The cause of the August 3rd outage was related to a failed speed signal to the Whitehorse Hydro Unit #4 governor. The governor controls the electrical output from a hydro unit. The failure of this speed signal causes the hydro unit to shut down as a safeguard to prevent the unit from becoming uncontrollable. The loss of the speed signal was caused by a control board failure. The equipment was repaired, tested and the unit was placed back on line. Whitehorse Hydro Unit #4 is the largest hydro unit on the grid. When the generation was lost, the feeders tripped off in an attempt to balance the customer load to remaining generation.
We have had a few calls from residents of the Marsh Lake area, wondering what lake levels are expected to be over the next month or two. Below is a chart that offers some information. The solid green line shows the water levels to date. The dotted green line shows expected levels for the rest of the summer and fall, with the greyed out area indicating variations depending on how much rainfall the area receives, and the local temperatures. The blue and purple lines show the lake levels for the previous two years.