When and why should I replace my High Voltage equipment?


High Voltage electrical assets are the unsung heroes of industrial prosperity and growth. Transformers and switchgear are often kept in dark dusty substations, in basements, on site peripheries or buried amongst manufacturing product stockpiles. Frequently given less attention than the kettle plug that receives an annual PAT test, these electrical titans provide all of the power to or from a site, carrying the full burden of capacity – diligently humming away in the corner, delivering the lifeblood to all major industrial, commercial, renewable and residential facilities worldwide. How vital these assets are cannot be over emphasised – when they stop, everything stops; when they are inefficient, they are costly; and when they fail, lives can be in danger.

A replacement strategy for high voltage assets is therefore essential for the ongoing, safe and reliable operation of any major facility.

Historical Growth and Ageing Assets

During the post-war economic industrial boom period of the 1960s and 70s large volumes of High Voltage transformers and switchgear were installed throughout Britain as manufacturing soared and the demand for power followed. It is now understood that high voltage asset stock from this period has exceeded its design life cycle, and replacement should be considered in order to maintain a safe and reliable power supply.

Although switchgear and transformers can be replaced based upon an assessment of various factors that cause degradation, such as operating conditions and environment, plus the type of equipment and maintenance history, ultimately age plays a key role in the decision-making process for replacement.

Within the high voltage engineering community there is a well-regarded industry rule of thumb that switchgear and transformers have a service design life of around 40 years. However, independent service life-cycle theories have also focused on the one element that prevents the high voltage assets from faulting, internal insulation. These theories suggest that insulation performance could not be verified beyond 25 years due to time-based deterioration of the dielectric materials used, such as polymers, ceramics, resins and oil impregnated papers. Following discussions with suppliers of high voltage equipment they also concur with this theory and will not normally verify the integrity of equipment beyond 25 years.

Risk Assessment

The risks associated with high voltage oil filled switchgear and transformers can be significant. Operating high voltage equipment beyond recommended design life expectancy can result in catastrophic failure, due to internal dielectric and mechanical deterioration, with potentially fatal consequences. In extreme cases this can result in the closure of facilities by the HSE pending investigations as well as the prosecution of individuals under modern corporate manslaughter law. In order to make a risk assessment, we look at the likelihood of failure of equipment, balanced against the consequences. If we look at the consequences first, the HSE state:

“Failure of switchgear can lead to fires and where oil-filled equipment is involved the incident can be a major one. A serious incident not only poses potential fire risk and smoke risks to people in the vicinity and to the building fabric but may also affect other plant, thus escalating the primary event”.

The likelihood of an incident occurring increases based on a number of factors, age, operating environment, number of operations, defects and lack of maintenance. Although the effects of a fire can be mitigated to a certain degree, the most comprehensive risk reduction associated with oil switchgear is achieved by replacing for a non-oil equivalent device. SF6 and Vacuum variants of switchgear are widely used now as a common replacement for oil switchgear in the effort to reduce fatal accidents to zero. Most UK DNO’s (Distribution Network Operators) adopted this asset replacement strategy in the 1990’s, with the advent of low cost 11kV SF6 circuit breakers and switches.

High Voltage assets quietly deliver power to facilities on a day to day basis, keeping the lights on in schools and universities, hospitals, prisons and ports and serving as the driving force behind UK industry. In order to keep facilities operating safely and at optimum efficiency whilst also minimising unnecessary costs and the risks of failure, a High Voltage plant replacement strategy should be a fundamental consideration for any asset management team.

Reasons to replace

The following table lists the key drivers for the replacement of high voltage assets along with the benefits of replacement:

Action:Replacement Driver:Key Benefits:
Replace age expired HV equipmentAge expired assets carry the inherent risk of failure due to age related degradation. This is a normal progression for any plant item, but with High Voltage equipment catastrophic failure becomes a real possibility, and one that comes with severe consequences (sometimes fatal), business downtime plus ancillary costs for clean-up, re-enabling and generators.Inflated ongoing maintenance costs of older plant should be considered.The replacement of older transformers for modern high efficiency, low-loss units can provide asset owners with greatly reduced running costs and in some cases rapid payback periods.·        Reduce risk to personnel·        Maintain legal compliance·        Minimise Loss of Power·        Maximise plant production time·        Minimise costs associated with temporary generated power·        Ongoing maintenance cost savings·        Lower running costs·        Quick payback on investment·        Improved network resilience
Replacing non-age expired HV equipmentReplacing serviceable transformers may seem counter intuitive to most engineers. However, depending on load profiles, replacing with modern high efficiency low loss units can still prove to be a sound investment, and one that delivers a fast payback, reduced ongoing energy bills and improved carbon credentials.·        Reduced energy costs·        Improved carbon credentials
Asset UpgradesA new production line or expansion of your facility may require the replacement of an under rated transformer for something more capable for the task ahead. The replacement transformer will also have the benefit much more efficient and therefore will start delivering per unit energy cost savings from the moment it is powered up.·        Increased capacity·        Reduced per unit energy costs
Replacing redundant equipmentRationalising a high voltage network by replacing large underutilised switchboards for something modern and compact may be the right choice for your business and at the same time reduce the costly burden of maintaining redundant equipment.·        Reduced maintenance costs·        Improved network resilience

And last but by no means least the government’s Asset Investment Allowance (AIA) provides tax relief on new assets purchased for your business (up to a maximum annual allowance). This means that 100% of the cost of the investment comes out of pre-tax business profits thus providing tax relief to the value of the asset replacement, including installation costs. This is another great benefit to businesses who are looking to secure their long-term security of supplies, maximise cost saving efficiencies and reduce health and safety risks in the workplace. For 2020 (up to the 31st December) the maximum allowance has been set at £1 million – the highest figure ever set by the UK government since the scheme began in 2008!

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