Using data to find faults faster

Much of the Coromandel Peninsula is powered by a 66kV electricity ring circuit which goes between Kopu and Tairua, up to Whitianga and back down to Kopu. Cyclone Gabrielle’s force in February 2023 saw that ring circuit hit with multiple faults, cutting power to thousands of customers.

Tairua, Pauanui and surrounding areas, from Hot Water Beach in the north to Hikuai in the south, were particularly badly hit, with about 4,800 customers losing power because of faults on both sides of the ring circuit, meaning we couldn’t re-route electricity to them another way.

Finding where faults are and getting crews into the correct locations, in often very remote areas, is a challenge on the peninsula, particularly following the cyclone, which led to numerous landslips and road closures.

That’s where distance-to-fault data from protection relays played a pivotal role in the power restoration effort during Cyclone Gabrielle.

How it worked

Network Performance Engineer East Peter Manning explains:

“The protection relays give distance-to-fault information, which can be in two ways. They can give a fault current level that we can put into our modelling software, and we can then work out from the fault current that flowed through the circuit, how far down the circuit the fault is.

“They can also give the information themselves and record, for example, the fault is 28% down the total line length.

“The power is fed from Transpower at their Kopu GXP (grid exit point) and their circuit breakers record the information and provide the protection for those circuits. Their circuit breakers open when there’s a fault.”

That’s where Senior Protection Engineer Michael Allpress and his contacts at Transpower came in. After the team realised early on 13 February that they couldn’t restore supply to Tairua and surrounding areas, he contacted Transpower, who remotely downloaded their protection relay information.

Says Peter: “Michael told me the percentage of distance on the line that the fault was, I opened up the GIS package and measured along the line until I got to that distance along the line, recorded the closest pole number and that got reported out to the guys in the field.”

The data indicated a phase-to-ground fault at 28.25% of the line length – approximately 9.11km along the line.

Access issues

Unfortunately, roading access issues (only emergency vehicles were permitted on the road) meant our fault crews were unable to get to the fault location straight away.

“The conditions were challenging as the cyclone was still in progress. Fault crews tried using motorbikes to access the rugged cross-country terrain, but they had to withdraw as trees were falling around them and it was too unsafe to continue.”

A helicopter patrol was carried out the following day once conditions had eased.

“The calculated fault position gave the helicopter patrol a good indication of the possible fault location. The actual fault location was found within two spans of the calculated position.

“With an event like this, to get within two poles of the actual fault location gives you a better confidence in using the technology.

“The following morning, the Downer line crew rode motorbikes in as far as they could go. They then walked the rest of the way to the pole site. A helicopter flew in materials, tools and ladders to the crew to carry out the repairs.”

The fault was caused by a string of glass insulators failing in the high winds, causing the line to fall to the ground.

Without the data, the crews would have needed to patrol the entire line, from the very start at Kopu GXP, all the way over the hill to Tairua, looking for information to suggest where the damaged equipment could be.

“It was a great team effort across both Powerco and Downer to find and repair the fault and restore power in this timeframe (two days). I know there was lots of positive feedback from the community about this fault response via social media and in person.”

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