City: back-to-back transmission circuit outages caused power failure in Lethbridge
LETHBRIDGE, AB – Wednesday’s powerful wind gusts causing rare back-to-back transmission circuit outages here in Lethbridge.
Both provincial grid connections at one of six supply substations caused power outages for about 25-percent of the city just after 9am.
The follow up investigation has verified that equipment operated correctly but the extreme wind gusts of up to 125 km/hr likely forced the power lines to slap together causing power flow swings.
Compliance and Controls Manager Tracy Brason says the grid is designed to be able to survive the loss of a single circuit but this was an extremely rare event that impacted two independent key assets almost simultaneously.
On top of that, crews had to deal with several outages and downed wires caused by fallen trees.
On the plus side, Brason says while neighbouring communities are dealing with dozens of downed wooden power poles, none here in the city sustained damage.