N.L. Hydro scrambling for answers after high-power Muskrat transmission test fails

Utility experts in Newfoundland and Labrador are scrambling for answers after a high-power test of the Muskrat Falls transmission line ended in failure, with future tests on hold.

Some 58,000 customers lost power for up to 25 minutes Thursday morning after Newfoundland and Labrador Hydro energized the troubled Labrador-Island Link known as the LIL to 700 megawatts.

It was the biggest test yet for the 1,100-kilometre high-voltage line from Muskrat Falls to Newfoundland's Avalon Peninsula, with previous tests at about 500 megawatts.

The high-power test began at 10 a.m., and initially went well, with energy flowing over the two lines to Soldiers Pond on the Avalon Peninsula, and over the Maritime Link to Nova Scotia.

The LIL is designed so that if one of the two lines stops transmitting power, the other linecan carry the entire load, up to 900 megawatts.

But after one of the lines was intentionally tripped in order to test the system's overload feature, something went wrong and the link lost power.

The sudden loss of 700 megawatts meant large blocks of customers lost power temporarily while backup systems powered up and stabilized the grid.

In a call Thursday afternoon with reporters, Hydro vice-presidentRob Collettsaid the incident is being investigated.

"This could have been a sensor, equipmentor software issue. Our experts are going through the sequence of events," said Collett.

Future testing on hold

The testing is one of the final steps in the commissioning process for the link, which has been plagued by computer software glitches and synchronous condenser vibration problems at Soldiers Pond.

The plan was to test the overload capacity of one line this week, and the second line next week. But Collett said those plans are now on hold and future testing will depend on the outcome of the investigation.

"It might be simple and testing can resume in the next couple of weeks.If this is found to be more substantial issue this could be take some time to resolve.It could go either way," he said.

The Muskrat Falls hydroelectric generating station, with a capacity of 824 megawatts,was commissioned a year ago. But GE has struggled to complete the power line that brings Muskrat's zero-emitting electricity to Newfoundland and Nova Scotia.

The link has been operating at around 300 megawatts, helping displace costly and polluting oil-fired electricity at the Holyrood generating station.

Collettdescribed Thursday's setback as "significant" and that the interruption of power was regrettable. But he said the testing is necessary in order to ensure the link's future reliability.

"We are crawling our way out of the trench," he said. "We are closer to the finish line than we've even been."

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