Civil Design and Construction of 132kv 66kV and 33kV Substation

Guidance Document

Civil Design and Construction of 132kV, 66kV and 33kV Substations

Version:

2

Date of Issue:

July 2009

Author:

Keith Nutter

Job Title:

Civil Engineer

Approver:

Mark Simpson

Job Title:

Network Standards Manager

Guidance Document Civil Design and Construction of 132kV, 66kV and 33kV Substations

Revision Log Version 2

Keith Nutter

July 2009

Version 2 DRAFT

Keith Nutter

May 2009

Keith Nutter

February 2007

Draft Update Version 1 First Issue Version 0.1

Prepared by Keith Nutter

Date November 2006

First Draft

Version: 2

Date of Issue: July 2009 The master version of the this document resides in the E.ON UK Documentum database CAUTION – any other copy may be out of date

© Central Networks plc

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CONTENTS 1.

INTRODUCTION .................................................................................................................. 5

2.

SCOPE ................................................................................................................................ 5

3.

CHOICE OF SITE .................................................................................................................. 5

3.1

SIZE AND SHAPE ................................................................................................................................................... 5

3.2

GROUND CONDITIONS ........................................................................................................................................ 6

3.2.1

Substrata nature and bearing capacity ...................................................................................................... 6

3.2.2

Ground water levels ............................................................................................................................................ 6

3.2.3

Presence of contaminants ............................................................................................................................... 6

3.2.4

Soil resistivity profile .......................................................................................................................................... 7

3.3

PLANNING CONSENT ........................................................................................................................................... 7

3.4

BUILDING REGULATIONS .................................................................................................................................. 7

3.5

SITE SURVEY ........................................................................................................................................................... 8

3.6

FLOOD RISK ............................................................................................................................................................. 8

4.

SITE LAYOUT REQUIREMENTS ........................................................................................... 8

4.1

OPERATIONAL COMPOUND.............................................................................................................................. 9

4.1.1

Plant ........................................................................................................................................................................... 9

4.1.2

Spacing ................................................................................................................................................................... 10

4.2

BUILDINGS ............................................................................................................................................................ 12

4.2.1

Switchrooms......................................................................................................................................................... 13

4.2.2

Control Room ....................................................................................................................................................... 14

4.2.3

W.C. ........................................................................................................................................................................... 15

4.2.4

Store......................................................................................................................................................................... 16

4.2.5

Mess Room

4.3

OTHER ...................................................................................................................................................................... 16

4.3.1

Access ...................................................................................................................................................................... 16

4.3.2

Ancillary Plant ...................................................................................................................................................... 17

4.3.3

Services ................................................................................................................................................................... 17

5.

DESIGN AND CONSTRUCTION ........................................................................................... 18

5.1

GENERAL ................................................................................................................................................................ 18

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5.2

STANDARDS .......................................................................................................................................................... 19

5.3

BUILDINGS ............................................................................................................................................................ 19

5.3.1

General.................................................................................................................................................................... 19

5.3.2

Walls......................................................................................................................................................................... 20

5.3.3

Floors ....................................................................................................................................................................... 21

5.3.4

Windows and Ventilation ............................................................................................................................... 22

5.3.5

Roofs ........................................................................................................................................................................ 22

5.4

FENCING ................................................................................................................................................................. 23

5.5

TRANSFORMER FOUNDATIONS AND BUND WALLS ............................................................................ 23

5.6

EARTHWORKS/FOUNDATIONS ...................................................................................................................... 23

5.7

CONCRETE .............................................................................................................................................................. 24

5.8

FORMWORK AND REINFORCEMENT .......................................................................................................... 24

5.9

STEELWORK .......................................................................................................................................................... 25

5.10

EQUIPMENT SUPPORT STRUCTURES .......................................................................................................... 25

5.11

CABLE DUCTS / TRENCHES .............................................................................................................................25

5.12

DRAINAGE.............................................................................................................................................................. 26

5.13

SITE SURFACING ................................................................................................................................................. 27

5.14

ROADS AND PATHS ............................................................................................................................................ 28

5.15

NOISE HOUSINGS ............................................................................................................................................... 28

5.15.1 Design ..................................................................................................................................................................... 28 5.15.2 Construction ......................................................................................................................................................... 29 5.16

SECURITY ................................................................................................................................................................ 30

5.17

FIRE PROTECTION ............................................................................................................................................... 30

5.18

DOORS ..................................................................................................................................................................... 31

5.19

HEATING AND LIGHTING ................................................................................................................................. 31

6.

APPENDICES

Appendix A: Fire Segregation at Primary and Grid Substations. Appendix B: Substation Drainage Appendix C: Transformer Foundations and Bund Walls. Appendix D: Doors for Primary and Grid Substations Appendix E: Heating, Lighting and Small Power at Primary and Grid Substations Version: 2



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1.

INTRODUCTION This document details Central Networks requirements for the design and construction of 132kV, 66kV and 33kV Primary and Grid Substations. This document must be read in conjunction with the Central Networks Network Design Manual, Distribution Safety Rules, and other relevant Central Networks Policies and Guidance.

2.

SCOPE This document applies to the design and construction of all Primary and Grid substations at 132kV, 66kV and 33kV that are to be adopted onto the CN Network. It is to be used by Central Networks staff, Energy Services staff, and External Services Providers. For substations that are constructed on behalf of customers, and are not adopted as part of the CN network, then certain amendments relating to future requirements apply. These are noted within the body of the document. This document is also to be used where alterations are required to existing Primary and Grid substations, although it is accepted that it will not be possible to meet all requirements in some of these cases, due to existing site constraints.

