HVDC and impulse tests for hotline insulator washing and change-out on BPA´s HVDC Intertie

HVDC tests were performed to establish parameters and techniques to safely hotline high pressure wash insulator strings on BPA´s section of the DC Intertie, energized at ±500 kV. Parameters investigated included nozzle distance from the conductor, water pressure, nozzle orifice, water resistivity, and washing technique. Switching impulse tests were performed on nonceramic suspension insulators for the DC Intertie Line. These tests were performed in response to change-out of glass strings to nonceramic while the line is energized. The purpose of the tests was to ensure that the change-out could be performed safely. In particular, the tests were to determine if the withstand voltage of the tower air gaps would be high enough during all parts of the change-out. The withstand voltage should not be lower than an assumed maximum switching surge of 900 kV. The tests were performed on a simulation of the DC Intertie tower, using the setup of hotline tools used by the line crew during the change-out. Tests were then performed on tower conditions in the same steps that would occur in the change-out