Ageing switchgear: retrofit, refurbish or replace?

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Asset management of ageing switchgear equipment continues to be a thorny issue for both utility companies and industry. For utilities, with Ofgem’s updated ‘RIIO-ED1’ price control regime due in 2015, transmission and distribution network operators are renewing their focus on this question. Siemens’ Russ Elliott, product manager, and Iain Monk, head of sales, revisit the different options available to users seeking to extend the operational life of their equipment

 

Optimising the life of ageing switchgear is not a new subject, but one that continues to be a major issue for electricity suppliers and industry alike. Both have large installed bases of high voltage (HV) and medium voltage (MV) switchgear; much of it installed between the late 1950s and early 1970s, which must somehow be brought into the 21st century to ensure optimum network performance and longevity. In Siemens, we estimate that there is still a population of c.250,000 Reyrolle – now Siemens – circuit breakers in service worldwide that could be anything up to 50+ years old.

However, economic uncertainties and capital expenditure restrictions have made users increasingly cautious about automatically opting for replacement. For DNOs especially, the new ED1 regulatory period will lead to increased focus on this issue.
RIIO and cost reduction

Ofgem price controls apply to all Britain’s gas and electricity network operators. RIIO (Revenue = Incentives + Innovation + Outputs) encourages investment to ensure continued safe, reliable services; innovation to reduce network costs; and work to deliver a low carbon economy.

From 2015 to 2023, a new performance-based Electricity Distribution model, RIIO-ED1, will apply. In Ofgem’s words, this model will “… drive real benefits for consumers; providing network companies with strong incentives to step up and meet the challenges of delivering a low carbon, sustainable energy sector at a lower cost than would have been the case under our previous approach.” Note: ‘Supplementary Annex to RIIO-ED1 Overview Paper’ – Ofgem, March 2013

With such constraints, more users are seeking to extend the life of their switchgear equipment. The challenge for suppliers is to offer reliable, sustainable life-extension programmes to keep it safely in operation – alongside affordable, market-leading replacement options where that is the right decision. Essentially, users have three choices:

•    overhaul and refurbish existing equipment;
•    retrofit and upgrade the equipment;
•    replace with new equipment.

We know that this decision is influenced strongly by safety, reliability, commercial and environmental considerations. The commercial considerations are straightforward: not just cost, but the additional timescales involved in a decision to replace rather than repair or refurbish.

From a reliability perspective, the performance of decades-old equipment may fall well short of present-day requirements, especially on older developing or expanding networks, or where additional generation has been installed. This is particularly relevant where significant quantities of renewable, distributed generation are now being connected to the networks.

Health and safety is particularly important when considering switchgear that may have suffered from poor maintenance or deteriorated insulation and may be in a dangerous condition – or which depends upon manual operation, especially when reliant on the speed and actions of the operator. Other considerations include:

•    system fault levels that now exceed the rating of the switchgear
•    plain break switchgear: an older type design with no arc control devices
•    oil-insulated switchgear, which has an inherent risk of fire and explosion.

Environmental considerations are varied: such as whether to extend the life of older oil-insulated switchgear with a full refurbishment, retrofit existing oil circuit breakers with a modern vacuum alternative - or whether installing state-of-the-art gas-insulated replacements makes more sense. Continued use of older equipment prevents the need for the disposal of scrap, which could be contaminated; whereas removal of oil from the substation could prevent the need to install costly fire suppression systems: there are pros and cons from every angle!

So, how effectively do the available options address these concerns?

Retrofit

A typical retrofit involves the replacement of old circuit breakers and switches by modern vacuum circuit breakers.

This option is particularly attractive to organisations with a concentrated age profile of installed equipment and where asset replacement budgets are limited. The elimination of the need for disruptive re-cabling is a major influencer: as is cost, with no requirement for civils, transformer or cabling works.