3.

CHOICE OF SITE This section deals with physical factors of the proposed site that can significantly affect its viability as a substation location. These factors must be considered before construction commences, and preferably before the land is purchased. In addition to the factors listed below consideration should also be given at an early stage as to how the Construction phase work will be undertaken. In particular the requirements of the Construction (Design and Management) Regulations and the Site Waste Management Plans Regulations should be considered.

3.1

SIZE AND SHAPE The area of land to be purchased must be of a suitable size and shape to accommodate the present and future needs as set out in the Site Layout Requirements section. Care must be Version: 2



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taken to ensure the plot is suitable in all respects and that both existing and potential future uses of surrounding land have been considered. In addition suitable access must be available from the public highway. This may require construction of a simple junction with an existing road, or may require the construction of a relatively long access road. In either case the access must be suitable for both ’day to day’ use, and also for delivery of large plant items. 3.2

GROUND CONDITIONS A Geotechnical Ground Investigation Survey should be carried out to determine the following:-

3.2.1

Substrata nature and bearing capacity The properties of the existing ground can have a major and costly impact on ground working and foundations. Without knowledge of the ground conditions, foundation design and excavation requirements would have to be based on assumptions. If these assumptions are incorrect, any subsequent changes required will severely impact on cost and programme. In some cases where poor ground conditions are encountered, then specialist design and construction will be required, such as piling and de-watering.

3.2.2

Ground water levels A high water table might affect foundation design and construction. It may also impact on ground working methods which again can cause increased costs and programme delays. A high water table may also impact on cable laying requirements.

3.2.3

Presence of contaminants Contamination of land can lead to expensive clean up measures or to long term remedial / monitoring requirements. Contaminants may include: • •

Asbestos – Costly specialist removal. Heavy metals – All excavated material removed from site will be classed as contaminated waste, the disposal of which carries a premium price. Version: 2



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• •

Oils – Can migrate, via ground water, to adjacent properties and lead to the possibility of future litigation. Gas – either naturally occurring from ground conditions, or from previous uses of the land.

In addition to cost and programme implications, the presence of contaminants may present potential health risks during both the construction stage and subsequent operation of the site. It should be noted that if contamination is discovered after the purchase of the land, then Central Networks will be responsible for clean up costs, unless the original polluter can be identified. 3.2.4

Soil resistivity profile This is required to determine if the site is able to support an adequate earthing system. The resistance of the substation earth will depend on the soil resistivity and the area of the earth nest. High soil resistivity requires a large site. To determine the earthing requirements calculations are required in accordance with the Central Networks Earthing Manual. A ‘Hot’ site in terms of earthing has safety and operational implications – touch, step and transfer potentials have to be carefully controlled.

3.3

PLANNING CONSENT If the substation is to be located on an existing operational site, then it is possible that a formal Planning Consent will not be required. To determine whether a site is exempt, reference should be made to Schedule 2 (Class G) of The Town & Country Planning (General Permitted Development) Order 1995. In all other cases Planning Consent will be required. If the site is located in a sensitive area, i.e. residential, conservation area, national park, etc, it is preferable to obtain an Outline Planning Consent before fully committing to purchase of the site.

3.4

BUILDING REGULATIONS Operational Buildings within substations may be exempt from requiring Building Regulation approval. They are covered by Building Regulations 2000; Regulation 9; Schedule 2; Exempt Buildings and Work – Class II; Buildings not frequented by people. Version: 2



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However there are several other instances, such as connection to existing drainage systems, which would require a submission under Building Regulations. It is Central Networks policy that the design and construction of all operational buildings should comply fully with current Building Regulations, even if approval is not required. Substations that are designed and build by ESP Contractors and Third Party Developers shall be subject to full formal Building Regulations Approval, and copies of Consents supplied to Central Networks to prove compliance with this requirement. 3.5

SITE SURVEY In order to achieve the most practical and cost effective site layout, a detailed topographic site survey should be carried out, ideally prior to the purchase of the land. The site survey information will assist with the design and layout of the site, and will identify issues with ground levels and suitable access.

3.6

FLOOD RISK All new Primary and Grid substations should be located and constructed with regard to the potential flood risk at the site. See the separate policy on flood risk for further guidance.

4.

SITE LAYOUT REQUIREMENTS This section deals with the factors that need to be taken into consideration when designing the substation layout. The components that make up the layout are generally the Compound (may be only a transformer compound or may also contain open terminal busbars and equipment), Building, Access Roads and Fencing. The layout must take into account factors such as practical use of space available, operational requirements, safety requirements, and inspection and maintenance requirements. Before considering possible layouts, the following basic system information is required:•

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Plant and equipment to be accommodated & maintained – type, quantity and electrical safety clearances.



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• •

Likely need for future expansion. Cables – type, number & site exit/entry locations and directions.

The layout should be prepared using this information, together with the information available from section 3 above, to give a practical, safe, cost effective solution.

