There is no legal requirement to replace aged oil filled switchgear with modern vacuum types. The fact is most switchgear, of any age, if properly maintained is both safe and reliable. oil filled switchgear has been with us a long time and has proven to work well. In which case why does there remain an imperative to upgrade oil filled equipment? There are safety, reliability and cost considerations that belie the above statements, as Tony Harris of the PBSI Group explains
Safety, reliability or cost in any combination provide a real incentive to evaluate existing switchgear in any application. In spite of the fact there is no legal requirement to modernise existing aged installations, the Health and Safety Executive, the British Standards Institute and the Institution of Engineering and Technology have all published documents relating to safety. By the same token, major users of switchgear, such as the UK’s Network Distribution Operators and the power generation industry have also highlighted the need to modernise because of the mission critical nature of their applications. Finally the rising costs of maintenance and the, often, punitive penalties for system failure have added a significant motivation for renewal.
Dealing with safety issues first and foremost, it must be reiterated that dangerous failures of switchgear are rare. Unfortunately, rather like other rare failures, such as aircraft malfunctions, the consequences can be disastrous. Similarly, we only consider within this article, the equipment itself under safe and responsible operation, rather as we would not consider human error to reflect on the fitness for purpose of any other item of equipment.
The HSE makes clear in the introduction to its excellent Electrical Switchgear and Safety – A Concise Guide for Users that: In general, switchgear has a proven record of reliability and performance. Failures are rare but, where they occur, the results may be catastrophic. Tanks may rupture and, with oil-filled switchgear, this can result in burning oil and gas clouds, causing death or serious injury and major damage to plant and buildings in the vicinity. Failures of switchgear can also result in serious financial losses.
Having stated there is no law requiring users to replace aged switchgear, it is a legal requirement to provide management systems to ensure safety and minimise the risks of injury. To comply with this obligation it is clear that switchgear must be inspected, assessed and where necessary overhauled, repaired or replaced.
This having been said, de-skilling and cost reductions in some organisations have left them without the specialised knowledge needed to properly assess the function, potential risks and remedies where equipment is involved. Switchgear suppliers must therefore provide intelligent and conscientious assistance to users – which does not mean simply selling them some new equipment!
Let's take a look at some of the dangers specifically associated with the use of older switchgear. Among the most important are:
- Lack of knowledge – users may not have enough knowledge to be aware of the potential risks involved
- Overstressing – the switchgear may not be rated to handle present-day full load currents and fault levels
- Modifications – the manufacturer may have issued recommendations for modifications to ensure that the equipment remains safe to operate. It is essential these are implemented
- Dependent manual operating mechanisms – all switchgear currently in use must incorporate operating mechanisms that do not depend on the operator's strength and speed to make and break contacts. Any switchgear that does not meet this requirement is unfit for use
- Lack of proper maintenance – this is usually the result of oversight, but may also be due to limitations imposed by financial controllers in order to minimise shutdowns. It is important that maintenance of older switchgear takes into account the age and peculiarities of the equipment.
Addressing these issues involves implementing an effective switchgear management system. A very good starting point for this is Health and Safety Executive document HSG230 Keeping Switchgear Safe. The guidelines contained in this document define records that need to be kept and keeping these records will ensure that:
- The switchgear is not outside its managed life cycle
- The maintenance cycle and the maintenance work carried out has taken into account the age of the switchgear
- The maintenance has been fully and correctly completed
- A full maintenance history is available
- All restriction notices have been considered and, where necessary, appropriate actions have been implemented
- The Switchgear is known to fall in line with latest requirements, such as independent manual operation, anti-reflex handles
It is worth noting these records not only provide a framework for increasing the reliable and safe operation of the equipment, but also help to meet legal obligations, not least those related to ensuring that employees are protected from harm.
Safety in practice
Increasingly companies have become reluctant to operate older switchgear locally – particularly oil circuit breakers. With this in mind a minerals company recently ordered new vacuum oil replacement breakers, P&B Switchgear’s VOR-M, to replace old MV oil switchgear at its salt mining installation in Cheshire.
Vacuum retrofit breakers have been installed to replace 11kV oil breakers at a major pharmaceutical plant in Speke, Liverpool. This enables remote operation, as opposed to the local, manual, operation of the old switchgear. Not only does this ensure greater safety, but it also means switchgear can be operated without personnel having to don cumbersome arc flash protection clothing.
