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National Environmental Standards for Electricity Transmission Activities: project examples of application (4 of 7)

Activities that may make up a transmission activities project:

  1. Relocation of poles to enable roading development
  2. Access track and mid span earthworks
  3. Work on towers involving rivers
  4. Undergrounding
  5. Adding a circuit
  6. Tower foundation cleaning and painting
  7. Thermal uprating on a 220kV double-circuit transmission line

Undergrounding

Project description: A developer has asked Transpower to take a 600-metres-long section of an existing 110kV line in a residential area underground, as part of a major subdivision project.

Activities required to complete project:

  1. A temporary line deviation on towers will be constructed while the new underground line is constructed.
  2. Erection of two new 25-metres-high termination towers to connect the underground cable into the existing overhead transmission line. The new termination towers will replace two existing towers and will be located 10 metres and 5 metres away, respectively, from the towers they will replace.
  3. The new underground cables will be buried 1000mm below ground and encased in a thermally stable backfill envelope of 500mm wide by 400mm high.
  4. A lightening rod will be placed on the top of both new termination towers and will be approximately 4m high.

The electric field associated with the new underground cables will be zero. The magnetic fields will be as follows:

Configuration Current rating (ampere) Magnetic field 1m above ground level (milligauss) Magnetic field at ground level (milligauss)
Trefoil 0.08m spacing 525 24.6 94.0
365 17.1 65.3
Main activities Status under NES
Undergrounding existing overhead line Controlled by regulation 12: the electric and magnetic field (EMF) has been modelled and complies with limits in regulation 10. 
Subsequent work on underground conductors will be permitted under regulation 11 if all applicable EMF conditions in regulation 10(2) to (8) are met.
Termination towers Termination towers are included in the definition of undergrounding, and covered in general terms by regulation 11.  The specific provision in regulation 15(3) clarifies that termination towers are controlled only if the provisions in regulation 14(3), (4) and (7) are complied with.  These conditions limit height increase, proximity to buildings, and replacing a pole with a tower. However, a termination tower does not have to be placed within the envelope for permitted activity of an existing tower and there is no limit on the increase in base footprint. Once in place, termination towers are treated as normal towers.
Lightning rods A  lightning rod is considered part of the tower, so  adding lightning rods is permitted by regulation 14.  The height limit is not relevant, because a lightning rod is not included in the measured tower height.
Temporary line deviation Permitted by regulation 17 (2), provided time limits on erection and removal are met – regulation 17(4).
Temporary structures Permitted by regulation 17, provided time limits on erection and removal are met – regulation 17(3).
Removal of overhead line Permitted by regulation 19 provided the site is restored – regulation 19(2) and (3).
Other potentially relevant activities Status under NES
Earthworks and vegetation clearance Earthworks and vegetation clearance are permitted, provided all of the relevant conditions in regulation 30 and regulation 33 are met.
Signs on support structures Signs are permitted by regulation 23, provided conditions under regulation 23(2) and (3) are met.
Noise from machinery and implosive jointing Noise from machinery and implosive jointing is permitted by regulation 37, provided it meets the limits in NZS6803:1999 Acoustics Construction Noise.

 

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Last updated: 18 January 2010