Impact on Engineering and Lifetime Management of Outdoor HV GIS
GIS has been used as an effective solution for the design and operation of substations since the 1960s due to its excellent features such as compactness, encapsulated components, resistance to environmental pollution and increased personnel safety due to minimal exposed high voltage components. The majority of recently constructed GIS installations are indoor, particularly in Europe and North America, but GIS applications using an outdoor design are numerous throughout the world, particularly in Asia and the Pacific Rim.
Members
Convenor
(JP)
T. SAIDA
Secretary
(GB)
N. UPPAL
G. BECKER (US), H. KÖRNER (DE), H. MISHRA (IN), J. BESTEIRO (ES), J. KALLWEIT (DE), K. ITO (JP), K. NAKAMURA (JP), M. LEE (KR), M. NAEF (CH), S. ANNADURAI (IN), S. MICHAUD (FR), T. ZIESEMER (DE)
Introduction
Extreme environmental conditions related to the location of the outdoor GIS and its exposure to constant moisture, acid rain, snow, ice, ultraviolet radiation, salt contamination, pollution, etc. contribute to its corrosion and accelerated deterioration as compared to an indoor GIS. These types of events and environmental conditions have a more pronounced effect on outdoor GIS as compared to indoor GIS. Robust engineering and design processes coupled with an appropriate maintenance strategy are the key pillars to reliable long-term operation of outdoor GIS.
One of the purposes of this Technical Brochure is to define engineering requirements and strategies for maintenance of outdoor GIS. This brochure also describes how the health of the GIS should be monitored such that the right capital and operational investment decisions can be made, at the appropriate times, to sustain the optimal performance and operational capability of the GIS.
Scope of work
This Technical Brochure identifies that there are specific design and maintenance related requirements that are unique to high voltage outdoor GIS and includes considerations for gas insulated dead tank circuit breakers or Mixed Technology Switchgear (MTS) installed in AIS substations. The impact that outdoor application of GIS has on the design of the switchgear, the high voltage interfaces and connections, the layout of the switchgear, the overall substation design and specific civil engineering issues are addressed. The impact on the long-term reliability of the GIS because of its location outdoors is explored. Specific operational impacts and other degradation impacts due to external environmental conditions are addressed (Refer Figure 1 and Table 1).
Figure 1 - Example of 300kV GIS installed in snowy areas
Table 1 - Environmental factors to be considered on design aspects
This Technical Brochure also investigates the required operation and maintenance strategies necessary to effectively ensure the reliable service life of the outdoor GIS. Economic comparisons related to the operational and maintenance strategies for outdoor GIS versus indoor GIS are explored.
This Technical Brochure provides recommendations to manufacturers and users taking into consideration the engineering, design, procurement, fabrication, civil/structural works, construction, erection & commissioning, testing, and maintenance, of outdoor GIS and MTS with gas insulated buses, local control cabinets and all accessories. These recommendations facilitate both manufacturers and users to make appropriate capital and operational investment decisions on lifetime management of outdoor GIS.
Standards, Guidelines and relevant technical documents
Chapter 2 highlights IEC international standards and national standards worldwide. It described the results of a survey on what technical requirement differences there are in terms of standards between indoor GIS and outdoor GIS. Chapter 2 summarizes the essential requirements for an outdoor switchgear (GIS and MTS) application based on national and international standards.
Market requirements for outdoor GIS
Chapter 3 describes the results of a survey of market requirements for outdoor GIS in terms of business drivers, technology drivers, environmental drivers and local market requirements. The main market requirements are similar for indoor and outdoor GIS including business, technology and environmental drivers. Local market requirements are very different, and the Working Group analyzed deeply those reasons by surveys and expert interviews.