4.1

OPERATIONAL COMPOUND

4.1.1

Plant At 33kV sites with cable connected transformers there may also be a need for NERs, NER switches, Fault Thrower cubicles and Ring Main Units. At 33kV and 66kV sites with open terminal busbars and plant, then the layout may also need to include for Busbars and supports, Circuit Breakers, Fault Throwers, etc, together with appropriate ancillary equipment. At 132kV sites the layout will be dependent on the individual requirements for the substation. The majority of sites will be open terminal sites with similar plant to the 33/66 open terminal sites. Some 132kV substations may be constructed as ‘indoor’ sites utilising GIS switchgear. Where possible, substations at all voltages shall be designed with sufficient space to incorporate an additional transformer, and switchgear bay where required, at a later date. (Two transformer sites shall therefore have space for a third unit). 132kV sites may require additional measures to incorporate future expansion (e.g. space for four transformers with two installed initially). These requirements will be specified by Network Strategy at the planning stage. 33kV sites may be designed with 12/24MVA or 20/40MVA transformers. However the transformer foundations and bunds shall be designed to accept both 12/24 and 20/40 units. This will allow subsequent upgrading with minimum additional work. The above requirements may be relaxed where the substation is for a Customers use only and will not supply distribution load. In these cases the sites can be designed for the exact requirements of the Customer. Version: 2



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At 66kV and 132kV sites transformer foundations and bunds shall be designed for the actual units to be installed, there is no requirement to incorporate any possible upgrading. 4.1.2

Spacing When designing the compound layout consideration must be given to the following factors: 4.1.2.1 Fire The clear distance between transformers or between a transformer and any other oil-containing equipment shall be not less than 12m at 132kV, or 6m at 66kV and 33kV. Where transformers are in noise enclosures this separation may be reduced but should be not less than 6m at 132kV, or 4m at 66kV and 33kV. If this separation cannot be achieved then the provision of a fire barrier wall will be required. This structure shall have a minimum fire resistance of 4 hrs at 132kV, or 2 hrs at 6kV and 33kV. There shall also be adequate fire separation between the transformers and control buildings. This shall be not less than 6m. For full details of fire segregation requirements see Appendix A: Fire Segregation at Primary and Grid Substations. 4.1.2.2 Touch Potential In situations where there is more than one earthing system (fence earthed separated from main earth grid), it is essential that separately earthed plant, structures, etc are sufficiently spaced so that they cannot be touched simultaneously. To prevent this, a horizontal separation of 3.0m is preferred, and a minimum separation of 2.0m must be provided. In certain circumstances insulated fence panels may be required. Refer to the Earthing Manual for full details. 4.1.2.3 Access & Maintenance All plant and equipment shall be provided with sufficient free space to permit safe operation and maintenance. Version: 2



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Plant over 2.0m high (which will include all transformers) will require full access by powered mobile access equipment. Depending on compound layout and transformer orientation, vehicle access routes within the compound may be required. Spacing of equipment must be such that access for maintenance is possible with adjacent plant / circuits live. Refer also to the guidance given in the Power Systems Operation Manual, section 6.2. Consideration must be given to means of transformer installation and removal with the other transformer(s) live. The provision of removable compound fence panels (i.e., with bolt down posts) will usually be necessary 4.1.2.4 Cable Routing Cables need to be as accessible as possible, in case of future faults, jointing, etc. Where cable runs beneath structures cannot be avoided they must be ducted. It is likely that cable/duct excavation and laying will not occur until after the structures have been completed. The potential risk of undermining and/or destabilising the structures must be considered when planning cable routes. If cable trenches are provided, then the trench and covers must be designed to support the appropriate applied loading. This may be pedestrian loading only, or the weight of any plant or vehicles that may need to pass over them for the purpose of equipment installation and/or maintenance. 4.1.2.5 Fence Layout In addition to the requirements above for positioning the fence with regard to touch potential and access and maintenance requirements, the security of the site must be considered when designing the layout. The compound fence must be inset from the boundary of the site by a minimum distance of 2 metres. This 2 metre gap prevents neighbours from constructing anything which may be used as a climbing aid and therefore compromise the security of the site. See section 5.15 for further guidance on site security.

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All compounds must have at least two points of access / egress. On sites with small cable connected transformer compounds these can be personnel gates, of minimum width 1.675 metres (centre to centre of gate posts), with removable fence posts and fence panels provided to cater for transformer removal and plant maintenance. On sites of open terminal design, one access / egress must be a set of double gates of minimum width 4.57 metres (centre to centre of gate posts) to allow access for maintenance vehicles. For full details of fencing requirements see separate policy document: Specification for Fencing for Grid, Primary and Distribution Substations. 4.2

BUILDINGS All sites will usually require a building to house switchgear, control equipment, etc. The building shall be segregated from the main compound area. This can be achieved either by placing the building outside the compound fence area, or by placing the building within the security fence area, but providing a segregating fence between the building and the compound plant. Exact layout will depend on site requirements, including an assessment of security issues. Buildings will consist of: Switchroom(s) for the indoor 11kV or 33kV switchgear Separate control room for relay panels, batteries, LVAC board etc. Separate store room for cones, chain, etc. Separate WC Mess Room – to be provided at certain 132kV substations only (see below) There is some flexibility in the provision of toilet and mess room facilities, and each proposed installation shall be subject to a cost/benefit assessment before a decision is made. In some rural locations the provision of a mains water supply will be uneconomical, and the use of a suitable ’rainwater harvesting’ may be considered as an alternative. All rooms must have suitable segregation to meet fire protection requirements. Separate external access will normally be provided to each individual room; there must be no direct

