The existing HVDC scheme connecting the North Island and the South Island of New Zealand is presently being upgraded to 1400 MW. As part of the HVDC upgrade, a time domain simulation model of the interconnector is developed and presented in this paper. The model will be used to study transient stability and the dynamic performance of the HVDC link and both interconnected power systems. Special features of the model are several power modulation controllers designed for frequency and voltage support and the utilization of a round power operation mode.