This paper investigates coolant topologies for High Temperature Superconducting (HTS) transmission and distribution cable systems. We explore options that allow for flexibility of operation, low temperature rise in the superconductor and low refrigerator power consumption. Topologies for cooling the cryostat and HTS in long-distance electric power transmission systems are explored. For transmission, the goal is to achieve long spans between cooling stations along the transmission line, and low power consumption. For HTS distribution systems, the issue is cooling the superconductor and the current leads and the goals are to minimize the power consumption and to prevent excessive heating of the superconductor. Means are explored to cool distribution systems where cryogenic loads are dominated by current lead loss. Use of multiple fluids or multiple coolant circuits of the same fluid to decrease the energy ingress in the low temperature environment is described. Potential alternative coolants are proposed. We show that it is possible to reduce electrical consumption by about a factor of 2, while also decreasing the temperature rise of the superconductor
