For the Thumb Loop 345 kV transmission line project, MCTransmission (ITC) chose to evaluate the feasibility of modifying existing single-circuit 765 kV lattice steel towers for a double-circuit 345 kV application. In order to establish the feasibility of converting the single-circuit 765 kV structure to double-circuit 345 kV, structural and electrical evaluations were performed. Structural analysis using current ITC loading criteria indicated that the structural capacity of the towers would be sufficient and that no structural modifications would be required. Electrical analysis of clearances, lightning protection, insulation coordination, and electromagnetic field (EMF) performance indicated that electrically, the existing single-circuit 765 kV lattice steel towers could be modified to function adequately in a double-circuit 345 kV application. Furthermore, the existing single-circuit quad-bundle conductor could be reconfigured in a double-circuit twin-bundle configuration.
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