A major chemical company is also replacing old and obsolete air switchgear with 415V switchgear with modern compact air circuit breakers. During type testing of new retrofit circuit breakers to replace 415V circuit breakers from two well known, but now defunct, UK manufacturers, the original isolating contacts from both designs failed catastrophically under short circuit conditions. The fault level was within the rating of the equipment when supplied many years ago, indicating deterioration in performance of the contacts. Fortunately, P&B Switchgear was able to supply alternative type tested replacement isolating contacts with the circuit breakers to ensure the customer has a safe installation – this might perhaps start to ring warning bells with other switchgear users.
Reliability is key
Because diligently maintained and inspected switchgear of any age can be considered safe, a greater incentive to consider replacement or renewal of existing switchgear is often reliability. Reliability in sectors such as power generation, utilities, oil and chemical industries, transport and so forth is crucial. However, accurately assessing mean time between failures for switchgear is almost impossible. Hence, these industries often regard it as beholden upon themselves to mitigate worst case scenarios, however potentially unlikely. Many operators resort to establishing arbitrary maintenance procedures and time intervals based on their type of switchgear, age of equipment, its location and environment and so on. This usually involves high degrees of guesswork, certain assumptions and, if reliability is of paramount importance, a truncation of the service or inspection intervals. None of which is particularly efficient, but reliability trumps efficiency in such circumstances.
The main reasons for replacing switchgear are usually because the age of the equipment is causing a high level of maintenance, this in turn causing higher costs, lack of availability (reliability) and difficulty in locating obsolete spare parts. Some motives are to remove oil (safety) although some companies have elected to introduce remote operation on older switchgear as a cheaper way to improve safety by removing the need for a local operator. Safety may become a key driver for replacement in the future.
The use of the latest equipment with its inherent monitoring and reporting facilities, increases efficiency and hence reduces costs. However, in older plant, it is the reliability, rather than the automation, of the system that is the highest priority.
Reliability in practice
Most UK coal power stations were fitted with 11kV and 3.3kV air break switchgear when they were built in the 1960s. Over the past decade or so the circuit breakers have needed increased maintenance. That, coupled with the difficulty in obtaining spare parts for obsolete equipment, has led to many of the older breakers being retrofitted with P&B Switchgear vacuum circuit breakers. The overwhelming majority of these power stations have ranges of fully type tested retrofit vacuum breakers on most key circuits to increase reliability of operation. This is manifest in increased time between maintenance and in many cases, to increase the fault level to cater for additional generation being added over time. P&B designs have been type tested to well over 50kA rms, with peak making currents and DC components enhanced far above the original, or indeed, current IEC/BS requirements. Examples of this are at Ratcliffe, Cottam, Ferrybridge, Fiddlers Ferry, West Burton power stations to name a few.
The latest designs of breakers to replace oil types incorporate resin embedded vacuum interrupters and magnetic actuator operating devices for the ultimate in maintenance free, long life operation. This is especially suitable when frequent use is an important requirement, such as in process industries.
Costs are a key driver when assessing assets and running expenses. This is in greater focus even in the power generation sector, where costs have generally been less of a factor – reliability and safety ranking higher. It is understandably difficult to quantify costs and therefore economies in operating switchgear. However, the impact of greater reliability and perhaps just as significantly the ability to monitor and control the installations have made substantial savings that greatly offset the price of renewal of entire switchgear panels or the upgrading of them using the latest relay technologies.
Cost justification in practice
Replacing switchgear is never high on the list of capital requirements unless the previously discussed factors are important. As mentioned earlier there are guides issued by the likes of the HSE which assist users in the selection process of replace, refurbish or retrofit, but the cost of the options is usually a significant factor.
Often a straight forward approach is to simply remove the old switchboard and install a complete new one. This delivers a new installation compliant with the latest standards, but it is not usually the most cost effective option, even when the protection is to be replaced at the same time. Depending on the size and type of substation, replacing the old with new switchgear is likely to result in extra time and costs for building work, further costs and, of course, potential risk in disturbing or replacing cables that result in longer project timescales on site. It also requires a complete shutdown. Since in many cases the switchgear fixed portion is in good enough condition, these issues can be avoided with a circuit breaker retrofit option, even if the decision is to upgrade to modern protection relays.
Some companies consider the initial cost of a suite of retrofit breakers and argue this amounts to perhaps70% of the price of a new switchboard. However, when one takes into account the additional costs described earlier, the overall installed price for the retrofit option is typically nearer to 50%, with less disruption and reduced downtime. The case for organisations to select reliable partners has become increasingly important.