Planning inputs

National Grid

North Island

The main transmission grid in the North Island comprises of 220 kV and 110 kV lines connecting major demand centres with generating stations. North Island generation is spread throughout the island and is based on a number of generation technologies: hydro, conventional thermal, combined cycle gas, co-generation and geothermal.

Most of the generation plants are located some distance from the major demand centre in the Auckland region. The North Island is also supplied by the high-voltage direct current (HVDC) line that runs from Benmore substation in the South Island to Haywards substation near Wellington.

South Island

The transmission grid in the South Island consists of 220 kV, 110 kV and 66 kV lines. All major generation in the South Island is from hydro stations, with most generation sources in the Waitaki and Clutha Valleys.

The National Grid is made up of the following assets:

Asset Description Detail
Length of HVAC and HVDC Transmission Line 11730 km
HVAC Transmission Line Voltages 220, 110, 66, 50 kV
HVDC Transmission Line Voltages 350 kV
HVDC Link Capacity 1200 MW
Substations 178
Capacitor Banks 86
Transformers (Banks – excluding HVDC) 350
Synchronous Condensers 9
Static Var Compensators (SVC)/STATCOMS 8


Demand assumptions are a key input into our future planning.  Our forecasts, and documentation outlining our forecasting approach, can be accessed at the links below.

Each year, we consult with industry on our demand forecasting approach, assumptions and results.  For the 2016 year we received feedback from the Ministry of Business Innovation and Employment (MBIE) and the New Zealand Institute of Economic Research (NZIER). This feedback was sought after public consultation on the draft Electricity Demand and Generation Scenarios (EDGS) suggested that MBIE should take a role in validating Transpower’s peak demand forecast.

MBIE asked NZIER to undertake a high-level review of Transpower’s forecasts and methodology.  NZIER’s memo stressed the value of simplicity and transparency in our forecast methodology and suggested some changes to our approach. We have considered their recommendations and have, in consultation with MBIE and NZIER, implemented a number of changes aimed at increasing confidence in our forecasts.  These changes have not required fundamental changes in the model specifications and data requirements.  More detail on this can be found in the Information document below.

Comments on the approach, input assumptions or results are always welcome.


Email us if you have feedback or queries


Like demand, the make-up of generation both now and in the future is also a key input into our planning. Future generation will comprise a mix of existing generation (adjusted for decommissioning), new committed generation, and other potential generation developments like distributed generation (including solar PV). The uncertainty surrounding future generation requires the consideration of a number of possible generation scenarios.

In 2015 the Ministry of Business, Innovation and Employment published a draft Electricity Demand and Generation Scenarios (EDGS).  Independent generation scenarios are a key reference point for preparing and assessing Transpower's major grid investment proposals, and we will be required to use the EDGS when developing major capital expenditure proposals.

Read about generation assumptions in the Transmission Planning Report.

Grid Support Contracts

Transpower has developed a Grid Support Contract (GSC) Product. GSCs assist Transpower to manage risks resulting from any construction delays, higher than forecast demand growth or major asset failure, and to defer some transmission investment under certain conditions. The scope of the standard contract includes consideration of all forms of non-transmission options including large and small generation and both aggregated and distributed demand side participation (DSP).