Impact on Outdoor GIS design Including HV connection, layout, foundations and overall substation design
Chapter 4 describes the various environmental factors that have a significant impact on the performance of outdoor GIS and gives many examples of their adverse effects and relevant design countermeasures. As outdoor environmental conditions are more severe than indoor conditions, users are encouraged to consider enhancing the specifications of their outdoor GIS to avoid problems. Chapter 4 also helps manufacturers to optimize the design of outdoor GIS, to ensure the same long-term reliability as indoor GIS. Experience in several countries where outdoor GISs are predominantly used has demonstrated that proper specification and design can ensure the long-term operation of outdoor GIS.
Impact on operations and maintenance policy to ensure the outdoor GIS performance
Chapter 5 describes the implications for operations and maintenance policies to ensure the outdoor resilience of GIS. Chapter 5 also summarizes what the impact on operation and maintenance policy is to ensure the outdoor performance of GIS and MTS devices. The identification and development of strategic goals related to GIS equipment by GIS users is essential in highlighting the performance targets for GIS owners. It is important to provide focus on the aspect of SF6 gas leakage management. Chapter 5 shows different repair scenarios and best practices. The aspects of wisely planning operation & maintenance policies and determining the right corrective maintenance measures to improve the reliability of the equipment is highlighted.
Impact on Long-term reliability - Lifetime Management
Chapter 6 describes outdoor GIS management from the long-term reliability standpoint. It is important to perform thorough and comprehensive assessments on the GIS at regular intervals throughout the life cycle of the equipment. This determination is highly dependent on many factors some including severity of the outdoor environment, maintenance proficiency, exposure to severe temperature changes, exposure to pollutants or corrosive air, physical security requirements for the facility and other factors. Chapter 6 includes a lifetime management strategy flowchart to define the condition of outdoor GIS by performing cost evaluation, product capability assessment and developing lifetime extension strategy (Refer Figure 2). Also developed in chapter 6, is a Plan-Do-Check-Act cycle incorporating analysis of operational data which, leads to continuous improvement of not only local operations and maintenance strategy, but also National & International specifications and standards.
Figure 2 - Life extension / replacement decision making process
Economic Evaluation of outdoor versus Indoor GIS
Chapter 7 describes the economic evaluation difference between outdoor and indoor GIS based on their life cycle cost. In order to maintain high levels of power quality and reliability, appropriate outdoor GIS performance and maintenance activities are critical and there is cost involved in each stage of product life cycle. In general, the cost components for indoor or outdoor GIS in each life-cycle phase such as acquisition, ownership and retirement are similar. When designing an outdoor GIS or indoor GIS, the basic elements of the GIS itself do not change significantly, and in many cases, additional measures are taken to make the GIS usable outdoors as an option. These additional costs are the difference between the acquisition cost of an outdoor GIS and an indoor GIS due to other conditions such as geography, raw material availability, utility specification and manpower cost etc. GIS operating in harsh environmental conditions may cause major or minor failures more frequently, which may result in greater expenses for repair unless appropriate measures are taken in the design as the outdoor GIS. In addition, there is likely to be a significant difference in repair costs depending on the maintenance strategy. The cost of retirement of a GIS substation is likely to be tied to the initial planning and construction costs. The cost of usage of SF6 also influences the overall cost of the ownership and indirectly hints towards the retirement of the GIS substation.
Conclusion
This Technical Brochure reflects the main environmental parameters, which need to be considered and is therefore essential for the engineering and design of the equipment suitable for a typical outdoor substation. Regarding outdoor suitability of the switchgear (GIS and MTS), a clear specification that includes the description of the environment is an important basis for the planning and design of the substation and its switchgear.
For many technical challenges in the future, outdoor GIS represents a solution. It enables both the expansion and the new construction of switchgear in limited spatial conditions. In a world characterized by urbanization, one can expect that the importance of outdoor GIS will increase in the future. The local market conditions, as well as the conducted survey, show that there is a need for clarification among potential customers regarding the suitability of outdoor GIS in special environmental conditions. The expectations on the reliability and availability of the equipment are the main decision criteria.
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