110 kV Line Commissioning EMF Investigation

Waipa Networks is in the final stages of stringing a new 110 kV transmission line between Transpowers Te Awamutu and Hangatiki Substations.  The line has been installed in close proximity to the KiwiRail owned main trunk line along this 30 km section of the Waikato region.  Mitton ElectroNet has been liaising with Waipa Networks, KiwiRail and other interested businesses in the vicinity, to carry out a number of investigations ensuring influences by the new line are acceptable.

Mitton ElectroNet has completed testing and reports are being prepared for issue to the relevant parties. Electric and Magnetic Field (EMF) testing was been carried out to benchmark the levels in the vicinity of the new line. Pre-commissioning testing has been completed whilst the line is de-energised to obtain  bench mark  values.  Once commissioning is complete and the line is energised, the EMF test will be repeated so that the impacts of the new line can be identified and referenced against prescribed limits.

A simulated fault was set up on the line to measure a number of different scenarios.  One of these, is to measure touch and step voltage safety at various poles along the length of the line in the event of an earth fault occurring. By performing current split measurements at the pole foundations the influence of the OHEW can be assessed. Isolating the earth return current through the pole foundations enables the pole footer impedance and EPR contours. The measured values can be scaled against the actual fault current to simulate results if an actual fault was to occur at the pole.   

We are also working closely with KiwiRail to ensure that there are no undesirable voltages induced onto their signalling circuits. Injecting a 58 Hz current in the overhead line allowed induced voltages in the KiwiRail circuits to be measured. Injecting at 58 Hz enables the test signals to be isolated from any other noise or interference on the earthing system (such as 50 Hz and harmonics). The measured values can be scaled against the actual fault current to simulate the induced voltages that would appear on the Kiwirail circuits under fault conditions on the 110 kV line.