Moreover, a retrofit of circuit boards with protection equipment can result in an operational lifetime of c.25 years, dependent on the switchgear panel’s condition – and offers minimal disruption. For a straightforward retrofit circuit breaker option, site times can be very short, perhaps even less than one day per circuit.

Often, a phased retrofit approach can avoid major system network disruption whilst delivering several key benefits:

•    significantly reduced maintenance requirements,
•    enhanced operational flexibility / automation
•    enhanced safety and environmental performance, through elimination of oil and SF6 technologies
•    potential performance and protection upgrades, as often the original switchgear panels have enhanced capabilities that can be exploited if the circuit breakers are replaced.

Retrofit works well where the condition of the existing switchgear panels is good and they can be condition-assessed to give a remaining life consistent with substation and network requirements: particularly attractive where the change from oil to vacuum greatly reduces maintenance requirements and increases the in-service time.

Refurbishment

Refurbishment restores the equipment to its original condition and performance specification. It can actually enhance ratings or performance, dependent on the equipment involved.

The big advantage of this option, like retrofit, is that no building, civils or transformer equipment are required – again, with considerable cost savings. If refurbishment of circuit breakers is required, then a ‘traveller’ scheme can be operated so changeover can be achieved in as little as a half-day’s activity on site per circuit. Refurbishment of switchgear enclosures may involve longer timescales, but generally much less than an equivalent replacement project.

Siemens operates a dedicated facility for workshop refurbishment of switchgear equipment from the original Reyrolle site at Hebburn in the North East of England: continuing and extending the proud heritage of this famous brand into the 21st century. Equipped with full production assembly and test capability, it addresses all installed types from 3.3kV to 550kV, and ensures that extension switchgear equipment can interface seamlessly with existing equipment.

Retrofit solutions covering a wide range of oil, air break and SF6 technologies are also available – fully supported not only by the full production capability but, of course, the original design information, to ensure maximum performance from any retrofit project.

DNO savings – a case study
Siemens has worked with a major DNO to develop a retrofit, refurbishment and replacement programme to extend the serviceable life of its assets and develop a strategy for ED1 2015-2023. Successful trial site piloting achieved very significant savings – in fact, as much as three quarters of the outlay that would have been required for a new, 26 panel 11kV substation (including buildings, cable, civils and switchgear).

A critical solution element was the C-Gear retrofit, replacing outdated oil circuit breaker units with a modern vacuum circuit breaker. This has been shown to expand the life of existing switchgear up to 25 years: having been type-tested at independently-accredited laboratories in accordance with IEC 62271-200 and other relevant standards. The retrofit solution was developed using all of the application engineering knowledge acquired since the first installation of Reyrolle C-Gear switchgear, back in 1906.

Replacement

After consideration of existing equipment condition, number of switching cycles, performance history, maintenance regime and latest network requirements, the decision to replace a switchboard may be the only sensible option – and in some circumstances, may lead to an upgrade or even replacement of a complete substation.

The cost of a new substation can vary depending on the level of ground works, civil works and equipment scope: involving potentially new transformers, cables, switchgear and protection & control equipment. A traditional civil build will typically cost 250 to 300% more than replacement of an 11KV primary switchboard alone – and extend the project duration to 12 months versus 6 months for replacement. However, alternative building techniques are available which allow both switchboard and buildings to be replaced with the latest technology; ensuring that the latest standards in operator safety are maintained whilst reducing both project duration and site activity.

Siemens not only provides a combination of the latest technology with competitive pricing, but innovative financing options, too. We can help procurement and finance directors examine all relevant considerations and prepare a sound business case – often revealing a lower total cost of ownership than may be anticipated.

The current extensive capital investment programmes being undertaken by UK utilities are generating renewed examination of the retrofit, refurbishment and replacement options, with the result that many different projects are now being undertaken by Siemens. Although each project requires careful evaluation, the choice is there: across all voltage ranges – with a solution being available for all circumstances.

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