Asset management of ageing switchgear has become a big issue for both utility companies and industrial users in recent years. Chris Jones, service portfolio manager of Siemens Transmission and Distribution outlines the different options available to users to extend the operational life of their equipment
Maximising and optimising the operational life of ageing switchgear equipment is a major issue for both electricity suppliers and industry. Both have large installed bases of high and medium voltage switchgear, much of it installed between the late 1950s and early 1970s, which must be brought, in one way or another, into the 21st Century to ensure optimum network performance.
However, the requirement to enhance shareholder value and tightly control capital expenditure has led owners of ageing switchgear to investigate partnerships with equipment suppliers to utilise aftermarket capabilities and implement plant life extension programmes to keep their switchgear safely in operation.
Globally, there is a constant process underway to extend the operational life of switchgear equipment - a process that demands difficult decisions from its owners. For example, our own estimates suggest that there is a population of Reyrolle, now part of Siemens, medium voltage and high voltage products which could be anything up to 50 years old, of approximately 250,000 units still in service worldwide.
Manufacturers of switchgear have recognised the opportunities presented by this ageing installed base by offering products and services that constitute a more comprehensive customer support or ‘aftermarket' capability. This has led manufacturers to become even more closely involved with owners and operators to understand the operational difficulties surrounding ageing switchgear and to help users arrive at optimum solutions.
As a result of this increased focus on the aftermarket, users of switchgear are now faced with three distinct choices; overhaul and refurbish the equipment to keep it operational for a further period of time; retrofit and upgrade the existing equipment or, finally, replace with new equipment.
Multiple factors will influence the decision to retrofit, refurbish or replace from health and safety through to growing environmental considerations, not forgetting the commercial aspect. Equipment that is decades old may now fall short of present-day performance requirements, especially on older developing or expanding networks, or where additional generation has been installed. This is a particular feature today with the significant quantities of renewable and distributed generation being connected on distribution networks.
The health and safety related issues with elderly switchgear can be categorised as:
- Switchgear which is dependant upon manual operation, in particular that which relies on the speed and actions of the operator.
- System fault levels which now exceed the rating of the switchgear.
- Plain break switchgear, an older type design which has no arc control devices.
- Poor quality or a complete lack of maintenance that has left the switchgear in a dangerous condition.
- Insulation deterioration due to age and environmental conditions.
- Oil-insulated switchgear which has an inherent risk of fire and explosion
The Replacement Option
Replacement of a complete substation or switchboard is normally the most costly solution involving significant outages and project timescales, but generally ensures the longest residual life for the installation, should this be a significant requirement. Where the existing equipment is particularly old or troublesome then replacement could be the obvious choice, although risks due to cables being disturbed are one complication which requires careful consideration.
Cost is a significant factor with a new substation. It involves building and civil work, transformers, cables, switchgear and protection equipment and will typically be between 250-300% more expensive than a replacement with an 11kV board, but it will have a similar operational life, once installed, of at least 35-40 years. The project duration for the replacement option is often approximately six months compared to 12 months for a new substation with only two-three months required on site.
However replacement does ensure compliance with the latest standards and, of course, the opportunity to ensure enhanced performance of the equipment itself.
The Retrofit Option
A typical retrofit involves the replacement of existing old technology circuit breakers and switches by modern vacuum circuit breakers, normally without the need for an inconvenient busbar outage.
The retrofit option is particularly attractive to organisations with a concentrated age profile of installed equipment, where asset replacement budgets need to be tightly controlled. The elimination of the need for re-cabling, with the consequential disruption involved is a major factor in choosing the retrofit option. Cost is another reason for choosing the retrofit option with no requirement for civils, transformer or cabling costs.
Furthermore, a retrofit of circuit boards with protection equipment can expect an operational lifetime of approximately 30 years, dependent on the condition of the switchgear panel and offers minimal disruption with an average project duration of three-four months with five-six weeks on site. For a straightforward retrofit circuit breaker option the 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 at the same time deliver
- Low maintenance circuit breaker solution which is offered by modern vacuum circuit breakers compared to the high maintenance required on older technologies.
- Enhanced operational flexibility/automation
- Potential performance and protection upgrades. Often the original switchgear panels have enhanced capabilities compared to the original circuit breakers which can be exploited if the circuit breakers are replaced.
- Enhanced safety and environmental performance through the elimination of oil and SF6 technologies.
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 the requirements of the substation and network. Retrofit is particularly attractive on auto-reclose circuits where the change from oil to vacuum greatly reduces the maintenance requirements and increases the in-service time.
The Refurbishment Option
Refurbishment covers the restoration of the equipment to its original condition and performance specification. Some refurbishment projects may also encompass the enhancement of ratings or performance dependent on the equipment involved.
The big advantage of the refurbishment option, like retrofit, is no building and civils and transformer equipment is required which results in a considerable cost saving. If refurbishment of circuit breakers is required then a traveller scheme can be operated such that changeover can be achieved in as little as a half day activity on site per circuit.
Refurbishment of switchgear enclosures may involve longer timescales but generally much shorter than for an equivalent replacement project.
Siemens has established in the UK a dedicated facility for workshop refurbishment of switchgear equipment covering all the installed types from 3.3kV up to 550kV. The same workshop facilities are equipped with full production assembly and test capability so that extension switchgear equipment can be provided to seamlessly interface with existing equipment. Retrofit solutions covering a wide range of oil, air break and SF6 technologies are also available which are fully supported not only by the full production capability but, of course, the original design information to ensure maximum performance of any retrofit project.
The current extensive capital investment programmes being undertaken by utilities in the UK is generating renewed examination of the retrofit, refurbishment and replacement options with the result that a wide diversity of projects are now being undertaken in the UK and overseas by Siemens. Each customer circumstance requires evaluation in order for the optimum solution to be selected, but the choice is there across all voltage ranges in the UK, with a solution being available for all circumstances.
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