A thermal constraint study of the Wellington regional transmission network

The 2010 Annual Planning Report (APR) of Transpower New Zealand, the owner and operator of the New Zealand (NZ) grid, has indicated a capacity issue in the Wellington 110 kV load area particularly after standing down the inter-island HVDC Pole 1 in late 2007. Presently, the HVDC link is coupled with the Wellington 220 kV AC network, and thus the capacity into the 110 kV load area is dependent on the HVDC transfer level and its direction. This paper presents a study carried out to identify this capacity issue, and to investigate the preferred corrective measure. The analysis covers the system under normal conditions, and under various contingency situations.