Transpower optimises upper North Island power delivery

Article – BusinessDesk

By Gavin Evans

Oct. 8 (BusinessDesk) – Transpower is changing the way it manages some of its most important lines in order to defer upgrades and deliver more electricity over the course of a day.

The national grid operator last week moved to two-hourly ratings on five circuits in the Bay of Plenty, the central North Island and south Auckland. This week a further three circuits in the upper North Island will move to 12 daily ratings from six previously.

The variable line ratings adjust the amount of power the lines can carry based on the expected temperature. In the middle of the night they can deliver more electricity before starting to sag; in the middle of the day they can carry less.

Transpower says the greater granularity offered by the 12 daily time periods should let it more effectively manage the critical morning and evening peak times in areas of fast-growing demand, such as South Auckland.

“VLR also helps more generation to be exported at times when it might otherwise be constrained, and avoid water being spilled at the hydro lakes.”

State-owned Transpower operates more than 12,000 kilometres of lines linking the country’s largest power stations with major consumers and local network companies. It is making more use of new technology to defer line upgrades where possible and make its processes more responsive to more variable generation from wind and solar.

Transpower started trialling VLR in 2010 on lines that are nearing maximum loads. The rest of its lines have set day-night and summer-winter ratings.

Studies done at the time indicated the change could provide about 10 percent more capacity and defer costly upgrades. The savings for South Auckland taxpayers were estimated at about $15 million. The benefit from greater access to lower-cost generation was estimated at $5 million annually.

Two of the eight circuits using VLR deliver electricity to Otahuhu. Others link Kinleith, Lichfield and Tarukenga, and Wairakei, Ohakuri and Atiamuri. The two lines between Kawerau and Trustpower’s Matahina hydro dam were added to the VLR programme last week.

Transpower says VLR is likely to become more critical as the grid becomes more dependent on wind and solar generation.

“We expect suppliers of our operating network systems will add VLR as a standard feature making its wider use more feasible.”



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