Roads, trenches and buildings

The civil works of a substation are the roads, the fence, the buildings, the transformer pits and firewalls, and the surface layer of gravel. The design places them with the yard layout (Yard layout) and lists their quantities in the Civil section of the bill of materials (BOM). This topic gives the rules that size them and the quantities of the default 220 kV project.

Read first: Yard layout

1RoadsCopy link to Roads

The design generates the internal road, the ICT road and the peripheral road, aligned with the buses. The internal road, 4 m wide, runs between the high-voltage (HV) transformer bays and the transformers. The interconnecting transformer (ICT) road, 7 m wide, runs between the transformer row and the control building. It is the access of the transformer trailer, and the plan labels it so.

Both roads run along the length of the buses. Where the transformer row is spread beyond the bus ends, they run on to the tank at the end of the row. The peripheral road, 4 m wide, runs round the structures, its inner edge 2 m outside the outermost structure: the HV yard, the transformer pits, the building, an outdoor MV yard and the fenced reactive power area.

The roads can be changed by layout edits. The internal and ICT roads move north or south and take a width, and the peripheral road takes a width. A road's width is at least the design's and at most 50 m. A road can also be added, from the fence's south side to the control building, with lengths of at least the internal road's width and at most 1000 m. An added road stays inside the fence and clear of the equipment, the transformers, the building and the areas, and it may join or cross another road.

The BOM's road line is the area of the peripheral road's ring, the internal road, the ICT road and the added roads. In the IEC + CEA / CBIP set it reads water-bound macadam (WBM) or bituminous roads, and in the ANSI / IEEE set an aggregate base with asphalt.

2Fence and gateCopy link to Fence and gate

The fence stands 3 m beyond the peripheral road's outer edge, round the whole site. The CEA Safety Regulations 2023 require an outdoor substation to be fenced to a height of not less than 1.8 m, and the fencing to be earthed (Reg. 51(ii)(a)). The IEC + CEA / CBIP set's fence is a chain-link fence 2.4 m high. The ANSI / IEEE set's is 2.44 m high, the 8 ft of fabric and barbed wire that RUS Bulletin 1724E-300 recommends.

The earth mat's outer conductor runs 1.5 m outside the fence, and the fence is bonded to the mat. The fence has a gate of 6 m, which the 3D model shows as a sliding gate on the south side. The BOM's fence line is the fence's perimeter.

The live parts of the HV yard stand at least 9 m inside the fence: the gap to the peripheral road, the road's width and the fence offset. The ANSI / IEEE set checks the road's width and the fence offset, 7 m, against the safety clearance zone R of NESC 2007 Rule 110A. It checks the height of the line conductors that cross the fence against R too. A layout edit can move a side of the fence out or in. A side less than the fence offset beyond the peripheral road fails the fence items of the compliance checklist.

3Control buildingCopy link to Control building

The control building stands 3 m south of the ICT road, on the plant side, and is 12 m deep. Its rooms run from west to east in this order:

1. the MV switchgear hall, with indoor medium-voltage (MV) switchgear
2. the control and relay room, 15 m long
3. the battery and charger room, 6 m long
4. the storage and toilet room, 6 m long

The switchgear hall is 1.0 m long per panel, with an end aisle of 2 m at each end. With an outdoor MV yard there is no hall: the MV yard stands west of the building, and a gap of 4 m separates the two. A switching substation has no MV switchgear, so its building has the other rooms only. It stands east of the lower HV yard, clear of the lines that leave south.

A layout edit can move the building, turn it in steps of 90°, and lengthen its rooms or deepen it, never below the design's sizes. The station service loads read the building: the lighting from its area, the air conditioning from the control and relay room and the battery room, and the ventilation from the switchgear hall. The BOM's building line is the building's floor area, in reinforced cement concrete (RCC) in the IEC + CEA / CBIP set and reinforced concrete in the ANSI / IEEE set.

4Transformer pits and firewallsCopy link to Transformer pits and firewalls

Each transformer and bus reactor stands in a soak pit that extends 1.5 m beyond its tank, filled with gravel. The soak pits drain to a common burnt-oil pit, 5 m square, in a column of the transformer row that has no transformer (Yard layout, The transformer row). A firewall 0.3 m thick, extending 0.6 m beyond the tanks, stands between transformers side by side whose clear gap is below 10 m.

The CEA Safety Regulations 2023 require separation or fire barrier walls between oil-filled apparatus holding more than 2000 l of oil, and a suitable oil soak pit for such apparatus (Reg. 46(2)(vii)). The same regulation requires a drain-away for more than 9000 l in one tank. The regulation sets these by the oil quantity. The firewall's clear gap of 10 m is the design's.

The design places the pits and gives their plan size. It does not calculate the pits' volume or their construction. The compliance checklist of the ANSI / IEEE set asks for these to be answered from the civil design, against IEEE 980.

5Gravel, reactive power area and GIS hallCopy link to Gravel, reactive power area and GIS hall

The surface layer of gravel covers the earth mat's area, and the BOM's gravel line is that area times the layer's depth. The layer's resistivity and depth are the inputs Gravel resistivity and Gravel depth, which also set the tolerable touch and step voltages (Surface layer and Cs).

The static var generator (SVG) area and the harmonic filters stand inside a fence of their own, 2 m outside them. The SVG area takes 6.4 m² per MVAr at a depth of 10 m, and a filter 15 m per MV section.

A gas-insulated switchgear (GIS) yard adds its hall to the Civil section, a concrete frame with cladding counted by its floor area, and the electric overhead travelling (EOT) crane of the hall.

6Cable trenches, foundations and drainageCopy link to Cable trenches, foundations and drainage

The generated layout has no cable trench routes, no equipment foundations and no site drainage network, and the BOM's Civil section has no lines for them. The 3D model shows the equipment on its supports, without foundations. The Sketch library of the yard sheet has a cable trench footprint, which draws a trench on the sheet and does not enter the quantities.