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connecting doors between rooms. For larger sites the use of a central ‘lobby’ may be utilised (see below). On smaller sites the above requirements will usually result in a ‘linear’ building layout with switchroom, control room and store/WC all in one line. For larger sites, or sites with space restrictions, other layouts may be preferred. On larger sites with several rooms the provision of a central lobby may be considered giving access to control and switch rooms. There MUST still be segregation between rooms with separate entrances from the lobby area, all fitted with suitable fire doors. If convenient the WC and mess room (where provided) can also be accessed from the lobby. On some small sites, such as switching compounds, there may be no requirement for a building, or the building may be reduced in size. Site specific assessment will be needed to identify exactly what is required. The provision of a WC shall be carefully assessed for these sites, and there is also NO requirement for a mess room. 4.2.1

Switchrooms At 33/11kV substations switchrooms shall usually be designed to accept one of three options for the 11kV switchgear. Either 13, 17 or 21 panel switchboards will be provided. For certain projects the Network Planning Section will specify an alternative number of panels. No space allowance is to be made for future additional units, the number of panels to be installed initially must take into account future requirements where known. Regardless of initial requirements, the building must be capable of accommodating 2000 amp switchgear. There are also some 11kV distribution or consumer sites with requirements for smaller switchboards, not the ‘standard’ options listed above. The design of these sites is covered in a separate document. At 132/11kV, 66/11kV and 132/33kV sites the 11kV and 33kV switchboards are to be designed to the requirements of the individual site. Again no space should be allowed for future units, but the number of panels installed initially must take into account known future requirements. If 33kV and 11kV switchboards are provided at the same site then they must be in separate rooms.

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All switchboards shall be broken up into discrete ‘sub-boards’ with no more than two transformer incomers on each. Each ‘sub-board’ shall be housed in a separate switchroom, segregated by fire barrier walls with no interconnecting doors. Where modifications are carried out to existing sites, the above design rule for segregation of switchboards shall be complied with wherever reasonably practicable. For general guidance: Where additional switchboards with incomer(s) are added to existing sites already having two or more incomers in one switchroom, the new switchboards shall be segregated by providing new switchrooms. The new switchroom(s) shall either be separate from existing switch-houses or fire barrier walls shall be provided between switchboards. Where existing switchboards are being replaced within existing switch-houses and more than two incomers are involved, then where it is reasonably practicable to do so, the new switchboard shall be split and fire barrier walls provided. There must be sufficient space around plant and equipment for its safe operation, testing and maintenance, and to allow for future replacement of an individual panel. To accommodate these requirements the following minimum clearances must be provided: Rear 1100mm End 1100mm Front The greater of: Switchgear panel depth +500mm, OR 2000mm Head The greater of: IEC test requirements, OR 1000mm Entrance and exit doors must be sized and positioned to enable pedestrian access, equipment access, and statutory fire escape requirements. Exact positioning of doors will be dependant on individual site layout. For full details of clearances, escape requirements and fire segregation requirements see Appendix A: Fire Segregation at Primary and Grid Substations. 4.2.2

Control Room Control rooms shall be designed to accommodate the following equipment as a minimum: Transformer relay and AVC panels (including space for future units where appropriate) Telecontrol panel and outstation Substation battery Telecontrol battery Version: 2



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Switchgear local control panel Feeder and bus section relay panels as required LVAC board Intruder alarm panel Melamine top table, 1200mm by 800mm 2 No canteen style polypropylene stacking chairs Telephone Four drawer filing cabinet Safety notice board Key cabinet / key safe Fire point with extinguishers Door mat – recessed type for ‘computer’ floors, otherwise standard surface mat with non slip backing Equipment shall be positioned so there is adequate clearance for installation, inspection, maintenance and future replacement. Specific minimum distances are required to the front and rear of control and relay panels, see Appendix A: Fire Segregation at Primary and Grid Substations for full details. The height of the control room will usually be the same as the adjacent switchroom, but as a minimum there must be 500mm clearance above the relay / control panels. Suitable provision must be made for personnel and equipment access and exit. Usually one door will be suitable for all requirements but on some larger sites two doors may be required. The control room access door must be clearly marked as this will be the normal substation building entry point providing access to the intruder alarm panel. 4.2.3

W.C. The WC shall contain: WC suite Wash hand basin with cold tap and instantaneous electric hot water heater Separate bib tap for hose connection Stop tap for incoming water supply Warm air hand dryer Toilet roll holder Version: 2



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Coat hook Extractor fan with over-run timer connected to lighting circuit Door mat with non slip backing. 4.2.4

Store The store room is required for the storage of cones and chain, temporary earths, etc. On 33kV and 66kV sites a room with a minimum floor area of 3 square metres shall be provided. On 132kV sites a room with a minimum floor area of 6 square metres shall be provided.

4.2.5

Mess Room Where mess rooms are provided the nominal size shall be 3.5m by 3.0m. The following items shall be provided: Stainless steel single bowl and drainer sink top Double door cupboard unit to support sink top Pillar tap for cold water supply Instantaneous electric hot water heater Warm air hand dryer 225mm Extractor fan with manual switch Melamine top table, 1200mm by 800mm 4 No canteen style polypropylene stacking chairs 4 No coat hooks on timber rail Door mat with non slip backing.

