• Switchgear technology - Hybrid substation switchgear provides the best of both worlds

    Stephen Trotter, division head of ABB Power Systems UK, explains how hybrid switchgear  modules that combine the virtues of AIS and GIS technology can offer greater flexibility for substation design

    The term ‘hybrid' refers to the combination of both conventional air insulated switchgear (AIS) and the newer metal-clad gas insulated (GIS) switchgear. This hybrid solution, as found in ABB's Pass MO design - rated up to 170 kV, uses existing, tried and trusted GIS components together with a conventional and extremely reliable AIS bus to connect the various hybrid modules. All the necessary substation switchgear bay functions, including a circuit breaker, one or more combined disconnector/earthing switches, bushings for connection to single or double busbar systems and a current transformer are integrated in one compact module, eliminating the need for separate pieces of equipment for each function.

    Hybrid advantages
    The advantages of the hybrid switchgear design include:
    - AIS busbar: The AIS busbar is relatively inexpensive while offering proven reliability.
    - All live contacts in SF6: Experience has shown AIS disconnector switch contacts require relatively high levels of maintenance, while experience with GIS is exactly the opposite. The use of SF6 technology makes the hybrid switchgear virtually maintenance free, this combines with a high level of reliability to ensure a lower global life cycle cost.
    - Fewer switching elements: Use of GIS technology allows rationalisation of switching elements.
    - Factory pre-assembled and tested: The hybrid modules are fully pre-assembled and tested in the factory. This ensures a higher quality of finished bay than if it is assembled under site conditions, minimises installation time on site - typically two days per bay, reduces the possibility of delay due to adverse site conditions and there is less need for skilled resources on site.
    - Monitoring and on-line diagnostics: The integrated nature of the plant facilitates the use of electronic monitoring and on-line remote diagnostics.
    - Substation modularisation: A modular approach to substation design offers cost and time savings during the design and construction phases. The use of standardized components reduces the number of possible variations and hence the risk of design errors. More predictable costs also offers a higher level of confidence in the project estimation process.
    - Space saving and reduced civil works: The hybrid design can save up to 70% of the space normally required for a conventional AIS substation, while also reducing the need for civil works such as foundations, steelwork and cable trenching operations
    - Combined disconnector/earthing switch: Pass MO is equipped with a combined disconnector/earthing switch. The mechanism has a minimal number of mechanical components and is intrinsically reliable and maintenance-free.
    - Circuit breaker: The Pass MO circuit breaker is a single pressure interrupter that operates by means of the well known selfblast principle. The energy for interrupting currents is partly supplied by the arc itself, this reduces the energy the operating mechanism needs to provide by around 50% compared with a conventional puffer type circuit breaker.
    - Versatility: The Pass MO range offers a series of modules for HV substations including: single bus bar (SBB); double bus bar (DBB); double circuit breaker (DCB). It can also be installed as a high voltage bay on a mobile truck for use in emergencies or if work has to be carried out on existing HV bays.
    - Transportation: The Pass MO fits into a standard truck container and does not require any packaging. No special arrangements are needed for shipping and transportation, and once on site just a simple 30° rotation of the outer poles is needed for the final layout.

    Tight fit for Breamish Street substation
    Well over 2,000 Pass MO bays have been installed worldwide. Following its approval by the ENA (Energy Networks Association) one of the first UK projects to feature the range was CE Electrics UK's new 66/11 kV Breamish Street substation on a brownfield, urban site in Newcastle-upon-Tyne.

    The new primary substation is helping CE Electric UK to deliver an additional 18 MVA of firm capacity to meet the growing demand for additional power, and need for load transfer, created by the significant urban redevelopment programmes on the north bank of the River Tyne. The restricted space available presented a particular technical challenge, since the Breamish Street site is not only compact in size, it is also hemmed in on all four sides by a hotel, a pharmacy, a residents association and the 18th century St Ann's church.

    The space-saving capability of the design has been utilised to construct a new substation comprising two 66/11 kV 15/30 MVA CER transformers, a 66 kV in/out unit and a 13 panel 11 kV switchboard. A 66 kV feeder unit has also been installed at Fossway, the closest CE Electric UK substation.

    Providing vital construction space at Reading
    Hybrid switchgear has also provided an innovative interim solution for the new Scottish and Southern Energy (SSE) 132 kV indoor GIS substation at Reading, currently under construction by an ABB and Balfour Beatty consortium. The site presented a particular challenge as it was already completely full with time expired AIS switchgear that needed to remain in service until the circuits could be transferred to the new substation.

