Annual Planning Report 2012 - Transpower

Chapter 6: Grid BackboneThe North Auckland and Northland (NAaN) project that increases thetransmission capacity in the Auckland and Northland regions (see Chapter 7,Section 7.8.4 for more information).The North Island Grid Upgrade (NIGU) project that increases the transmissioncapacity into the Auckland and Northland regions (see Section 6.4.2 for moreinformation).Even with these approved projects, voltage stability will be an ongoing issue.Resolving projectsWe have commenced an investigation to determine the amount of additional reactivesupport required to relieve the Upper North Island voltage stability issue beyond thecompletion of the NAaN and NIGU projects.Additional reactive support will be required about every two-three years. This will bea mixture of capacitors and dynamic support such as STATCOMs. The benefits ofadvancing series compensation on the new transmission link between Whakamaruand Pakuranga will be evaluated also.The project cost falls within band E. This is a possible investment project to meet theGrid Reliability Standard and we anticipate seeking approval from the Commission inthe second half of 2012.6.4.2 Transmission capacity into Auckland and NorthlandOverviewPower transfer to the Upper North Island is dependent on:the generation from Huntly, and the transmission capacity between Huntly andOtahuhu, andgeneration from Whakamaru and south of Whakamaru, and the transmissioncapacity between Whakamaru and Otahuhu.For the existing system, issues that may arise during periods of high demand and lowgeneration in the Auckland area include:an outage of a Huntly–Otahuhu circuit may overload the other Huntly–Otahuhucircuit.an outage of a Huntly–Ohinewai circuit may overload the other Huntly–Ohinewaicircuit.the two 220 kV Otahuhu–Whakamaru circuits may overload during a contingency.an outage of the Hamilton–Whakamaru circuit may overload the two 110 kVArapuni–Hamilton regional circuits.an outage of the Hamilton–Ohinewai circuit may cause low voltage at theHamilton 220 kV bus.Approved projectsThe above issues will be addressed by the North Island Grid Upgrade (NIGU). NIGUincludes a number of projects which will:increase the power transfer capacity into Aucklandreduce the loading on the existing 220 kV Otahuhu–Whakamaru and Huntly–Otahuhu circuits, andreduce the reactive support needed in the Upper North Island (see Section 6.4.1).482012 Annual Planning Report © Transpower New Zealand Limited 2012. All rights reserved.