELCA supplies energy to CADAFE and ENELBAR, public utilities which own important distribution networks. The substation was first commissioned in 1990, and comprised two incomplete 765 kv bays and a bank of 765/400 kv transformers. In the year 2000, due to the increase in power demand in the western region of the country and the need to increase the reliability of the energy supply, it was necessary to undertake an extension to the Yaracuy substation. This extension consisted in completing a ring arrangement of four circuit breakers in the 765 kv bays in order to add a new bank of 1000 MVA, 765/230 kv transformers made up of three single phase units of 333 MVA each, and a spare unit. Figure 1 and Figure 2 show the initial and final configurations of the substation. Fig.1 Single line diagram of Yaracuy substation. Initial configuration Fig.2 Single line diagram of Yaracuy substation. Final configuration. Although the secondary system of the substation had not reached the end of its useful life in accordance with the statistics and considerations indicated in reference [1], some of the components had become prematurely obsolete. This was the case with the event recorder system which did not pass the Y2K verification tests, and the system of remote terminal units (RTU) for the transmission of signals to the C.V.G. EDELCA s Main Control Centre. Thus, the extensions needed to the high voltage switchgear and transformer capacity was seen as an opportunity to update the secondary system so as to incorporate new equipment based on a new Remote Terminal Intelligent Unit (RTIU) which would perform the functions of the existing remote terminal and at the same time those of the events recorder and the transducers. 2

3 2. SCOPE OF WORK ON THE SECONDARY SYSTEM In order to obtain an optimal solution for the secondary system, and minimize the problems which could arise during the modernization process, a review of the existing secondary system was carried out during the basic engineering stage (preparation of technical specifications), from which the following was determined: 1. The Events Recorder system did not comply with Y2K requirements. 2. It would be necessary to replace the existing remote terminal, as due to obsolescence, it was difficult to obtain spare parts. 3. There were also problems in obtaining spare parts for the existing mimic control panel. 4. It had been difficult to obtain spare parts for the transducers in the control panels, due to obsolescence. 5. There was a fibre optic cable between the Control Room and the Relay Room with sufficient pairs available for the transmission of information between the two buildings where the events recorder and remote terminal are installed. 6. There was a fibre optic cable between the Relay Room in C.V.G. EDELCA s 765 kv, switchyard and the Control Room in CADAFE s 230 kv switchyard with sufficient pairs available for the exchange of information between the two companies. Once this diagnostic had been completed, it was necessary to carry out an evaluation of the technical options available for the project, taking into account C.V.G. EDELCA s experience in the installation and operation of both conventional and digital control systems [2]. After analysing the possible options, it was decided to adopt a hybrid system based on the installation of Remote Terminal Intelligent Units (RTIU) in new interface panels (TI-R) located in the Relay Room. All the information related to control, signalling, metering, auxiliary services and the transformers fire protection system of bay 4 coming from the new high voltage equipment would be cabled to these panels together with the information from the existing bays 2 and 3. From these RTIU, all the signals would be transmitted via fibre optic cable to the substation control room where the human-machine interface (HMI) would be installed for the display and control of the information. From these same RTIU, the information would also be transmitted to the C.V.G. EDELCA s Regional Control Centre. In this way, the existing wall mimic would be replaced by the new HMI and the existing remote terminal unit replaced by the RTIU. It would also be possible to eliminate the existing transducers as the new RTIU could accept the signals directly from the switchyard equipment. The control schemes prior to the development of the project and as finally installed are shown in Figures 3 and 4 respectively. Fig.3. Actual supervision scheme of Yaracuy 765 kv substation Fig.4. New control scheme. Extension to Yaracuy substation The exchange of information with C.V.G. EDELCA s customer in the 230 kv, switchyard would be made using the existing fibre optic from the new RTIU to an interconnection panel (TIEC) located in 3