    At first, it appeared the only possibility would be to extend the site onto the local, heavily wooded, green space to offer the additional room needed for the construction of the new indoor GIS building. However, extending the site would have involved considerable planning time and expense and significant project delays.

    An innovative alternative was found by using ABB switchgear as a temporary measure to provide additional space to enable the new GIS building to be built within the existing site footprint. Firstly, ABB dismantled the generator circuit breakers that used to serve the old North Earley power station, which was demolished some years ago. This freed up just enough space to install the Pass MO modules to take over the operation of the AIS circuits at the far end of the site. This enabled the old AIS switchgear to be dismantled to make room for the new GIS substation. After all the circuits have been transferred to the new substation the Pass MO modules will be removed.

            
                         

  • Designed and built to automate switchgear

    LINAK’s iSwitch has been purposely designed and built to automate switchgear and is a complete turnkey solution.

    Advantages of the iSwitch began by listening to markets issues and their requirements and providing a solution, to name a few LINAK / iSwitch offers…
    -      Easy to install
    -      Manually operated without removing the iSwitch
    -      LINAK offers a complete solution
    -      Cost advantages (reduced instillation times / reliable feedback state etc)

    To summarise we have created and developed a modern approach to Network Automation offering a fit for purpose range of equipment that enables transparency in terms of local manual operation. We offer a competent solution which has been adopted and formally approved with UK and European based DNO’s.


    LINAK
    Tel: 0121 544 2211

    www.netline.linak.com

  • New low-voltage switchgear

    Rittal has significantly expanded the flexibility and modularity of Ri4Power. Combining Ri4Power low-voltage switchgear with designs 1 and 2-4 to form a single system technology, Ri4Power Form 1-4, allows switchgear manufacturers to fabricate every known form of internal subdivision from one single set of modules.

    Switchgear manufacturers now have access to three busbar systems for the different performance categories of one single low-voltage switchgear system. RiLine60, as a compact busbar system with component and connection adaptors, offers a solution for up to 1600 A for power distribution at the lower distribution level. Maxi-PLS provides a compact busbar system of 1000-4000 A that cuts installation time and Flat-PLS is a rugged busbar system for currents up to 5500 A, based on flat copper bars, meeting maximum requirements with its high short-circuit resistance.


    Rittal
    01709 704000
    www.rittal.co.uk
  • Feature switchgear - Checking switchgear is a really safe bet

    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.

  • Feature switchgear - Sf6 – Yesterday’s technology

    In the 1970s when SF6 (sulphur hexafluoride) was first used in MV switchgear, it seemed to be an almost ideal insulating and switching medium. Since then, the environmental and other hazards associated with SF6 have become increasingly apparent, leading to a shift towards alternative types of switchgear that eliminate its use with no cost or performance penalty. This means, says Alan Birks of Eaton’s Electrical Sector, that SF6 is now yesterday’s technology

    When the search was on in the 1960s to find a viable alternative to the potentially flammable, always messy and sometimes carcinogenic oils used in the MV switchgear of the era, SF6 must have seemed like a godsend. It combines excellent electrical properties with chemical stability and low toxicity. It’s non-flammable and  low in cost. Unsurprisingly, these very desirable characteristics lead to its widespread and enthusiastic adoption in MV switchgear.

    Unfortunately the picture was not quite as rosy as it at first appeared. In particular, as concerns about the environment and, in particular, global warming started to grow, it became all too clear that SF6 had significant potential for causing environmental damage.

    Global warming is the consequence of the greenhouse effect and this is usually associated with elevated levels of CO2 (carbon dioxide) in the atmosphere, which trap more of the sun’s heat. CO2 is not, however, the only culprit; there are many gases that are much more potent in trapping heat than CO2 and, unfortunately SF6 is one of them. In fact, SF6 is currently listed by the International Panel on Climate Change (IPCC) as the most potent greenhouse gas, with a global warming potential 23,900 times that of CO2. That’s not all – SF6 has an atmospheric lifetime of up to 3,200 years, so gas released today will affect the climate for a very long time.

