Most of Central Otago and a large tract of the Queenstown Lakes District have no security of energy supply, a former Delta engineer says.
Clyde man Steve Tilleyshort, who worked for Delta under contract to Aurora Energy, said a widespread power outage like that experienced in Clyde on June 14 could hit any one of 10 sites throughout the region all running on one transformer instead of the standard two.
The outage was due to the single transformer at the Clyde-Earnscleugh substation failing, cutting power to 1200 homes and businesses for about nine hours.
The second, backup generator, at the zone substation failed in 2017 and had not been replaced.
This was the problem, Mr Tilleyshort said.
‘‘A good network should have multiple options to consumers.
‘‘Multiple supply options to zone subs should exist everywhere and all zone subs should have two transformers.’’ That was a minimum standard, he said.
The network in Central Otago and into the Queenstown Lakes District fell well below that. Mr Tilleyshort said only three of 13 zone substations throughout the region had two transformers.
That left 10 vulnerable to outages similar to that experienced in Clyde.
They are Roxburgh, Queensberry, Lauder, Omakau, Camphill Rd (servicing Hawea Flat and Makarora), Lindis Crossing (Tarras), Ettrick, Earnscleugh, Earnscleugh-Clyde, and Cardrona.
Camphill Rd, Omakau, and Lauder were particularly vulnerable because they all ran off a single transmission line.
‘‘Basically, any incident that takes down the line from Alexandra to Omakau snowballs on to Lauder and into the Ida Valley — power is cut to that whole area.
‘‘The same applies from Wanaka to Hawea Flat and Makarora.’’
Hawea Flat included a massive dairy farm operation that ran five dairy sheds and more that 21 centre pivot irrigators.
That operation alone drew more electricity than all of Clyde but the supply to keep it running was far from secure, Mr Tilleyshort said.
There were also ramifications for orchards and vineyards, should frost-fighting equipment fail at a critical time.
He acknowledged he could only work within the scope of his job in his 17 years contracted to Aurora but the state of the network was an embarrassment to him.