The outdoor equipment in switchyard are supported on steel structures. The steel structure works in outdoor switchyard are, fabrication and erection of towers, girders and supporting structure for equipment. The fabricated structures are galvanized to prevent structural corrosion at site. The fabricated structures are erected over the foundation already casted prior to the installation of equipment and conductors. The various steel structures in substation are gantry structure, outgoing feeder, equipment support structure, cable support, station transformers. Gantry structure and outgoing feeder can be made up of either rolled steel joist or lattice structure. The equipment support structures can be provided with rolled steel joists or lattice or pipe structures. The cables and station transformers are supported on a double pole structure made up of either rolled steel joist or pre-stressed concrete. The two figures shown here are differentiating the substitution structures provided with rolled steel joist and lattice members. Let us know in brief about the tower and girder. Tower, is the lattice tall structure to support gantry and shield wire. Girder is the lattice horizontal structure to support conductor. The figure presents a typical assembly first, which are tower and girder. The configuration to be adapted for a tower and girder depends on the factors like face-to-face or conductor to conductor clearance, conductor to tower clearance or sectional clearance or air clearance. Ground wire clearance from topmost conductor. Mid span clearance of conductors based on its dynamic behavior, that is sag. Minimum clearance of lowermost conductor above ground level are from equipment bus level. The electrical clearance, geometry of the tower and the level at which the gantry is to be supported will decide the height of the tower structure, as evidenced from the table. Therefore the factors which governs the tower height are minimum permissible ground clearance, maximum sag, vertical spacing between conductors, that is girder to girder spacing, vertical spacing between ground wire and top of conductor. While designing the tower and girder structures, the following parameters needs to be considered: transmission voltage, that is fault level, number of circuits provided , prevailing climatic conditions, conductor and hardware, that is: corona, spacer, etc, earth wire, located at tower peak. Insulators and hardware, either tension or suspension, and the span, increase in span causes increase in conductor weight, resulting into increased normal conductor tension and short-circuit force. This slide, we'll talk about the equipment input record from vendor for partial in structural engineering. For minor equipment like post translator, surge arrestor, current transformer, potential transformer, and horn gap fuse. The details of equipment based mounting on structure is required. Coming to the major equipment, these are basically isolators or air break switch, vacuum circuit breaker and transformers of all ratings. For isolator, or air break switch details like the location of operating pipe, its operating mechanism, and earth switch box fixing locations need to be known. For vacuum circuit breaker, the foundation bolt arrangement details is to be provided. If there is any ladder present, the fixing location need to be known. For transformers, base mounting, and jack pad details along with the center to center distance between rails will be appreciable. Apart from the major and minor equipment, few critical equipment such as distribution transformer, ring main unit, feeder pillar and capacitor bank are also there in substitution. For distribution transformer inputs in the form of base mounting details and cut out for cable opening requirement are provided. For ring main unit and feeder pillar, vendor input includes the cable gland location and details of equipment mounting arrangement. For capacitor bank, the base fixing details and arrangement details for tertiary equipments like isolator and post insulator are supposed to be with structural engineering team as vendor input. This picture shows an actual view of equipment support structure. The major components of equipment support structures are as follows: Equipment bus bar, this can be either tubular or flexible. Equipment itself, the details for which are to be obtained from vendor drawing. Clumps and connectors, earth flat, operating box or junction box. Last but not the least, is the support structure and its foundation. This slide will brief about the salient features of the foundation for steel supporting structures, and the associated requirements. Foundation drawings of towers and equipment support structures are made after concluding the outdoor switchyard layout , and structured design. Location and orientation will be with respect to the foundation layout as shown in the figure. The number of structure or foundation shall be as per layout arrangement. Base plan arrangement, and foundation bolt location details shall be verified with structural drawings prior to erection of bolt. Wherever the foundations with the different depths are present in close vicinity, the construction of the deeper foundation shall commence first. The plinth level of the pedestal of foundation and the alignment of foundation bolt for the steel support structure are crucial and hence their construction shall be strictly as per the drawings. The steel structures are erected on top of foundation and after getting clearance from concern engineer, the structural base plate is grouted with the cementitious grout. It is to be ensured that the foundations are not falling with the underground systems. Construction of road falls under the major infrastructure works in substitution project. Roads are provided for access to the equipment during erection and maintenance. In general, there are three types of road that can be provided in substation. These are roads with flexible payment made up of asphalt with black surface appearance as shown in figure. Road, with the rigid pavement made up of reinforce cement concrete, which appears like gray surface as shown in figure. The third type is earthen road or waterborne macadam roads. Footpaths may also be provided alongside of these roads. Roads shall be provided from entrance up to control building and also for access to transformer. In case of level difference road shall be laid in slope of 1 vertical to 12 horizontal with the proper side embarkment for easy movement of vehicles. The figure represents the layout of substation with the road arrangement which source that proper turning radius shall be provided at turning locations. The civil underground system comprises three major constructions. Namely; cabled trench, storm water drain, duct banks and culverts. Once the substation building under the switch yard equipment layouts are finalized based on the electrical cable routing prepared by electrical engineer, cable trenches are constructed to route the cables. Cables are rooted normally in body retrench, concrete trench, and in plastic, polyvinyl chloride duck banks in accordance with local practice. The cable trench shall not be used as storm water drain. Storm water drain shall be constructed to drain out the surface runoff that discharge or outfall for these drains shall be at the lowest point of land to avoid back flooding in substation premises. Duct banks are the structures consisting pipes in [inaudible] PCC. Duct bank is provided where the cables are crossing a road and or a drain or a project specific area. Culverts are provided for our drains as a road crossing which shall be designed for vehicular load of class AA traffic as per IRC provisions. The construction drawings are released to align with the following construction sequence of the underground system. Construction of foundation will commence first. After the completion of foundation, the cable trench will be constructed, followed by storm water drains. At last, the duct banks and culverts will be constructed. The other underground systems are designed as per civil engineering procedures. Precast techniques shall be used in few of underground system as per construction requirement. Completing all civil work below ground is a major milestone that helps complete whole project
