Residual life aspects on GIS with the focus on SF 6

Residual life aspects on GIS with the focus on SF 6 Speaker: Karsten Pohlink 25. March 2015

The presentation refers to CIGRÉ WORKING GROUP B3.17 RESIDUAL LIFE CONCEPTS APPLIED TO HV GIS CIGRE Technical Brochure 499 (06/2012) Members: K Pohlink / Convenor (CH), C Jones (UK), P Coventry (UK), W Degen (DE), E Duggan (IE), P Glaubitz (DE), P Fletcher (UK), M Hyvärinen (FI) Z Lefter (HU), A Mjelve (NO), M Reuter (DE), B Skyberg (NO), K Uehara (JP), T Yokota (JP), Corresponding Member: D Kopejtkova (CZ) 2

Overview The TB 499 & Tutorial includes the following chapters Introduction & Scope Experience & Reliability of GIS Equipment Information & Assessment Maintenance Strategies Life Limiting Factors of GIS & Condition Assessment Impact of System Changes Support of Old GIS Options for Life Extension Evaluation Process and Health Indices Disposal & End of Life Procedures Conclusions & Discussions Case Studies All chapters include subjects related to SF 6 3

Introduction HV GIS (High Voltage Gas Insulated Switchgear) has been in service for approximately 45 years Experience has shown that GIS is generally a very reliable technology - particularly when used indoor Number of installations is continuously increasing Task: What is the service life expectation of the long time installed GIS? by: Identification and discussion of the factors which determine the expected residual life of HV GIS Guidance on evaluating the expected residual life Options for extending the residual lifetime End-of-life procedure for HV GIS including SF 6 gas Examples of residual life assessments and decisions 4

GIS Age Profile Age profile of the Worldwide GIS installed base (2010) 5

Experience of GIS Lifetime of early GIS is more than the anticipated 25-30 years - today s expectation: >50 years No generic life limiting process have been reported so far Substation build in 1973, some circuit breakers replaced around year 2000 6

Experience of GIS However some issues of ageing and deterioration have occurred in the following areas: Gas leakages (mainly for outdoor installations, flange corrosion) Specific material/design issues (graphite type bursting disks, seals) Corrosion Mechanical wear Electrical wear Issues can be solved in most cases by enhanced maintenance and refurbishment Use of a supplementary seal around the flange 7

Experience of GIS GIS 1968 8

Experience of GIS Layout of GIS bays Single/Double busbar single phase encapsulated from 1982 14

Experience of GIS Layout of Three phase enclosed GIS bays from 1984 15

GIS Reliability Survey Data from 3rd survey 2004-2007 TB513 (2012) 16

GIS Reliability Survey The general trend is towards improving reliability of newer GIS. This could be explained by an age related deterioration of older GIS; however it is our view that it is a consequence of the inherent lower reliability of early GIS designs. This view is supported by the higher failure rates reported in the first and second surveys [first survey 1991; second survey in 1996] Following aspects should be taken into consideration: Information to evaluate GIS Maintenance Strategies Life Limiting Factors & Condition Assessment 17

Evaluation process for residual life options 18

Information to evaluate GIS Name plate information [equipment] Descriptions and reports of any data available regarding operational history: number of operations, abnormal operational conditions, details of failures, inspections, maintenance, extensions, modifications, overhauls and diagnostic tests of a specific GIS [user] Feedback on service experience of equipment type [original equipment manufacturer OEM] Information on availability of spare parts and technicians [OEM] 19

Equipment information & status Evolution of GIS technology 20

History of GIS Standards Year History 1965 No standards available for GIS and designs relied heavily on equipment standards 1975 IEC 517 GIS 1 st edition 1977 Amendment No. 1, partial discharge (PD) included 1982 Amendment No. 2, focus on enclosures 1983 Amendment No. 3, internal arc testing 1986 IEC 517 GIS 2 nd edition, integration of amendments 1990 IEC 517 GIS 3 rd edition, technical update and reference to other relevant IEC standards, e.g. IEC 60694 Common specifications for high-voltage switchgear and control gear 2003 IEC 62271-203 1 st edition, reduction of gas leakage from 1 to 0.5% per annum, additional site test requirements 2011 IEC 62271-203 2 nd edition, addition of service continuity considerations 21

