This paper presents a method for, and the results of, condition assessment of toughened glass insulators removed from service on HVDC transmission lines.
Manitoba Hydro’s HVDC lines Bipole 1 and 2 are energized at 450 kV and 500kV and have been in service since 1972. During the 40 years following installation, no condition assessment of the insulators has been made beyond visual examination.
In 2014, it was decided that tests would be carried out in order to determine the remaining life of the insulators. Tests were conducted at the Sediver research and testing facility in St. Yorre, France, and were witnessed by a member of the transmission line design group from Manitoba Hydro.
The insulators to be tested have experienced various levels of stress dependant on placement on the lines.
- In the southern portion near Winnipeg, Manitoba, Canada, the terrain is open and flat with cultivated fields and little protection from wind.
- Near the center of the line and to its northern end the terrain transitions to boreal forest.
- Over 40 plus years in service the Bipole insulators have faced high levels of vibration, icing and ambient temperatures of -45 to 40 °C.
- Contamination levels range over the course of the line from very light to light.
Because of the diversity of conditions existing over the 895 km length of the bipoles, the insulators to be tested needed to be selected to provide a representative sample. Insulators were removed from both bipoles and both polarities. Sites for removal of insulators were chosen near both ends of the bipoles near Winnipeg and Gillam, Manitoba, and the approximate center of the lines at Grand Rapids, Manitoba.
For each of the three locations, two strings were removed from the energized lines, one deadend string of 29, 220 kN standard profile insulators and one suspension string of 21, 180 kN fog type insulators.
At the time of removal, samples of surface contamination were taken and later tested for Equivalent Salt Deposit Density (ESDD) and Non Soluble Deposit Density (NSDD). In total, 150 insulators were removed and shipped to St. Yorre for testing.
Tests conducted at the Sediver research and testing facility were conducted in accordance with the latest CSA standard C411.1-10 . Several tests were performed including galvanizing tests, electromechanical failing load tests, residual strength tests and thermal-mechanical performance tests.
The results are included in this paper and indicate that the samples show little to no sign of aging or degradation with all insulators performing at levels expected from their rating. The investigation into the remaining life of the insulators provided clear evidence and information which has proved useful to the Manitoba Hydro asset management group.
The results show that the insulators will almost certainly perform for another 40 years or more. Further, in the current context where utilities and designers consider life cycle costs in selecting suitable components for new transmission line development, these tests also confirm the expected long-term durability and reliability of toughened glass insulator technology.