Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

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Vantage to Pomona Heights Chapter 2 230 kV Transmission Line Project FEIS Proposed Action and Alternatives PAGE 2-43 Trenching, conduit installation, and backfilling would proceed progressively along the route such that relatively short sections of trench (typically 200 feet per crew) would be open at any given time and location. Splice Vault Installation At intervals of approximately 1,500 to 2,000 feet along the route, pre-cast concrete splice vaults would be installed below ground. The length of an underground cable section between splice vaults and, therefore, the locations of the splice vaults are determined based on engineering requirements and land constraints. Engineering requirements include: the maximum allowable cable pulling tensions; maximum allowable cable sidewall pressure; and cable weight/length that can fit on a reel and be safely shipped. The specific locations of splice vaults would be determined during final engineering design. Figure 2-9 shows typical underground splice vault installation (duel vaults). For safety purposes, the splice vault excavation would be shored and fenced. Each vault would have two entry points to the surface. After backfilling, these entry points would be identifiable as manhole covers, which would be set flush with the ground. Conduit Testing After the vaults and duct bank are in place, the conduits would be swabbed and tested (proofed) using an internal inspection device (mandrel) to check for defects. Mandrelling is a testing procedure in which a “pig” (a painted aluminum or wood cylindrical object that is slightly smaller in diameter than the conduit) is pulled through the conduit. This is done to ensure that the “pig” can pass easily, verifying that the conduit has not been crushed, damaged, or installed improperly. Cable Installation After successful proofing, the transmission cables and ground continuity conductors would be installed and spliced. Cable reels would be delivered by tractor trailers to the vault sites, where the cable would be pulled into the conduit using a truck-mounted winch and cable handling equipment. To install each transmission cable and ground continuity conductor within the conduits, the large cable reel would be set up over the splice vault and a winch would be set up at one of the adjacent splice vault locations. The cables and the ground continuity conductors (during a separate mobilization) would then be inserted in the conduits by winching a pull rope attached to the ends of each cable. The splice vaults would also be used as pull points for installing the temperature sensing fiber optic cables under a separate pulling operation. In addition, pull boxes would be installed near the splice vaults for the pulling and splicing operations required for the remaining fiber optic cables. Cable Splicing After the transmission cables and ground continuity conductors are pulled into their respective conduits, the ends would be spliced together in the vaults. Because of the time-consuming precise nature of splicing high -voltage transmission cables, the sensitivity of the cables to moisture (moisture is detrimental to the life of the cable), and the need to maintain a clean working environment, splicing XLPE cables involves a complex procedure that requires a controlled atmosphere. This “clean room” atmosphere would be provided by an enclosure or vehicle that must be located over the manhole access points during the splicing process. It is expected to take approximately five to seven days to complete the splices in each splice vault. Each cable and associated splice would be stacked vertically and supported on the wall of the splice vault via a racking system. During commissioning, access to splice vaults may be required. Underground to Overhead Transition Stations High voltage underground transmission lines require transition stations whenever the underground cable connects to overhead transmission. The appearance of a transition station is similar to that of a small switching station. The size is governed by whether reactors or other similar components are required.