Maintenance Strategies for GIS Corrective maintenance - Run to failure Corrective maintenance is defined as the maintenance carried out after fault recognition and intended to put an item into a state in which it can perform a required function It is not recommended to use this maintenance strategy for GIS because it can lead to severe outages which will be unacceptable in transmission systems 22

Maintenance Strategies for GIS Preventive maintenance: In contrast to corrective maintenance, preventive maintenance aims to avoid equipment failures by taking appropriate action. Defined as maintenance carried out at predetermined intervals [time based] or according to prescribed criteria [condition based &/or reliability centered] and intended to reduce the probability of failure or the degradation of the functioning of an item This is the recommended maintenance strategy for all installed GIS and generally applied 23

Support of long time installed GIS The long service life of GIS leads to the following challenges: Knowledge and expertise Spare parts (availability, holding policy, secondary equipment) Maintenance and repair Extension Need for consultancy services 24

Support of long time installed GIS Further Examples: 25

Support of long time installed GIS Life part of substation during maintenance of single bays 26

Support of long time installed GIS Refurbishment of GIS build in 1975 27

Support of long time installed GIS 28

Life Limiting Factors & Condition Assessment Ageing and deterioration mechanisms on the following subjects are discussed in the technical brochure and the tutorial: Circuit breakers, Load break switches High-speed earthing switches Disconnectors and (maintenance) earthing switches Insulation including SF 6 Enclosures Auxiliary equipment and accessories Process applied: Life limiting factors (description, discussion, evolution) Diagnostic techniques (how to detect and assess) 30

Life Limiting Factors & Condition Assessment Mechanical lifetime for circuit breakers is defined by the permitted number of off-load switching operations. New IEC-standards define two classes for mechanical endurance: class M1 (2 000 operations) and class M2 (10 000 operations), but earlier requirements were significantly lower (1 000 operations). Diagnostic techniques: Circuit-breakers I mechanical wear Measurement of charging time, contact timing, static contact resistance, travel records, trip coil current, vibration analysis The number of operations and actual endurance class can give an initial idea of possible mechanical wear. 31

Life Limiting Factors & Condition Assessment Circuit-breakers II mechanical wear Example: travel records, normal travel curves (broken lines) and schematic examples of abnormal contact travel recordings (solid lines) from an open operation a) Delay in release mechanism, e.g. due to poorly lubricated release latches b) Low contact speed, e.g. due to reduced energy in operating mechanism c) Poor damping, e.g. due to defective dash pot d) Too low insulation distance in open position, e.g. due to incorrect assembly 32

Life Limiting Factors & Condition Assessment Circuit-breakers III electrical wear Electrical wear in contact system: Contact erosion and nozzle ablation caused by interruption of fault currents Limit of electrical wear is seldom reached Contact wear can be detected by: Visual inspection (requires opening of the GIS) Slow motion resistance measurements as shown to the right Contact resistance as a function of contact travel 33

Life Limiting Factors & Condition Assessment Circuit-breakers IV grading capacitors Grading capacitors in multi-break circuit breakers have shown various mechanical and electrical problems, some of them can lead to failures such as: Dielectric breakdown (breaking small inductive currents) Partial discharge caused by bad connections (metal band) Leaks (oil out or SF 6 into grading capacitor) Diagnosis by: Visual inspection Partial discharge measurements 34

Life Limiting Factors & Condition Assessment Insulation I: SF 6 -gas quality Life limiting factors: no ageing of the gas itself Decomposition products present in the gas indicates defects like overheated contacts or partial discharges Decomposition of the gas starts at temperatures >400-500C (>200C if Cu is present) Decomposition products can be detected by gas testing: on site or in laboratory by gas measuring devices 35