    Clearly the release of SF6 into the atmosphere – which is virtually impossible to avoid when the gas is used, no matter how carefully it is handled – is highly undesirable. As a result, SF6 is on the Kyoto list of substances, the use and emission of which must be minimised. In fact, SF6 is now banned in most of applications, but it is still permitted in medium-voltage (up to 52 kV) and high-voltage (above 52 kV) switchgear. As a consequence 80% of the SF6 produced in the world today is destined for electrical applications.

    It can be confidently expected legislation will ultimately be introduced controlling the use of SF6 in switchgear. Some measures are already in place, including the voluntary programme of the Environmental Protection Agency in the USA and the F-gas regulations that were introduced in Europe in 2007. These legislative changes are already increasing the cost of maintaining switchgear that uses SF6 as well as starting to make its end-of-life disposal expensive and difficult.

    It is worth mentioning poor environmental characteristics are not the only shortcoming of SF6 – its use also gives rise to potential health and safety issues. While SF6 itself is usually considered to be harmless in normal concentrations, the derivatives that are inevitably formed by the arcs created during switching operations are another matter entirely.

    These by-products, which include HF, SOF2, SF4 and S2F10, are toxic. Granted they are produced in relatively small quantities during the normal operation of the switchgear, but they are likely to be present when switchgear is dismantled for maintenance or at the end of its life. Further, should a fault occur that causes an explosion in the switchgear, these toxic by-products are released into the surrounding area.

    We have established there is a strong case for avoiding the use of SF6 switchgear for new installations. Not only is it harmful to the environment, it is also likely to have a high lifetime cost, as the inevitable legislative changes make the maintenance and disposal of equipment that uses SF6 more and more expensive. But are there practical alternatives?

    In answering this question, it’s necessary to distinguish between HV and MV switchgear. When it comes to HV switchgear that operates above 52 kV, there are, at present, few viable alternatives to SF6 in its switching role. However, development is proceeding rapidly in this field and this situation can be expected to change in the not too distant future.

    However, for switchgear operating at below 52 kV, it’s a completely different story. Practical and affordable alternatives are readily available that make the use of SF6 completely unnecessary. The best of this new generation of SF6-free MV switchgear is based on vacuum interrupter technology used in conjunction with solid insulation.

    In addition to their almost negligible environmental impact, vacuum interrupters have many other characteristics to recommend them. Because of the way arcs behave in a vacuum – they constantly move from point to point on the electrodes rather than establishing themselves at a single location, and they are always extinguished at the first current zero – contact erosion in vacuum switching elements is almost non-existent. This has two important consequences. The first is that the switching elements require no maintenance, and the second is that they have very long working lives. The latest types are, for example, certified for 30,000 operating cycles.

    Modern vacuum interrupters are ideally complemented by solid insulation produced using cast epoxy resin technology. This approach allows the parts to be shaped specifically for the best possible insulation performance, with components such as busbars and vacuum interrupters integrated directly into the mouldings.

    The use of solid insulation also allows excellent control over electric fields in the switchgear. With conventional shapes for the primary components like busbars and other conductors in MV switchgear, the electric field is distributed in a manner that is far from uniform. This means there are areas with high field concentrations and, in these areas, there is risk of partial breakthrough. This can trigger avalanches leading to flashovers.

    With solid insulation, however, engineers with experience of breakthrough phenomena and field-steering techniques can arrange for the components and insulation used in the switchgear to be shaped in such a way that flashovers are eliminated entirely, while still achieving a very compact design.

    While the risk of internal arcs is very small with solid-insulated switchgear, it is impossible to say, as with any kind of switchgear, that there is no risk at all. However, solid-insulated switchgear has the additional important benefit that careful design can ensure that, if an internal arc event does occur, its environmental impact is minimised. This can be achieved by adopting single-pole construction, which means that the only conceivable type of internal fault is a single-phase short circuit, rather than a potentially more damaging phase-to-phase short circuit.

    In the best examples of solid-insulated switchgear, the impact of internal arc events is reduced still further by arc absorbers. These guide the gasses and smoke produced by the arc out of the panel and they also have a large absorbing surface that breaks up and filters the gases, greatly reducing their potential for causing damage and injury.

    Further benefits of solid-insulated switchgear over its SF6 counterpart include elimination of the costly and inconvenient routine pressure checks that are always needed with SF6 equipment; and low end-of-life disposal costs. In fact, the newest types of solid-insulated switchgear have been designed specifically to make re-cycling of the components used in them straightforward and inexpensive.