4 CADAFE s control room. The same route could be used to take the control and metering signals to and from the 230 kv and 765 kv switchyards, thus reducing the need to purchase energy meters for the 230 kv, switchyard as the signals would be taken by fibre optic. The protection of the interconnection between the two switchyards would also be cabled to this panel. The schematic distribution of the signals between the two switchyards could be seen in Figure 5. Fig.5. Schematic distribution of the signals between C.V.G. EDELCA and CADAFE. In order to define the scope described, which was part of the basic engineering, it was essential to include the active participation of the operation and maintenance departments together with the engineering staff, in order to reduce deviations in the scope and execution of the project and to consolidate the bid documents. CADAFE was also included in the project at this stage. For the execution of the work, two contracts were awarded: One contract for the supply, erection and testing of the new control system (RTIU and HMI) and the other for the supply, erection and testing of the high voltage equipment together with the integration of the rest of the components which made up the extension to the substation as a whole. 3. CRITICAL ISSUES WHICH AROSE DURING THE EXECUTION OF THE PROJECT As critical issues, in this paper were considered all those technical, human, or contractual situations which gave rise to a series of clarifications and agreements both internally within C.V.G. EDELCA and externally with customers and contractors. These critical issues consisted mainly in the following: 3.1. Technical Factors Among the critical technical issues that influenced into the project, the following could be mentioned: Premises for the expansion of existing equipment In accordance with the project specifications a set of electronic cards should be added to the existing communications equipment to permit the exchange of control signals, particularly indications and metering, to and from the CADAFE 230 kv switchyard. Due to the technological advances made by the manufacturer of these electronic cards, it was necessary to use the new teleprotection panels supplied under the project for this function. It is C.V.G. EDELCA s normal practice to separate the control signals from the teleprotection signals, but in this case, in order to adapt to the available technology, it was necessary to incorporate both functions in the teleprotection panel Additional engineering to realize the interface. In the scope of the integration contract it was foreseen that all the signals coming from the high 4

5 voltage equipment would meet at a series of terminal blocks located in the interface panel TI-R, which in turn would be connected to the control system supplied under another contract. In the detailed engineering stage it was found necessary, for the correct coordination of the two contracts, that these signals be previously identified, ordered and prioritized in order to generate the data base required by the RTIU of the new control system Problems with as-built drawings. During the development of the detailed engineering it was necessary to refer to the as-built drawings of the existing installations. It was found that these did not fully reflect the on-site situation, in regard to the control signals which should be generated. Additionally, there was no drawing of integration between the signals for a conventional type control system and those required by the new control system at the level of the interconnection panel (TI-R). These problems had to be resolved during the detailed engineering phase in order to correctly define the data base to be used by the new RTIU Use of new cables in place of the existing ones Taking into consideration the location of the panels and for economic reasons, during the basic engineering stage the most appropriate option was considered to be the re-routing of the cables connected to the existing events recorder into the new TI-R panels. Nonetheless, during the detailed engineering stage this option was reconsidered, and for operational reasons, it was decided to keep this recorder in operation until the new RTIU was available. This new option required the use of new cables for the signals which were to be taken from the existing panels to the TI-R panels, which also simplified the erection and testing of the equipment Restrictions on the wiring connections in existing panels. Yaracuy substation is of vital importance for the operation and supply of the transmission system in the west of Venezuela. For this reason, the C.V.G. EDELCA s Main Control Centre management considered it inconvenient to eliminate the information being provided by the existing events recorder, thus it was necessary to have the new RTIU ready for operation prior to the disconnection of the existing recorder. The same situation arose with the cabling from the existing control and protection panels to the new TI-R panels Sequence of the work associated with the energization of the bays. During the phase prior to the erection and testing it was considered necessary to form an on-site interdisciplinary working group. This group proposed that the commissioning should be carried out in stages and that the first priority would be bay number 4 as this would provide availability for the energization of the transformer bank, which in turn would supply energy to the CADAFE 230 kv busbar. This would be followed by the energization of bay number 3 and finally of bay number 2. It should be noted that this proposal took into account the normal time taken for the different activities associated with testing high and low voltage equipment in an energized substation, and the availability of the existing panels, particularly the events recorder. Among the reasons forming the basis for the adoption of this sequential scheme for the commissioning of the substation, the priority in providing service to the client, difficulties in obtaining permits for outages, and the need for minimizing operational risks were taken into account. This also permitted the commissioning of the new RTIU for the supervision and control of bay number 4 and then, depending on the operational restrictions of the substation, the incorporation of bays number 2 and 3, thus allowing the testing of the new supervision and control system for the substation with a minimum risk Communications between the RTIU and the HMI. In order to send the signals between the RTIU and the HMI via the existing fibre optics, it was necessary to acquire and install electro-optical converters both in the RTIU and the HMI. This equipment had not been included in either the integration contract or in the control system contract, but they were easily obtained and installed and did not cause any delay in the overall programme of work. 5

