Ampacity evaluation of high-pressure gas-filled- (HPGF) pipe-type cables under Bridgeport harbor

Ampacities of two 115 kV high-pressure gas-filled (HPGF) pipe-type cables in Bridgeport, Connecticut are limited by a portion of the circuit that crosses under the Pequonnock river. The installation conditions, soil thermal parameters and circuit loading effects were studied using various technologies including a gyroscopic route survey, hydrographic water bottom evaluation to find the depth of cover, and temperature measurements with thermocouples and distributed temperature sensing (DTS) using fiber optic cable. The results of the evaluation showed that the loss factors were increasing on the circuits and the ratio of one circuit´s load to the other was becoming smaller, both of which resulted in a reduction in the peak current carrying capacity. However, additional studies were able to reveal several methods for uprating the circuit capacity including the use of forced air ventilation on a spare pipe running in parallel with the two energized cable pipes. This paper summarizes the results of ampacity study and describes the various uprating techniques that were applied.