National Environmental Standards for Electricity Transmission Activities: project examples of application (7 of 7)
Activities that may make up a transmission activities project:
Thermal uprating on a 220kV double circuit transmission line
Project description: The existing maximum operating temperature of the double-circuit 220kV transmission line is 50°C. This allows current ratings for each circuit of about 206 MVA in summer and 251 MVA in winter.
The uprating project will increase the operating temperature of the line to 75°C. This will allow current ratings per circuit of about 299 MVA in summer and 329 MVA in winter. There will be no change to the voltage.
Increasing the operating temperature of the lines will cause additional conductor (wire) sag. This will reduce the distances between the conductors and the ground or structures underneath the line.
For some sections of the line, the reduced clearance distances could be less than those set out in the New Zealand Electrical Code of Practice 34:2001 (NZECP:34). For such line sections, additional work is needed to reduce conductor sag and maintain safe clearance distances.
In this example, all the work required will be carried out on existing structures and no new structures are proposed.
| Main activities | Status under NES |
|---|---|
| Increase the line's current rating | Permitted by regulation 10, provided that electric and magnetic fields are modelled and comply with limits (see section: Increasing voltage or current rating). |
| Minor tightening and/or retensioning of the conductors (nip & tuck) by cutting small lengths from the conductor, rejointing, and re-clipping the insulators – this is planned for eight spans on the 220kV transmission line | Permitted by regulation 6(3) without conditions. |
| Replacing vertical insulators with horizontal 'floating strain' (tension) insulators to raise the conductors by 1.5 to 2m (at the tower) – this is planned for eight towers Replacing hanger brackets (used to attach vertical insulators to the cross arms) with smaller fittings to raise the conductors a small amount – this is planned for 47 towers |
Permitted by condition 14 (1), as these components are by definition part of a tower. None of the conditions are relevant, as the structure is not being increased in height nor relocated. |
| Access to towers to re-clip insulators and replace insulators and hanger brackets | Use of access tracks to existing transmission lines is permitted – regulation 5(1). Maintenance, upgrading of tracks, or clearing new access tracks is covered by regulations for earthworks (section: Earthworks) and vegetation (section: Trimming, felling, and removing trees and vegetation). |
| Strengthening towers may be required if the structural load on the towers increases (eg, replacement of vertical insulators with floating-strain insulators). This involves replacing steel angle members of the tower with stronger sections, or installing additional members | Tower strengthening would be permitted by regulation 14 (1). There are no applicable conditions: the tower height and base footprint will remain the same and the tower will not be moved. |
| Changes in loading of a structure may require foundation strengthening. This would mean excavation of the foundation backfill, replacement with concrete, and reinstatement of the surface | This would be permitted by regulation 31, provided vegetation clearance conditions are complied with. The earthworks would be permitted by regulation 33, provided the earthworks conditions are complied with. |
| Noise from machinery and implosive jointing of conductors | Noise from machinery and implosive jointing is permitted by regulation 37 provided it meets the limits in NZS6803:1999 Acoustics Construction Noise. |
Last updated: 18 January 2010