    It is now clear there is an alternative to SF6 switchgear in MV applications that not only eliminates the need to use this environmentally unfriendly gas, but also offers very significant benefits in its own right. Solid-insulated switchgear is safe, compact and very cost-effective, especially when lifecycle costs are considered. It offers dependable performance, it needs minimal maintenance and it has a very long service life. What possible reason can there be, therefore, for the continued use of MV SF6 switchgear?

    In truth, there is no reason. Specifiers and users of MV equipment would be well advised, therefore, to avoid SF6 equipment for all new installations. In addition, end users may wish to consider the benefits of replacing their existing SF6 equipment sooner rather than later, before the regulatory regime relating to greenhouse gasses tightens still further and pushes the costs associated with dismantling and disposing of such equipment sky high.

    A final thought for those who may be tempted to ignore this call to action – your option to do that may not last much longer! The use of SF6 in MV electrical equipment is still tolerated only because it is currently considered a special case, where there are no reasonable alternatives available. As we’ve seen, that’s no longer true, and it’s not hard to predict the relevant regulations will soon be changed to reflect this development.

    In short, SF6 is yesterday’s technology; it’s served its purpose but now it’s obsolete. SF6 offers no technical or financial benefits – in fact quite the opposite – so let’s confine SF6 MV switchgear to the one place where it still belongs. And that, of course, is a museum!

  • Switchgear technology - Guidance on the application of BS EN 61439-2

    Standards such as BS EN 61439-2, while ultimately beneficial to electrical designers and industry overall, can sometimes be confusing to the uninitiated. Here Andy Evans technical executive at Gambica, reports on the Controlgear Group Technical Committee’s (CGTC) view on how the standard applies to those distribution boards known as ‘panel boards’

    Concerns have been raised as to whether the casing around a switching contact mechanism can constitute a Form 4 enclosure as defined in Annex NA of BS EN 61439-2 and thus achieve a particular standard of separation between functional units.

    Panel boards are a type of distribution board, commonly consisting of a number of outgoing moulded case circuit breakers (MCCBs) or fuse switches, connected to a common busbar which in turn is fed from a single incoming MCCB. The outgoing connection can come from the MCCB device itself or onto a set of outgoing terminals associated with each outgoer. The arrangements made for the outgoing connections are many and various and have a big influence on the final Form of Separation.

    The starting point for switchgear design is the assumption the equipment must be safe to use for anyone who will have access to it during its lifecycle. This includes the fitters, engineers, maintenance personnel and machine operators as well as other people who shouldn’t touch the equipment but conceivably could, such as passers-by.

    Annex NA to BS EN 61439-2 defines the performance criteria for an assembly to Form 4 as follows:

    Main Criteria
    Separation of busbars from functional units and separation of all functional units from one another, including the terminals for external conductors, which are an integral part of the functional unit.

    Sub Criteria, Form 4a (Types 1-3)
    Terminals for external conductors (are) in the same compartment as associated functional unit.

    Sub Criteria, Form 4b (Types 4 – 7)
    Terminals for external conductors (are) NOT in the same compartment as associated functional unit, but in individual separate, enclosed, protective spaces or compartments.
    In order to apply these definitions, one has to answer the question, ‘What constitutes a functional unit and how is the necessary separation, as defined in the criteria above, created?’

    The answer to this question is also provided in BS EN 61439-2, where a functional unit is defined as “A part of an assembly comprising all the electrical and mechanical elements that contribute to the fulfilment of the same function”.

    Although alternative interpretations are sometimes given, BS EN 61439-2 actually states that the integral housing of a device, for example a moulded case circuit breaker, is sufficient to satisfy the separation requirements as follows: 
    8.101 Internal separation of PSC-ASSEMBLIES (power switchgear and controlgear assemblies)

    Typical arrangements of internal separation by barriers or partitions are described in Table 104 and are classified as forms (for examples, see Annex AA).

    The form of separation and higher degrees of protection shall be the subject of an agreement between assembly manufacturer and user.

    PSC-assemblies can be divided to attain one or more of the following conditions between functional units, separate compartments or enclosed protected spaces:
    - protection against contact with hazardous parts. The degree of protection shall be at least IP XXB;
    - protection against the passage of solid foreign bodies. The degree of protection shall be at least IP 2X.