4.3

OTHER

4.3.1

Access Suitable access must be provided form the public highway to the substation site, and also within the substation site. All access roads must be suitable for the delivery of large, heavy Version: 2



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plant items. In addition consideration shall be given for the positioning of a crane to offload plant items, including transformers. For 33kV and 66kV sites a minimum road width of 4.0 metres must be provided, and for 132kV sites this should be a minimum of 4.5 metres. These dimensions are for straight sections of road; bends will require either a greater road width, or provision for ‘overhang’ of large plant delivery vehicles. Exact requirements will depend on site layout and access route. Within the substation site a turning area shall be provided, suitable for a long wheel base panel van. Where feasible an area for the parking of two cars or vans, which does not block the main access, should also be provided. This can either be part of the existing road layout or a separate area of hardstanding. The design of the junction of the substation access road with the public highway also needs careful consideration. Designs should take into account sight lines and space required for turning into / out of the access road. 4.3.2

Ancillary Plant In addition to the main plant items within the compound there may be a requirement for a local distribution substation. Where required, allowance shall be made for this within the site layout, ensuring that access is available for installation of the package switchgear.

4.3.3

Services In addition to requirements for cabling across the site (power and multicore cables), provision must also be made for other services. A water supply, surface water drainage (including interceptor), foul water drainage, and telecoms connection will usually be required.

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5.

DESIGN AND CONSTRUCTION

5.1

GENERAL All aspects of the civil works shall be designed to provide a low maintenance durable end product suitable for the purpose intended. Particular emphasis shall be placed on security of the site. Design life for structural elements shall be a minimum of 40 years. In accordance with the requirements of the Construction (Design & Management) Regulations the design of buildings and structures should be carried out to ensure that construction, maintenance and demolition may be carried out in a safe manner. It is also important that any buildings are built to a high standard and that the finished building shall be designed to be aesthetically acceptable. The design of the civil works and the specification of civil materials shall take into account the environmental impact of all elements. Where possible, ’environmentally friendly’ materials and methods of construction should be incorporated into the works. E.ON UK has a Biodiversity policy statement which actively supports biodiversity across the business. Central Networks supports this policy on Primary and Grid substations by integrating biodiversity considerations into the design process. Planners and Designers should make provision for these where appropriate. See the Central Networks Environment Manual for further information. Emphasis is placed upon prevention and limitation of fire damage. Measures are specified in Appendix A: Fire Segregation at Primary and Grid Substations, and these shall be adopted as a minimum requirement. This document shall also be used as a guide for clearances around switchgear and other equipment. Power cables and control cables shall be routed and/or segregated such that minimal loss of control or supplies occurs in the event of fire or damage. With modern SF6 and vacuum switchgear there is no requirement to incorporate any blast relief measures into the building construction. Where existing oil filled switchgear is used in a building requiring alteration or extension then consideration shall be given for the need for blast relief measures.

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5.2

STANDARDS All design and construction including all materials, testing and other procedures shall be undertaken in accordance with appropriate Electricity Supply Industry Standards and current British / European Standards.

5.3

BUILDINGS

5.3.1

General Buildings may be either: •

Brick / block construction with a variety of different roof constructions.

•

Steel portal frame design with profile steel sheet cladding, and brick / block perimeter walls to a minimum height of 2.0 metres.

•

Other proprietary design, such as a panel system, subject to the approval of Network Standards.

Access to plant and apparatus shall be adequate for operational and maintenance purposes and provision shall be made for escape in the event of fire. The escape route shall be designed to be clear of any obstructions. Passageways and the minimum spacing between equipment shall be provided in accordance with Appendix A: Fire Segregation at Primary and Grid Substations. Provision shall be made for entry of power, multicore, telephone and pilot cables, water supply and foul drainage pipes. Sufficient width and depth shall be available for the cable routes such that de-rating of the 11kV feeder cables is kept to a minimum. There shall be no mutual de-rating of outgoing feeder, Bus Interconnector or Transformer Incoming 11kV cables. Ducts from buildings shall normally extend a minimum distance of 500mm from the external face of the building. If the access road is immediately adjacent to the building, Version: 2



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then the ducts should be continued beneath the access road to facilitate cable installation. 5.3.2

Walls All brickwork and blockwork shall be of a high standard facing quality with bucket handle pointed joints externally and flush pointing internally, unless a match with existing brickwork pointing is required. Where possible all dimensions shall be in modular sizes to minimise cutting of bricks and blocks. Clay facing bricks 65mm thick shall be used externally and shall be a minimum strength of 50N/mm2 and a maximum water absorption of 7% when tested in accordance with the appropriate British Standard. All facing bricks used externally shall be F2 frost resistant designation. Internal walls shall be constructed to give a durable, low maintenance, dust free finish. Walls shall be painted with smooth masonry paint, magnolia colour. The final coat of paint is to be applied after installation of electrical equipment. All proposed bricks and blocks to be used are to be approved by the Company’s representative. Aerated concrete blocks are not acceptable for internal or external walls. Quoin blocks shall be used at cavity closures in blockwork. Cavity walls in substation buildings shall achieve a U value as required by the current issue of the Building Regulations for new buildings other than dwellings. All brickwork and blockwork shall be laid in mortar of appropriate strength for the location and exposure of the wall. Facing brickwork shall be used in the outer leaf below DPC level and shall extend at least 2 courses below finished ground level on all faces of the building. The type and colour of facing bricks used shall comply with Local Authority requirements. Bricks for use below ground shall be approved Class B uniform colour engineering bricks Wall ties shall be stainless steel. Solid walls of one brick thickness or greater to be cross bonded or tied together with stainless steel reinforcement or ties. Where expansion or contraction joints are incorporated they shall be constructed with Version: 2