Life Limiting Factors & Condition Assessment Insulation II: SF 6 -gas quality Humidity in the gas has a limited influence on the insulation property of the gas itself, but may condense on surfaces of insulation parts and may lead to flashover Humidity contributes to the formation of corrosive decomposition products Humidity can be detected by dew-point measurements Adsorbers in the gas compartments can adsorb decomposition products and humidity SF 6 collecting device in service 36

Decomposition of SF6 and Subsequent Reactions (WG B3.25 TB 567) 37

Decomposition of SF6 and Subsequent Reactions Discharge channel Fragmented SF 6 molecules will react with materials in the contacts to produce metal fluorides and CF 4 Will react with contaminants such as H 2 O and O 2 to produce decomposition products containing oxygen such as SO 2 F 2 Surface reactions SF 4 with H 2 O to produce SOF 2 and HF HF with metal oxides to produce metal fluorides 38

Decomposition of SF6 and Subsequent Reactions Gaseous decomposition SOF 2 and SO 2 are the most abundant SOF 2 produced by the reaction of SF 4 and H 2 O SO 2 produced by the reaction of SOF 2 and H 2 O Solid decomposition products are AlF 3, CuF 2 and WF 6 39

Decomposition of SF6 General Conclusion: very complex process which is influenced by The type of discharge The energy involved The type of vessel The presence of contaminants The contact materials 40

Life Limiting Factors & Condition Assessment Insulation III: Particles Particles in the gas may reduce the insulating performance and cause flashovers Particles can be generated from moving parts like conductor sliding contacts and contacts in switching devices. Particles can be detected by: UHF and acoustic measurements 41

Life Limiting Factors & Condition Assessment Insulation IV: Particles Example UHF measurement Example acoustic measurement 42

Life Limiting Factors & Condition Assessment Insulation V: SF 6 gas leakage SF 6 gas leakage affects the gas density and also environmental aspects are to be considered Leakage rate in new IEC-standards: max 0,5 % per year from any single compartment Leakage origin and causes: seals, pipework, flange corrosion. Old GIS with controlled pressure system should be replaced by closed pressure systems 43

Life Limiting Factors & Condition Assessment Insulation VI: SF 6 gas leakage Leakage is detected by gas density monitors (mechanical pressure gauge or electronic sensors) Location of leakage can be found by negative ion capture detectors, electron capture detectors or other methods 44

Life Limiting Factors & Condition Assessment Insulation VII: Filters Filters are applied to adsorb moisture and decomposition products Filters are for the service period until opening for maintenance. Lifetime of filters in circuit-breaker compartments will depend on the value of cumulative breaking currents Gas quality measurements may give indications of the remaining filter lifetime 45

Life Limiting Factors & Condition Assessment Corrosion of metallic housings is the main concern especially flanges can be affected due to moisture ingress Outdoor substations in aggressive atmosphere are particularly exposed Corrosion leads to SF6 leakage Enclosures I: Metallic housing Example of flange corrosion 46

Life Limiting Factors & Condition Assessment Enclosures II: SF 6 gas seals Seals are subject to aging: main factors are material, temperature, UV, exposure to oxygen and combination. Aging may lead to SF6 leakages Typically EPDM is used for gas seals. If the seal is not disturbed, it is not a life limiting factor even when aged Dynamic seals are also exposed to mechanical wear and corrosion of metallic parts may occur Seals must be replaced after opening of the gas compartment Defects can be detected/monitored by leakage detection Compression set measurement can help to asses the performance of seals 47

Life Limiting Factors & Condition Assessment Enclosures III: Pressure relief device Two types of disk material are typically used in GIS: graphite and metallic. Graphite was widely used in early designs. Life limiting factors: corrosion and fatigue which can lead to SF6 gas leakage and/or reduction of the operating pressure. Detection is possible by visual inspection, leakage monitoring or by laboratory examinations It is recommended to replace graphite disks if the GIS compartment is refurbished. 48

