While heavy equipment such as transformers, reactors, etc are mounted directly on foundation and other equipment like surgery, stirs, isolators, circuit breakers etc, requiring electrical clearances to ground are mounted on support structure. All support structures in turn are mounted on respective foundations, transformer foundation, outdoor steel structures and infrastructure works. This topic describes transformer foundation, fire wall, fire rated doors, steel structure for tower, gantry and equipment support. Infrastructure works such as road, drain, fence and compound wall. The transformer maybe skid mounted or wheel mounted. The transformer manufacturer will provide a foundation plan for the transformer indicating the footprint for the skid or wheel base. Location of will our skid and dimensions of the jacking pads. Block foundation or pedestal foundation is provided to the extent such that all load bearing members such as the skid are reels and jacking pads are seated firmly and properly. Always for minor site variations shall be provisioned on such dimensions. Around the foundation, oil collection pit shall be provided to collect oil that may leak or drain from transformer. Foundation size shall also be coordinated with the trenches and cable boxes provided on the transformer to enable all power and control cables from trenches are properly terminated without violating the radius of cable bending etc. Rails on transformer foundation are provided to facilitate the erection and maintenance of transformers. Where the transformer is provided with wheels, rails shall be embedded on the foundation to seat transformer wheels properly. There shall be locking provisions for the wheels on the rails. The rails shall extend up to the road so that transformer can be marshaled or wheeled on rails in case of any major maintenance activity. The hazard of fire spreading from one large transformer to another is prevented or mitigated by providing fire wall. The type and thickness of fire wall is based on the fire rating stipulated by the local regulations. Typically in India it is two hours. The hazard of fire spreading from one panel room to another in the same building is mitigated by having steel doors of fire rating of three hours. In the Middle East where ambient temperature is very high, transformers are located beside the substation building with all four sides and roof covered. The sides without fire wall are covered by lured panels to facilitate free air circulation. The sheet steel roof will provide the required shade. Oil collection pit around transformer. Transformer with the oil capacity of more than 5000 liters shall be provided with oil collection pit around the transformer foundation to collect oil that may leak or drain from the transformer. Oil soak pit shall be filled with suitable gravels with wides of capacity adequate to contain the oil volume of the transformer. The volume of soak pit shall be such to hold complete oil of the transformer and 10 minutes of fire water. If gravel filling is used in the soak pit, only the volume of available void shall be considered for this purpose. In India, as per CEA, Central Electricity Authority 2010, Part B. Substations 33 by 11 kV, 33 by 22 kV and 22 by 11 kV. The oil collection pit is not required for the transformers of primary voltage up to 33 kV. Common oil collection tank. If a separate oil collection tank is provided, it is sufficient to have soak pit below the transformer designed for one third of the transformer oil volume. The capacity of common oil collection tank shall be to hold the oil volume of the largest transformer and 10 minutes of fire water. IS:1646 provides recommendations for provision of fire wall in substation. Fire wall shall be provided wherever oil capacity of individual transformer is between 5000 to 20,000 liters and if clear space is less than eight metres between the transformers. Fire wall shall also be provided wherever oil capacity of individual transformer is more than 20,000 litres and if clear space is less than 15 meters between the transformers. The building wall shall be provided as a fire wall when transformer is placed within six meters from the building. The bus conductors and conductors from transmission tower are supported on the girder and tower supports the girder. The outdoor equipment in switchyard are supported on steel structure. Electrical clearance will decide the height of the structure, the level at which the gantry is to be supported and the geometry of the tower. Tower is the latest tall structure to support gantry and shield wire instead of lattice structures, rolled steel joist or RSJ sections are also usually adopted. Girder is the lattice horizontal structure to support conductor. Equipment supporting structure, lattice short structure to support outdoor switchyard equipment like CTPT, isolator, circuit breakers, etc. It is also normal practice to provide galvanized steel pipe support for outdoor equipment instead of lattice type of supports. Foundation boat, these structures are connected with foundation by using anchor or foundation bolts. Infrastructure work comprises substation roads, gravel filling, storm water drain, fence and compound wall. Roads are provided for access to the equipment during erection and maintenance. Roads shall be concrete or asphalt or paving. The width of the roads will be 3.75 meters minimum and depends on the movement of size of vehicle that carry the equipment. Approach road slope shall be suitable for smooth access to vehicles. Drains, the surface drain of rainwater is to be planned in such a way that no part of the switchyard is inundated during rain and shall be taken care during grading of the plot. Rainwater should also get drained from the area of gravel stone spread provided to avoid any weed or vegetation growth. Gravel filling, reasons for providing stone spreading in substations. The stone layer on the substation ground provides high resistance so that the fault currents flow into the ground but not along the ground. Stone layer also minimizes step and touch potential. Fence and compound wall. The entire substation including switchyard and all buildings is a restricted area and hence it shall be secured by a chain link fence or compound wall of 2.5 meters high. Barbed wire coil at the top is additionally provided wherever it is needed. An additional fence of two meters height within the switchyard boundary shall be provided without barbed wire on the top. To separate the switchyard area from the building area, to restrict unauthorized access into the switchyard. At the locations wherever adequate clearances could not be maintained from live conductors, access to such areas shall be restricted. The main gate of 4 to 5 meters width along with 1.25 meters wide. Personnel wicket gate shall be provided at entry of the switchyard, interdisciplinary interfaces. Most of the civil facilities are constructed based on electrical requirements. Hence electrical engineer and concerned civil engineer shall closely coordinate and finalize design interfaces. Most of the mechanical facilities also require civil interfaces like trench works for water lines, support arrangement for firefighting lines, foundation or pedestal for HVAC equipment etc. Here is a quick recap of what you have learned thus far, the transformer maybe skid mounted or wheel mounted. Pedestal foundation or block foundation is provided to the extent such that all load-bearing members are seated firmly and properly. The hazard of fire spreading from one large transformer to another is prevented or mitigated by providing fire wall. Firewall shall be provided wherever oil capacity of individual transformer is more than 20,000 litres and clear space between transformer is less than 15 meters. Also, if the oil capacity of individual transformer is between 5000 to 20,000 litres and clear space between them is Less than eight metres, a fire wall shall be provided. Building walls shall be provided as fire wall when transformer is placed within six metres from building. Transformer with oil capacity of more than 5000 litres shall be provided with oil collection pit around the transformer foundation to collect oil that may leak or drain from the transformer. The bus conductors and conductors from transmission tower are supported on girder and tower supports the girder. The outdoor equipment in switchyard are supported on steel structure. Electrical clearance will decide the height of the structure, the level at which the gantry is to be supported and the geometry tower. Infrastructure work comprise of substation roads, gravel filling, stormwater drain, fence and compound wall. Electrical, civil and mechanical engineers shall closely coordinate and finalize design interfaces.
