For 30 years, Hydro One’s line technicians have washed insulators on live low-voltage and high-voltage lines. Two years ago, however, the utility developed a method to wash the insulators on live 500-kV transmission lines from an aerial lift. This method more than doubled the utility’s productivity, increased worker safety and eliminated most planned circuit outages.
Up until two years ago, Hydro One had to take its 500-kV circuits out of service for insulator washing. The circuit outages were getting tougher to get and hold onto because of system problems or other issues that came from the regulator. Also, the company wanted to get all of its insulators washed before the winter set in.
Investing in Aerial Equipment
As the largest electricity transmission and distribution company in Ontario, Canada, Hydro One operates a 29,000-km (18,020-mile) high-voltage transmission network and a 123,000-km (76,429-mile) low-voltage distribution system. The utility operates 97% of the high-voltage transmission grid throughout Ontario and serves 1.3 million customers in rural areas across the province. Owned by the province of Ontario, the company operates 287 transmission stations, 1,007 distribution and regulating stations, and employs more than 5,000 full-time and almost 2,000 part-time workers.
The utility also owns close to 7,000 vehicles and other pieces of equipment in its fleet, including several unique aerial devices such as machines equipped with insulated truck-mounted aerial work platforms. The technicians use these machines for live-line work on transmission lines, tower maintenance and any other work requiring overhead access. Hydro One currently owns two Bronto Skylift aerials: a 197-ft platform height Bronto SI-197 HDT and a 156-ft Bronto SI-156 HDTC, which is mounted on a Track Industries HT 500XL all-terrain carrier.
The Hydro One field workforce can use the SI-197 to reach towers near access roads and use the SI-156 to reach most remote towers with no access roads because of the lower ground-bearing pressure of the track-mounted carrier. The utility also owns a road-going Bronto SI-155 insulated aerial, which incorporates a water line running through the inside of the boom, alongside the standard hydraulic and electric lines from the base of the machine to the platform area. This machine is suitable for a wide variety of jobs including washing insulator skirts.
Hydro One washes the insulator skirts on most towers at least once a year. Through the washing process, the technicians strive to remove the airborne particulates including dust, industrial contaminates, insect and bird debris, and salt residue. Cleaning enhances the life of insulators, improves their performance and reduces the potential for conductivity. If not routinely cleaned, electricity can jump across the insulator from the hot side to the cold side, causing a flashover; this can cause power outages and damage equipment, resulting in costly repairs. Most flashover outages are also unpredictable and take several hours to remediate.
Washing the insulator skirts on the towers used to be a time-consuming project before Hydro One started using the aerial device on live-line towers. Previously, the utility had to shut down the circuit to allow its technicians to clean the skirts.
Jeremy Meiers, transmission technician for Hydro One, says that because of the location of the towers and the provincial outage restrictions, his crew would be lucky to get three or more towers done in one day. Now that they can wash a 500-kV live line, they only need to enter the right-of-way at each location annually and can get to multiple towers on multiple circuits. As a result, he says it has been a big time saver for Hydro One. The technicians can now wash as many as 10 to 12 towers in a single day, and they can do it without shutting down the lines.
Also, they’re able to do the job much more safely than in the past. Before the technicians started washing insulators from the Bronto, they had to climb up the side of the tower carrying the water hose and washing gun. Then, they had to get into position to wash an insulator string. Just climbing the 180-ft tower wore out some of the technicians, and once they were in position to reach the insulators with the water stream, it took time to properly clean the string.
Insulator strings on Hydro One’s 500-kV lines normally consist of 23 hardened glass skirts of varying sizes and shapes to help prevent ice build-up. Technicians thoroughly wash each skirt; they know the skirts are properly cleaned when they can “hear the bells ring.” Once the string is clean, the technicians climb down to the ground level and climb up the tower to the next washing position. This work can be time-consuming, hard on the technicians and potentially dangerous. Now, washing insulator strings from the aerial platform eliminates this danger and much of the time spent on each tower.
Designing a System to Work Live
Hydro One started live-line washing 500-kV lines a few years ago after working with Jeff Harris of Hycotec Inc., a Bronto Skylift dealer in Caistor Centre, Ontario, to modify its Bronto SI-155. The utility wanted to run a high-pressure water line through the inside of the telescoping boom on its machine from a quick-connect fitting on the base to one at the top of the telescoping boom section. A flexible line mounted on the outside of the fiberglass-insulated boom section connected this fitting to one just below the floor of the platform. With this arrangement, Hydro One could easily connect a hose from a mobile water truck to the fitting at the base and a hose from the upper connection to a water gun.
Harris helped us design and install the system, and worked with the utility to develop proper procedures for safe operation. For washing applications, the technicians only use de-ionized water with a water temperature of less than 80°F in the water truck. This lowers conductivity and helps reduce the chance of flashovers. Most of Hydro One’s water trucks hold 1,000 gal or more, and an on-board pump pressurizes the water line to between 750 lb to 1,000 lb at the gun nozzle. When exiting the washing gun, the pump produces a pulsing action where the water stream is not continuous; it is constantly interrupted with minute gaps of air, which helps eliminate arcing.
Keeping the insulators clean is particularly important in the Greater Toronto Area (GTA) corridor. The corridor is parallel to the highly salted 407 Highway on the north end of Toronto and contains four double-circuit 500-kV lines on 180-ft towers along with other 230-kV and 115-kV lines.
As with all jobs, when the Hydro One crew arrives at the GTA right-of-way site each morning, they hold a mandatory tailgate meeting to review safety procedures, job-site specifics and project objectives. Following the meeting, it takes the crew less than 20 minutes to position the Bronto aerial and water truck, raise and level the aerial’s chassis, and ground the machine and the entire washing system from the ground up to the wash gun’s nozzle. Then the crew must elevate the washing technicians to the overhead area. Since they are working around live-line towers, they use a hand-held range finder on the platform to help the operator maintain a safe distance from the live lines and avoid flashover.
Every Hydro One crew member has been cross-trained to operate the Bronto aerial, and each takes turns performing the washing function and other tasks on the site. In addition, one crew member on each job site where a Bronto is being operated has completed an advanced training and certification from Bronto in all aspects of the machine’s operation. This crew member remains near the ground controls of the machine at all times when someone is elevated. This provides an extra level of safety in the event of an unforeseen occurrence.
Today, when Hydro One needs to perform insulator washing on any of the towers in its high-voltage transmission network or its low-voltage distribution system, the utility is doing it faster, safer and more efficiently than ever before using the Bronto SI-155 aerial work platform. And, since the utility doesn’t need to de-energize the lines to perform routine maintenance and the technicians do not need to climb the towers, using an aerial to do insulator washing has helped to save time and improve productivity in the field.
Hugh Crockett (hugh.crockett@HydroOne.com) is the superintendent of transmission lines for Hydro One in Mississauga, Ontario, Canada.
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