Life Limiting Factors & Condition Assessment Auxiliary equipment and accessories Filling interface, gas monitoring, sensors, gas piping and valves are unlikely to limit the life of GIS. SF 6 gas pipework with leakage should be removed and filling/monitoring equipment directly installed to the gas compartment 49

Life Limiting Factors & Condition Assessment Secondary Equipment The life expectation of the secondary equipment is generally significantly lower then for the primary GIS Electronic components of digital secondary technique have a life expectation of 15-25 years, while electromechanical devices may reach longer life times. A replacement of parts or the complete secondary equipment may be considered to reach the life time of the GIS installation. This can also be supported by the request for extended functionality, communication features and protection system upgrades. 50

Impact of System Changes to GIS System changes may occur due to the development of the network and can be: Additional functions required Extension/Modification of bays or devices Uprating of nominal current Increase of short circuit breaking requirements Increase of system voltage Upgrading of secondary system They often require a specific residual life assessment 52

Life extension Life extension is a change of the asset management policy for the GIS so as to achieve an increased residual life. Changes that may be considered are: Enhanced maintenance Refurbishment Retrofit 54

Evaluation of options for life extension Main factors to consider when deciding upon enhanced maintenance, refurbishment, retrofit or replacement: assessed residual life and associated risks required residual life for substation costs outage time requirements technical requirements and possibilities 55

Options for Life Extension Enhanced maintenance Is a change of the actual maintenance process by increased frequency and/or scope of the maintenance work? Can extend the life of the GIS by reducing risk? Is always part of a preventive maintenance strategy which could be supported by enhanced diagnostics or monitoring? Is seen as a relative cost effective life extension strategy but it may only delay refurbishment actions? 56

Options for Life Extension Enhanced maintenance possible applications Enhanced maintenance activities: more frequently lubrication, painting, cleaning. Enhanced diagnostics: frequently executed partial discharge measurements, SF6 gas quality check, timing measurements, infrared measurements, resistance measurements, leakage measurements. Introduction of additional online monitoring. 57

Options for Life Extension Enhanced maintenance - example Introduction of SF 6 -online monitoring system: Online monitoring was implemented (in addition to the traditional two-level pressure/density sensors) Even SF 6 leakage which develops very slowly can be detected with the onlinesystem Online monitoring of SF 6 -density was first installed during a refurbishment/retrofit project of the oldest GIS-stations. Nowadays the installation of such systems is often used for new SF 6 -installations GIS with online SF 6 monitoring 58

Options for Life Extension Refurbishment A major work to return the GIS back to (or close to) original condition with no additional functionality Typically represents an investment made only once in the lifetime (normally after mid life onwards) on a subassembly which has been identified as life limiting The subassembly is dismantled, inspected, cleaned and repaired by replacement of the wearing parts Done on site or in a workshop depending on the scope of work and the need of specific tools and test devices 59

Options for Life Extension Refurbishment possible applications Components that would normally be considered during a major refurbishment are: SF6 gas seals (static and dynamic) weatherproofing and corrosion protection mainly for outdoor GIS and GIS in harsh environments moving parts/parts subjected to electrical/mechanical wear 60

Options for Life Extension Refurbishment - example A variety of procedures have been developed to deal with SF6 gas leakages caused by flange corrosion. Two examples of applying a supplemental seal are depicted below. Major benefit: No dismantling required 61

Options for Life Extension Retrofit Specific components or major parts are replaced with new units of an enhanced functionality and/or increased specification The enhanced functionality may consider primary or control, protection and monitoring equipment Often an upgrading/uprating of the primary GIS is associated with a retrofit of the secondary system 62

Options for Life Extension Retrofit possible applications Increased specification: increase of rated short circuit current or rated current, improved tightness, reach updated IEC requirements, higher number of mechanical operations Change of circuit breaker, interrupter elements or drives to more up to date technology Enhanced monitoring, control and protection systems: remote control / unmanned substation, new protection functions, additional monitoring (may also require the installation of sensors) 63