    Note: The degree of protection IP 2X covers the degree of protection IP XXB.
    Separation may be achieved by means of partitions or barriers (metallic or non-metallic), insulation of live parts or the integral housing of a device e.g. a moulded case circuit breaker.
    It should be noted the Form of Separation is one of the design aspects that is ‘subject to agreement between manufacturer and user’.

    So, to satisfy the main criteria for Form 4, one alternative is to merely use an MCCB which by definition has a moulded case enclosing the electrical and mechanical parts necessary for it to fulfil its function. In this case, the terminal compartment may also physically form one of the constructional elements of the MCCB device.

    To effect this arrangement, a means of shrouding the terminals and connected cable glands to ensure a minimum of IPXXB is necessary. Form 4 Type 5 indicates this may be done by use of insulated coverings. Forms 4 Type 6 and Type 7 require the separation via metallic or non-metallic rigid barriers or partitions.

    So, again, a suitably designed MCCB device can satisfy both the main criteria, for Form 4 and the sub-criteria for Form 4b, and depending on the materials used to form the termination chamber, can provide Form 4 Type 5 or 6 arrangements.

    One key issue to note is neutral (N) conductors, as they contribute to the fulfilment of the same function, form part of a particular functional unit and, in respect of Forms of Separation, must be treated as part of the functional unit. To this end, each outgoing way must have its own individual N connection, usually alongside the phase connections, and not be connected at a common N bar or terminal. 

    For four pole functional units, this is not normally an issue but in the case of a TP&N system, it’s a little more complicated. It is usual for a triple pole MCCB, for example, to have a separable neutral link mounted immediately adjacent to the MCCB to allow connection of all external cables in the same protected space, assuming adequate shrouding of all four terminals. For this arrangement to remain within the definitions of a functional unit and separation, multiple components should be logically arranged without gaps  so that they are readily seen as being within one space.

    A common N termination point arrangement cannot be deemed to be Form 4 as there is no separation of the terminals for external N connections for each functional unit in this case.

    There is no distinction in BS EN 61439-2 between a Form 4 declaration where MCCB enclosures are used to define separation of functional units in a single enclosure compartment and that employing MCCB devices mounted in separate compartments of a multi-compartment PSC- assembly. Both can be declared Form 4 separation and both meet the performance requirements for separation. However, separation is not the only criterion to be considered. Regardless of the form of separation employed or how it is achieved, all assemblies must meet all the other safety and performance criteria laid down in the standard, for example; short- circuit including emissions from devices, temperature rise, and protection against electric shock.

    BS EN 61439-2 gives only typical arrangements of internal separation; fundamentally the objectives of the separation and how it is achieved is a matter for agreement between the customer and the manufacturer. As a result, the customer should give careful consideration to the needs of his application, for example maintenance requirements.

     
    Gambica is the trade association for instrumentation, control, automation and laboratory technology in the UK. It has a membership of over 200 companies including major multinationals in the sector and a significant number of smaller and medium sized companies.

    It covers the following five principal sectors of the
    industry:
    - Industrial automation products and systems  
    - Process measurement and control equipment and systems
    - Environmental analysis and monitoring equipment
    - Laboratory Technology
    - Test and measurement equipment for electrical and electronic industries

    Permission to reproduce extracts from BS EN 61439-2 is granted by BSI.  British Standards can be obtained in PDF or hard copy formats from the BSI online shop: www.bsigroup.com/Shop.

  • Switchgear Systems launches new bypass switch range

    Switchgear Systems, one of the UK’s leading suppliers of bespoke high current, low voltage switchgear, is responding to steep demand from the Voltage Optimisation industry, for bypass switches to safeguard installations on ever-larger facilities.

  • Advertorial - The primary choice for MV switchgear

    ABB's UniGear 500R compact medium voltage switchgear with removable circuit breaker offers the highest levels of safety and reliability combined with simplicity of installation and ease of use for a wide variety of primary distribution applications

  • Safety and medium voltage switchgear

    Because of the high energy levels and high voltages involved, there will always be potential hazards involved in working with medium voltage (MV) switchgear. Modern developments are, however, significantly reducing these hazards, helping to make MV switchgear safer while also enhancing its reliability. David McCabe of Eaton’s Electrical Sector explains

    Let’s be very clear from the outset, the key to safe working on MV equipment of any kind is appropriate training. MV equipment is not forgiving of mistakes, the consequences of which can be literally lethal. Work on MV equipment must, therefore, only be carried out by authorised and competent personnel who are properly trained and qualified. Having said that, there are practical measures that can be taken to minimise risk. Let’s take a look at some of these.

