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Commissioning approaches in Northpower Ground Fault Neutraliser trial

Published on December 4^th 2009, 10:24am

It is hoped the system will reduce the number of outages caused by earth faults, where tree branches or possums contact high voltage lines for example, by up to a third.

The GFN is manufactured by a European firm, Swedish Neutral, and the units are distributed in New Zealand by Christchurch lines company Orion.

GFNs employ resonant earthing with an additional ‘residual current compensation feature’ which involves injecting current into an arc suppression coil at 180° out of phase with the residual fault
current.

Sales and technical support manager at Orion Steve MacDonald reports that several networks have ordered GFNs, and the company is also serving a customer in Australia.

Outside of units operational on Orion’s network, there is currently one GFN commissioned in New Zealand and one in Australia.

Northpower’s unit has been installed at the Poroti substation, and is currently in the process of commissioning. Network planning manager Russell Watson says operating the unit has required some adjustments to network operation, though it is hoped the GFN will be fully operational by year’s end.

“We are working on some technical issues, not related to the equipment itself, but to some aspects of our network and the way we tune it. We’ve had to do some analysis, and we’re in the process of making some little changes in our network that will hopefully balance it out,” he says.

One expected benefit of the system is easier identification and elimination of small, hard to identify disturbances. The system can tune out a fault, rather than trip out the whole line.

“Where you’ve got a cracked insulator or a fault in a surge arrester, it may look OK, but every time it rains the crack in the insulator conducts and trips out but it doesn’t have enough energy to blow the thing apart, so you’re looking up and down over many kilometres of line and you can’t find anything.

“Those sorts of faults don’t happen that often but when they do they’re very hard to track down, and they create a real nuisance for the farming community,” says Watson.

The total project cost is around $250,000 to $300,000, though should the company elect to carry out a commercial rollout it is expected costs would be reduced through the benefit of greater scale and experience.

Before making a decision on whether to push ahead with further GFN installs Northpower plans to run the equipment for an extended period of time, logging and evaluating the results.

“Even once we install it, it will take some time to get a history of how it performs and what it’s really saved, because faults don’t happen every day. We’ll keep a note of how many faults it tunes out and how many it doesn’t, and over a year or so we’ll get a good feel for how much of an improvement it’s made,” says Watson.

Read the article at energynews.co.nz

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