Underground DC Cable Sizing with Cyclical Loading in Utility-Scale Solar Applications

In utility-scale photovoltaic (PV) plants, the extensive DC wiring required constitutes a significant portion of the overall system cost. It is therefore important to ensure that DC cable sizing is optimized for project economics while meeting all electrical safety requirements. Ampacity studies are carried out to determine the required conductor sizes and arrangements, by assessing whether each cable will operate within its insulation temperature rating under the given installation and operation conditions. This paper presents the methodology applied to specify the underground DC cables for a 32 MW PV plant in New Zealand. A cable thermal analysis is carried out in the ETAP software under different steady-state and transient scenarios to demonstrate that a cost escalation of 46% in DC conductors can be avoided by considering the intermittent nature of the PV load in the project’s ampacity study.