Options for Life Extension Retrofit example 1 400 kv GIS circuit breaker drive retrofit: An unacceptable number of failures in the original hydraulic drives occurred Refurbishment or retrofit? It was considered that the fault rate would increase again in future even if all known modifications to the original drive were implemented. It was decided to replace the complete drive with current technology solution. 400 kv GIS with circuit breaker drive retrofitted 64

Options for Life Extension Adding a disconnector in busbar to improve availability of a 300 kv substation: Retrofit example 2 A sectionalising disconnector was installed in one busbar in a double busbar system. The modification has significantly increased the availability of the substation, as it is possible to split the busbar. Additional installed bus sectionaliser 65

Options for Life Extension Replacement May consider the whole GIS installation or a major part of it. Replacement is in many cases connected to an increase of functionality and enhanced specification (e.g. number of bays, Single Line Diagram, short circuit current level). Two basic options to build the new installation: On the same footprint: a stepwise approach can be used as new GIS normally require less space. Alongside the existing GIS: circuits are transferred. 67

Options for Life Extension Replacement example 1 Replacement of one of the first GIS: The substation was commissioned in 1968 and removed from service in 2002. It was considered to have reached the end of its life due to a lack of spare parts and unacceptable level of gas leakage. GIS upper floor with circuit breakers (1968) 145kV GIS lower floor with busbar and cable connections (1968) New 170kV GIS installation (2003) 68

Options for Life Extension Replacement example 2 Replacement of 400/275kV GIS Substation: For an existing 400kV single busbar GIS additional 400kV cables & future system requirements demanded a full double busbar substation and extension of the 275kV substation It was concluded that it would not be feasible to adapt or extend the existing GIS A new 16 bay 400kV GIS was build alongside the original substation and the existing circuits were reconnected to the new switchgear. The existing 400/275kV transformers were connected to the new substation by gas insulated busducts. General view of original GIS New transformer compound 69

Disposal & End of Life Procedures Recycling and disposal If end of service life of the GIS is reached, defined dismantling and disposal must be done. Before dismantling the GIS it is required to remove the SF 6 for reuse or recycling. Depending on the category of the gas: It can be reused directly (values within the limits given by IEC 60480), or In some cases the gas has to be treated, or Sent back to the manufacturer of SF 6 Dismantled GIS could be a source for spare parts or a high content can be recycled (Al, Cu, Fe) 70

Disposal & End of Life Procedures Structure of used material taken from one bay with aluminum enclosure 71

Recommendations to Original Equipment Manufacturers (OEM) Assure availability of documentation for installed equipment Provide failure history / statistics for installed equipment types (major / minor failures) Inform the user of changes in maintenance recommendations or other activities if any Assure lifetime support of installed equipment (assessment, maintenance, modifications, repair, spare parts) Provide solutions for extendibility of installed GIS 72

Recommendations to Users Consideration in the original planning phase for possible extensions, replacements and refurbishments in future Keep the documentation available about the installed equipment (technical, schematics, reports & test sheets) Collect and file documentation of equipment history including maintenance actions, operations, modifications, diagnostic results, measurements, tests carried out, minor/major failures. Inform the OEM about minor and major failures Formalize the process of updating maintenance policies and practices based on latest industry experience. Participate in future CIGRE reliability surveys 73

Outlook Today the limits of lifetime for GIS are not known 74

Conclusion The experience of the lifetime of a GIS is >45 years, therefore today s life time expectation is above 50 years Corrosion, gas leakages, specific material/design issues and in some cases mechanical and electrical wear are the main issues for deterioration Frequently inspection and subsequently maintenance actions, assessment methods, diagnostic techniques and effective quality control processes enable the expected lifetime of a GIS Life extension can often be achieved by enhanced maintenance, refurbishment or retrofit End of life: requires a complete and sustainable recovery of SF 6 replacement with a new GIS is often selected Publication: CIGRÉ TB 499 SF 6 Analysis for GIS, AIS and MTS Condition Assessment - CIGRE WG B3.25 TB 567 75