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approved joint filler and finished with appropriate coloured sealant. Expansion joints shall be so positioned as to coincide with Brick/Block modular sizes to avoid unnecessary cutting. 5.3.3

Floors Floors of switch-houses will be of reinforced concrete power float finish and designed to withstand the weight of switchgear to be installed. The finished floor level will normally be a minimum of 150mm higher than the substation compound. Solid concrete floors shall incorporate a damp proof membrane. Floors shall be sealed against dust prior to installation of plant, and finished with light grey coloured floor paint. The final coat of paint is to be completed after installation of electrical equipment. Unistrut channels are to be set into the switchroom floor to provide fixings for the switchgear. Floors of control rooms may be of reinforced concrete, or removable floor panels supported on pedestals on a concrete sub-floor. Floor panels are to have an antistatic sheet vinyl finish. A suitable skirting shall be provided around the room perimeter. Concrete floors are to be finished as stated above. Where internal cable trenches are provided they shall be fitted with GRP or recycled plastic removable covers (with suitable lifting holes) on galvanised steel bearers or concrete walls. Covers shall have a non slip solid top surface. Covers shall be designed for easy removal and reinstatement, and shall be of manageable dimensions and weight. Trench designs shall incorporate suitable access arrangements including ladders, step irons and hand rails where appropriate. Where water ingress is considered possible, cable trenches within buildings shall be fitted with drainage gullies connected to the storm drainage system, or with a sump and automatic pump. All ducts passing into buildings shall be sealed to prevent ingress of water and vermin. Minimum depths of external ducts shall generally be 450mm for multicore cables and 750mm for power cables.

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There is no requirement to comply with the U value for floor elements, as stated in the Building Regulations, but floors shall be designed to be as ‘energy efficient’ as possible whilst accommodating the various cable entries required. 5.3.4

Windows and Ventilation Windows are not required for daylight conditions or ventilation in substation and shall not therefore be provided. Adequate mechanical ventilation shall be provided to the W.C. and Mess Room as required by Building Regulations. No natural or forced ventilation is required to other rooms.

5.3.5

Roofs Roofs can be a variety of different constructions including: •

Flat and constructed from pre-cast concrete beams overlaid with insulation board and/or lightweight screed laid to falls and covered with asphalt, or built up felt system.

•

Flat, with steel supporting structure and metal profile sheeting, finished with insulation and built up felt system.

•

Pitched, with concrete or clay tile finish on timber trusses or rafters. Ridge and edge details shall be of low maintenance proprietary design. Consideration shall be given to security aspects of pitched roofs, and these shall normally be used where the building is within the security boundary of the site.

•

Portal frame construction with steel profile sheet cladding.

•

System roof made up from proprietary system panels

Single ply membrane systems will not be accepted. For some of the above roof options a parapet or edge upstand will be required. Parapets should be of suitable structural design and may be 3 or 4 sided with a gutter or roof outlets as required. The roof design shall ensure efficient removal of rainwater and not create areas of ponding. The roof covering should be turned up the inside of the parapet/upstand and across the top to terminate in a suitable GRP trim. Coping stones will not be accepted. Version: 2



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Care must be taken to ensure that rainwater does not stand on top of the parapet and then run down the face of the brickwork through the joints in the GRP trim. Where fascia and soffit boards are provided, these shall be of low maintenance design (e.g. uPVC). The overall construction of the roof shall be such as to provide a minimum thermal insulation U value as required by the current issue of the Building Regulations for new buildings other than dwellings. Solar heat gain shall be limited by the use of suitable solar reflective finishes. Adequate means for the disposal of rainwater from the roof shall be made. Where possible, connections shall be made to the main surface water drain. The underside of pre-cast concrete roof units shall have a fair face finish. Units shall be manufactured with tolerances specified in the appropriate British Standard. Differences in soffit level of two adjacent units shall not exceed 6mm. The underside of pre-cast concrete roof units, or any other separate ceiling construction, shall be painted with matt white emulsion paint. Roofs shall be designed for occasional access and maintenance, snow and wind loading in accordance with the appropriate British Standard. 5.4

FENCING For full details of the fencing requirements see separate policy document: Specification for Fencing for Grid, Primary and Distribution Substations.

5.5

TRANSFORMER FOUNDATIONS AND BUND WALLS For full details of the design and construction of transformer foundations and bund walls see Appendix C: Transformer Foundations and Bund Walls.

5.6

EARTHWORKS/FOUNDATIONS Any earthworks shall be carried out in accordance with the Manual of Contract Documents for Highways Work: Volumes 1 and 2, as published by the Highways Agency. General site fill Version: 2



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material shall be imported graded granular material to the approval of the Company’s representative. All surplus spoil will be removed from site. An assessment of any imported fill material must be made to ensure it is compatible with the earthing requirements of the site. Suitable measures to mitigate unsuitable or contaminated ground conditions shall be adopted by the contractor. Measures may include removal or in situ treatment of the ground or containment. All such works shall be conducted in accordance with procedures approved by the relevant environmental authorities. Foundations and other below ground constructions shall be designed to resist chemical attack from ground contaminants. Excavations for foundations shall be taken down to such depths as to provide a solid foundation suitable for the loading to be applied. Foundations shall be taken down to sufficient depth to avoid being undermined by cable trench excavations. Foundations shall be of a type to suit the ground conditions and shall be designed such that long term differential settlement is kept within acceptable limits for operation of the electrical plant and apparatus. The total area of the substation compound must be suitable for access by a mobile elevated work platform. (MEWP) The existing subgrade must be assessed for MEWP access. A layer of suitable graded stone (MOT type 1 or 2) will be provided beneath the substation surfacing. The thickness of the stone layer will be designed to support the MEWP, but must be a minimum of 100mm. The Contractor will be responsible for any additional subgrade improvement that is required solely for construction use. 5.7

CONCRETE All structural concrete for work below ground level shall meet the requirements for sulphates as identified for each particular site. In addition suitable measures must be taken to avoid the risk of alkali-silica reaction. The minimum grade of structural concrete shall have a cube crushing strength of 35 N/mm2 at 28 days.

