Extreme and fluctuating weather conditions, including high humidity, below-freezing temperatures, and ice storms can cause ice to form on power lines. We remove ice from power lines as quickly as possible to prevent equipment breakage and loss of power. Ice weight can put a lot of stress on power lines and damage equipment. In windy conditions, icy lines can whip violently and gallop, causing tie wires to break, wood poles to snap, and even steel towers to crumple.
A roller, attached to the end of a long pole or rope, is hung onto a conductor. In windy or wet weather, the power is turned off; in some weather conditions, it can be left on. The roller is pulled along the power line, cracking the ice off as it goes. This is a manual procedure often done in freezing rain and storm conditions. Rolling is done when melting is not an option. A 10-person crew can de-ice roughly 1.6 kilometres of line per hour.
Ice melting may require us to shut off the power to certain customers, but it's a short-term outage that can help prevent significant equipment damage resulting in longer outages. Power is cut to a certain section of lines, and the customers serviced by those lines, for 1–3 hours. A controlled short-circuit is placed at one end of a sub-transmission line. The current flow creates a gradual temperature increase that heats up the line and melts the ice. Melting can only be done when the outside temperature is –7 C or higher. Using 2 crews of 3–4 people each (one crew working outside on the equipment and the other crew working in a control room), we can melt the ice off 30–50 kilometres of line in about 3 hours. We developed the ice melting process more than 30 years ago and we're recognized as leaders in the field.
Ice-covered power lines and high winds pulled and twisted this tower in 2012.
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High winds and freezing rain can cause transmission lines to gallop.