- PURPOSE
1.1 This engineering standard establishes the design requirements for transformer foundations designed for Company installations.
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Electrical Transformer Foundations Details
2.1 This standard applies to foundations for oil-filled, outdoor transformers designed by Company Europe, for installation in the UK or Europe. Transformers installed in other locations may be subject to different requirements.
- RELATED DOCUMENTS
Note: Design shall be according to this document and those listed below.
3.1 Engineering Documents
Fire Protection Systems
- FOUNDATIONS FOR U.K. AND EUROPEAN INSTALLATIONS
4.1 The foundation design shall be according to the following:
4.1.1 Small Transformers for UK installations: Small transformers shall be defined as those with an oil capacity of 2 m3 or less, and the foundation design will depend on the water table as follows:
4.1.1.1 When the water table is more than 1 m below grade level, the foundation shall comprise of a rectangular concrete plinth, dimensioned to accept the wheels or base of the transformer, and having a height of at least 150 mm above grade level. The surrounding ground over a plan area of 10 m2 shall be excavated to a depth of 0.5 m and replaced with pebbles.
4.1.1.2 When the water table is less than 1.0 m below grade level, a concrete pit shall be required to contain the plinth. The pit shall be drained to the surface water drain through a small penstock, which is normally kept closed. The top of the pit wall shall be level with the top of the plinth, and the pit is filled with pebbles, to grade level.
4.1.2 Small Transformers for European installations: These shall be designed according to paragraph 4.1.3 for large transformers.
4.1.3 Large Transformers: Large transformers shall be defined as those with an oil capacity greater than 2 m3 and the foundation design shall be as follows:
4.1.3.1 A concrete pit shall be required containing either internal cross walls or a plinth to support the transformer. The bottom of the pit is laid to falls and drains to a sump with a steel cover plate and suction pipe to enable drainage of the compound.
4.1.3.2 A galvanised steel open grid screen shall be located over the open pit and shall be covered with a pebble layer of 200 mm thickness. The top of the pebble layer shall be level with the top of the transformer plinth. The void volume of the pit below the screen shall be sized to accommodate the volume of the oil in the transformer. When more than one transformer is located within the pit area, the volume of oil of the largest transformer shall be assumed for the sizing of the pit.
- TECHNICAL DETAILS
5.1 The pebble gauge shall be 40 to 60 mm.
5.2 The void ratio shall be taken as 40% and the total void volume must not be less than the volume of transformer oil.
5.3 The pit dimensions must exceed the overall transformer dimensions.
5.4 Cable ducts within the pit should normally be steel, except that ducts containing cables on the low tension (LT) side must be of nonmetallic material. Ducts entirely encased by concrete may be stone ware or polyvinyl chloride (PVC).
5.5 Drainage shall be arranged so that oil cannot enter surface water drains.
5.6 Installation of transformers shall be considered in the design and allowance for rails. Channel bearers or pulling posts shall be assessed.
- TRANSFORMER COMPOUND
6.1 When more than one transformer is located within a compound, the electrical engineer shall determine whether separation walls are required.
6.2 The compound shall be enclosed by a fence according to Fences and Gates. The fence shall have lockable gates to enable the withdrawal and installation of each transformer. A minimum of one lockable personnel access gate shall be provided within the compound fence. All gates shall carry notices of high voltage (HV) hazards.
6.3 When a transformer compound is located adjacent to a switch house or other building, the side of the switch house or building facing the transformer compound shall be of brick construction or other fire-rated material, and shall not contain doors, windows, or similar openings.
6.4 The electrical engineer shall decide if fire and/or blast walls are required, and shall specify their position and height. All blast walls shall be designed to appropriate codes and standards.
6.5 There shall be a clear passage at least 600 mm wide between the transformer and surrounding wall or fence.
6.6 The ground within the compound (i.e., outside the pit), shall be covered with a 65 mm layer of chippings, and kept free of weeds, according to Footpaths and Landscaping.