5.8

FORMWORK AND REINFORCEMENT All concrete surfaces except top surfaces shall be constructed using suitable formwork of a Version: 2



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quality and strength necessary to obtain true surfaces with a fair face. Where concrete is exposed at or above ground level, formed and unformed surfaces shall have the following grades of finish: All exposed items Type F3 finish Unseen surfaces Type F1 finish Top unformed surfaces Type U3, steel trowel finish All finishes are as specified in the Manual of Contract Documents for Highways Work: Volume 1, as published by the Highways Agency. Bases for steel or aluminium structures, transformers and other kiosks shall be set 75mm above finished compound level, and their edges finished with chamfers. Edges of bases and trenches cast flush with the compound level shall be finished with a bull-nosed trowel. Formwork ties will not be permitted to pass through oil bund walls or exposed structural concrete. 5.9

STEELWORK Any structural steelwork incorporated into the works shall receive appropriate surface preparation and be hot dip galvanised in accordance with BS EN ISO 1461. Likewise all associated fasteners, packings, etc. shall receive the same galvanised treatment.

5.10

EQUIPMENT SUPPORT STRUCTURES Support structure for plant and equipment including busbars shall be constructed from galvanised steel or aluminium. Structures shall be designed to accommodate all normal vertical and horizontal loads plus additional loadings associated with electrical fault conditions.

5.11

CABLE DUCTS / TRENCHES All cable ducts and trenches shall be designed to cater for specified future requirements and shall be of suitable construction to sustain all stated applied loadings. The preferred option is to direct lay all power and multicore cables with suitable ducts Version: 2



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beneath roads and other inaccessible areas. Ducts for power and multicore cables will generally be 125mm diameter and coloured black. On larger sites a cable duct and pit system may be used for multiicore cables. Alternatively an in situ or precast concrete trough solution is acceptable. Minimum depths of external ducts shall generally be 450mm for multicore cables and 750mm for power cables. When laying cable ducts the opportunity should be taken to lay additional spare ducts for potential future use. This is particularly advantageous beneath access roads or foundations. Covers of cable trenches/pits shall be so designed to carry the applied loadings and to be capable of being removed easily without a risk of compound chippings falling into the trench/trough. Also, when in place, lids shall not present a trip hazard. The preferred trench cover material is either GRP with a solid top surface or Recycled Plastic covers. In certain circumstances heavy duty trench covers may be necessary. (See separate specification document for details of trench covers). Trenches into buildings and compounds shall be designed so they cannot be used to gain unauthorised access into these areas. This may require the use of lockable covers. Bases of cable trenches shall be laid to falls and include suitable drainage provision. Where possible the drainage points shall be connected to the site surface water drainage system. 5.12

DRAINAGE For drainage requirements on Primary and Grid substation sites see Appendix B: Substation Drainage For drainage requirements associated with transformer bund walls see Appendix C: Transformer Foundations and Bund Walls Suitable waste pipes and drainage gullies shall be provided to take away the condensate from dehumidification equipment. Surface water and foul drainage systems shall comply with the requirements of the appropriate statutory authorities. Discharge into water courses or into the any existing drainage systems will not be permitted without written consent of the appropriate Version: 2



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statutory authorities, which shall be obtained prior to commencement of the works. The design of the drainage systems must take into account the loadings which may be applied from heavy vehicles such as transformer delivery vehicles, or the use of MEWPs in compound areas.

5.13

SITE SURFACING All newly developed or re-developed areas of substation compound shall be stripped of all topsoil and vegetation. The finished area of the substation compound shall be resurfaced with a low maintenance finish suitable for easy access for maintenance of equipment. This layer will also act as an electrical insulator to minimise touch and step potentials during electrical fault conditions. This finish will be a 75mm thickness of 20mm single size granite, basalt or carboniferous limestone chippings laid on geotextile material conforming to clause 609 of the Specification for Highway Works (SHW), Volume 1 of the Highways Agency’s Manual of Contract Documents for Highway Works. Other similar types of chippings may be suitable subject to approval by the Company. The chipping layer must extend a minimum of 1.5 metres outside the line of the compound fence. Site surfacing and geotextile material shall not be laid until after installation of all cables and electrical equipment. It is the Contractor’s responsibility to protect the formation prior to laying of the geotextile material and surfacing Areas outside the compound but within the boundary fence shall generally be finished in accordance with the compound requirements above. However on some sites there may be a planning requirement for landscaping which will replace some of the stone chipped areas. All landscaping shall be designed to avoid future problems with overhead lines, buried services, etc. and must have minimum maintenance requirements.