6 3.2. Human Issues Among the critical human issues that influenced into the project, the following could be mentioned: Re-evaluation of the retention of the wall mimic. From the basic engineering stage it had been contemplated that the existing wall mimic (Figure 6), would be deactivated and that the control at the substation level would be performed from the new computer based master station HMI (Figure 7). Along the development of the detailed engineering, some of the maintenance personnel proposed that this concept should be reconsidered and that the existing wall mimic should be retained and operated in parallel with the new HMI, based on the idea of having a back-up for the local control of the substation. This proposal was considered during a series of meetings and additional discussions to re-evaluate the decision taken during the basic engineering. The decision to dispose of the existing wall mimic was finally ratified and the control of the substation left to the new master station shown in Figure 4. Fig.6. Wall mimic to be removed. Fig.7. New main control centre Sequence in the development of on-site work. Due to its location in the national 765 kv grid, it is a requirement that Yaracuy substation be maintained in a state of reliable commercial operation, even while extension work is under way, as an outage or fault in the service would be extremely sensitive. For this reason, in addition to the precaution of carrying out the work in stages, extreme precautions were taken to guarantee electrical service by careful planning and executing each activity. For example, the local operation of the substation from the relay room was not allowed. Under other circumstances this would have permitted the acceleration of the commissioning of the substation extension CONTRACTUAL ISSUES The basic premise adopted for the performance of the project consisted on the separation of the contracts for the substation extension and the incorporation of the new remote intelligent terminal unit RTIU. As well as these two main contracts, the new power transformers and the communications equipment also had to be acquired. The works associated with the extensions to the 230 kv switchyard which were to be undertaken by C.V.G. EDELCA s customers CADAFE and ENELBAR was also a factor to be considered. The critical issues which arose were the following: The effect of separate contracts. The number of contracts mentioned above increased the complexity of coordination of the work by C.V.G. EDELCA. This complexity of coordination had consequences in time and costs and required meetings and agreements with different working groups belonging to separate organizational units, particularly with the contract related to the creation of the data base necessary for the processing of signals coming from the switchyard. 6

7 Different time scales for the contracts. The time scale for the main integration contract was 15 months, but for the supply and erection of the new RTIU was 6 months. In addition, these two contracts were managed by different organizational units within C.V.G. EDELCA. The difference in time scales and the proper planning of the contracting both internally and with customers CADAFE and ENELBAR, reduced the impact on the time of execution of the work, even taking into account problems of technical definitions, restrictions in the availability of existing panels and the sequence of energization adopted for the commissioning. 4. ANALYSIS OF THE CRITICAL ISSUES Within the framework of the philosophy of lessons learned which is now being applied in the electrical industry, the causes which gave rise to the critical issues reported in this paper were identified, together with the effects which they had on the development of the project. The results of this analysis are shown in Table I. Table I. Summary of Causes and Effects Issue Item Attributed Cause Effect Cost Time Other Technological advances in existing equipments Need of matching both new and old technologies Lack of previous verification of existing updated drawings TECHNICAL Need of simplifying operation, erection and commissioning HUMAN Need of keeping the availability of the substation Priority in providing service to customers and testing of the new bay Minor devices not defined during engineer stage Some maintenances people not convinced about removing the old wall mimic Maximum security criteria for commissioning CONTRACTUAL Different organizational units Different magnitude of works and organizational units 4. CONCLUSIONS The main experience reported in this paper arose substantially from the decision taken by C.V.G. EDELCA to contract the work in two separate contracts, one for the supply and installation of the control system and the other one for the works associated with the high voltage switchgear extensions and the integration of the works as a whole. In general, this case shows that this method of contracting for works of modernization or refurbishment implies a greater investment of time and energy on C.V.G. EDELCA s part in the coordination of the project to avoid delays in the supply of energy to the main customer. Not withstanding although it is certain that the work was developed in a segregated manner and with a high level of technical complexity, the harmonious way in which the working team operated, achieved success in the compliance within acceptable limits of the targets for time of execution, cost and quality, as well as the performance of the work without fault and with a high level of security taking into account the operational conditions of the Yaracuy substation. This teamwork was achieved starting from the conceptual and basic engineering stages, right through the detailed engineering, construction, erection testing and commissioning stages, both within C.V.G. EDELCA and jointly with customers CADAFE and ENELBAR. 7

8 As a contribution for future projects of this nature, from the lessons learned during this project, the following are suggested: Evaluate the optimal way for contracting the integration of the new control system and the extensions to the substation. At the outset of the project, define the list of signals and the interface such that the data base for the new control system can be defined at an early stage in the most precise manner possible. During the basic engineering should be defined which existing cables should be replaced in order to reduce the need to disconnect existing panels. From the outset of the project, the sequence of work required in order to avoid outages at both high and low voltage levels, should be defined. Verify, or include in the scope of the contract, the actualization of the As-Built drawings and keep this information up to date. 5. REFERENCES [1] L. Graines, Lifetime assessment and updating of substations, [Cigré 1994, , París] [2] E. Padilla, Experience on numerical substation protection and Control System in EDELCA Network, [Cigré 2000, , París] 8