  • Switchgear safety conferences in demand

    EA Technology, technical author of the Health & Safety Executive publication HSG 230 Keeping Electrical Switchgear Safe, will be hosting an additional switchgear safety conference on 6 December from its facility in Chester.

    The Keeping Electrical Switchgear Safe (KESS) conferences have been designed to share best practice across the industry with industrial and commercial owners as well as distribution network operators and switchgear equipment suppliers.

  • A new name in LV switchgear

    Havells is a new name in the UK for low voltage circuit protection and control. The company has launched an exciting new range of consumer units, which will shortly be followed by a whole raft of new products including Type A and Type B distribution boards and MCCB panelboards.

    Many people will have heard of Havells Sylvania, which is well known in the lighting industry for its Sylvania, Concord and Lumiance branded products.  What is not so well known is that in recent years it has supplied an estimated 50 million poles of circuit breakers as OEM products to leading UK electrical companies and that the parent company, Havells India is a fast-growing global manufacturer of residential and commercial switchgear giving it a unique advantage when it comes to entering this highly competitive market.

  • Low voltage switchgear

    Eaton has launched its new Power Xpert CX, an IEC low voltage switchgear with a range up to 4000 amperes (A). Power Xpert CX is compact, ergonomic and flexible and provides reliable motor control and power distribution functionality for industrial and commercial installations.

    The innovative design, combined with Eaton's expertise in low voltage applications, brings a new, reliable platform that can be at the heart of any motor control or power distribution system and is especially suitable for applications where the delivery of electrical energy is business critical such as those found in the water, pharmaceutical, food and beverage, infrastructure, pulp and paper, mining and steel industries, as well as industrial facilities and commercial buildings.

  • A new name in LV switchgear

    Havells is a new name in the UK for low voltage circuit protection and control.  The company has launched an exciting new range of consumer units, which will shortly be followed by a whole raft of new products including Type A and Type B distribution boards and MCCB panelboards.

  • Low voltage switchgear

    Eaton has launched its new Power Xpert CX, an IEC low voltage switchgear with a range up to 4000 amperes (A). Power Xpert CX is compact, ergonomic and flexible and provides reliable motor control and power distribution functionality for industrial and commercial installations.

  • Switchgear condition assessment and monitoring

    Modern approaches to switchgear maintenance requires non-intrusive testing to identify any developing problems that could, if left undetected, lead to expensive disruptive failures.

    Hawker Siddeley Switchgear, as part of its non-intrusive condition assessment and monitoring service, offers customers partial discharge mapping, thermal imaging, battery condition check, environmental checks and switchgear general condition reports.

  • Non-intrusive switchgear condition assessment and monitoring

    Modern approaches to switchgear maintenance requires non-intrusive testing to identify any developing problems that could, if left undetected, lead to expensive disruptive failures.  Hawker Siddeley Switchgear, as part of its non-intrusive condition assessment and monitoring service offer customers partial discharge mapping, thermal imaging, battery condition check, environmental checks and switchgear general condition reports.

  • Switchgear service centre

    Understanding that long-term aftermarket support is as vital to customers as the product itself, Hawker Siddeley Switchgear has developed a highly-important new arm to its Aftermarket services.

  • ZX1.5-R is the primary switchgear choice for railway power distribution

    ABB’s ZX1.5-R primary medium voltage GIS (gas insulated switchgear) solution has been developed to meet the specific needs of railway applications. Its design is the latest evolution in the ZX family of switchgear that is well established in industrial and utility installations, and it inherits all the key features of this well proven platform.

  • Gas insulated switchgear (GIS) shrinks in size and increases performance

    Safe, reliable electricity supplies depend on the circuit breakers that protect power grids in the event of a short circuit. Historically, these circuit breakers, installed in power plants and substations, were air-insulated. Air-insulated switchgear (AIS), depending on the rating, requires a minimum clearance between various active parts and earth - in the order of tens of metres, which means a large area is needed to

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Continued support for switchgear installations

    Switchgear-retrofit.com has been set up to serve the increasing demand from switchgear users and operators who require continued support for their switchgear installations. We take a very different view to the ongoing use and support of switchgear than that which is taken by traditional switchgear manufacturers.

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