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5.14

ROADS AND PATHS Site roads which may be used for the moving of heavy items of plant should normally be designed to cater for transformer delivery vehicles. It is essential to ensure that all cable ducts and other services which are to be laid under substation roads are in position before construction of the road commences. Roads shall be designed to suitable horizontal and vertical alignments to meet the requirements in the Site Layout section above. In particular vertical alignments shall avoid sharp gradient transitions. Within compounds gradients shall kept to a minimum and will usually be determined by drainage requirements. Roads shall generally have upstand kerbs to direct water flows, and to contain any oil spillage within the drainage system The roads shall preferably be of dense bitumen macadam or hot rolled asphalt construction. Thickness of base and wearing course materials shall be calculated from design loads but shall be a minimum of 60mm and 30mm respectively. For substation buildings suitable concrete access paths shall be provided for access to normal entry doors and doors designated for delivery of plant. Other doors should have a simple concrete pad outside the door. All paths and pads shall have a non slip finish and should direct any rainwater away from the building.

5.15

NOISE HOUSINGS

5.15.1 Design Noise housings shall be constructed from proprietary ‘sandwich’ panels consisting of an inner and outer metal sheet with sound absorbing filler material. The proposed design shall have appropriate fire resistance as stated in Appendix A: Fire Segregation at Primary and Grid Substations and shall be approved by the Company’s representative prior to fabrication. The required insertion loss to be provided by each enclosure shall be agreed between the Company and the manufacturer following the necessary site noise survey. The enclosures shall be designed and constructed as to allow sufficient room for access for maintenance on the transformer and its ancillaries. Where power or multicore cable runs Version: 2



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restrict pedestrian routes inside housings, suitable galvanised steel internal walkways and steps shall be designed and fitted to provide safe access. The enclosure shall be designed to withstand all superimposed and wind loads, including maintenance access loading for the roof construction. Provision shall be made for the collection of rainwater and its disposal into the bunded area. A suitable foam inlet for fire fighting purposes shall be provided to the housing. Vermin proof grilles shall be provided to apertures between housing and cooler areas. The position of enclosure walls shall be determined using the minimum requirements in Appendix A: ‘Fire Segregation at Primary and Grid Substations, and in Appendix C: Transformer Foundations and Bund Walls. Two steel lockable access doors shall be provided with each enclosure at diametrically opposite corners with appropriate fire resistance to match that of the housing (generally 2 or 4 hours). The doors shall give a clear opening 2000mm high by 750mm wide. Doors shall close on to resilient seals along all meeting faces. Doors shall be fitted with: • Push bar panic latch with external LEVER type lockable handle incorporating europrofile cylinder • Garage type hold open stay • Emergency exit signage as appropriate. Concrete or steel steps shall be provided to allow safe access/egress to the housing over the bund wall. Externally a minimum 900mm square platform shall be provided with steps and handrails. 5.15.2 Construction For the protection of transformer paintwork, it is a requirement that enclosure roofs shall be waterproofed and that all seals around pipe work and turrets are water tight. Proprietary metal sandwich panel construction housings shall have panels bolted together Version: 2



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using a suitable resilient gasket materials to form a watertight seal. All components shall be galvanised after fabrication. In some instances a coloured paint finish may be required on top of the galvanising to meet planning requirements. No site drilling or welding of the housing components will be permitted.

5.16

SECURITY

All sites shall be risk assessed to determine what security measures are appropriate. The minimum requirement for all sites is to have an intruder alarm which covers the building and the compound access gates. The risk assessment will determine what type of boundary fencing is appropriate, subject to planning agreement, and also if further measures such as electric fences to compounds or close circuit television systems are required. Specifications for intruder alarms and CCTV systems are provided by the E.ON UK Security Technical Installations Manager. Substation buildings shall be located, where possible, so they are either inside or outside a security palisade fence, depending on security risk assessment. If due to lack of space a substation building forms part of a security perimeter of a site, then additional measures should be considered to ensure adequate protection. In particular walls shall be ‘smooth faced’ without climbing aids, and rainwater pipes shall be positioned inside the security perimeter, or protected by anti climb measures to prevent unauthorised access. Measures must also be taken to prevent theft of earth tape. Any exposed earth tape must be capped in accordance with the requirements stated in the Earthing Manual. 5.17

FIRE PROTECTION Sites must be individually fire risk assessed to determine what fire prevention and fire fighting measures are appropriate. For relatively simple layout sites with single storey buildings then the following minimum requirements will usually be adequate: Version: 2



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All buildings shall be fitted with smoke detectors to switchrooms and control rooms.

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All buildings shall be fitted with a minimum of one fire fighting point, usually situated immediately inside the control room door. The fire point will consist of one dry powder extinguisher and one carbon dioxide extinguisher, together with appropriate labels. Central Networks will supply and install the fire extinguishers.

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A fire action notice will be provided adjacent to the telephone point.

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All fire exit routes and final exit doors will be marked with appropriate standard fire exit signage.

For more complex sites additional fire prevention and fire fighting equipment may be required, dependant on the fire risk assessment. For further details see the separate policy document: Fire and Bomb Safety at Operational Sites. 5.18

DOORS For full details see Appendix D: Doors for Primary and Grid Substations

5.19

HEATING AND LIGHTING Design and installation of heating and lighting systems, including LV power systems, is detailed in Appendix E: Heating, Lighting and Small Power at Primary and Grid Substations. This document also includes information on floodlighting for substations, intruder alarms and other associated electrical items.

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Civil Design and Construction of 132kv 66kV and 33kV Substation

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