Development of a computer model to predict risks from an electrical bushing failure

摘要

Failures have led to the destruction of in-service, porcelain-clad, high voltage electrical bushings. These failures can result in porcelain fragments flying significant distances, 50 m or more, with a mass and velocity high enough to cause serious injury and damage to structures and equipment in and around a substation. In order to predict the risks to people and equipment from a failed bushing it is necessary to know the velocity, mass and distance travelled by the resulting fragments. Boiling Liquid Expansion Explosions (BLEVEs) generally result in five or fewer fragments. Failed porcelain bushings can produce hundreds of fragments, hence data from BLEVEs cannot be used to predict the risks from bushing failures. To obtain data, bushings were deliberately made to fail under controlled conditions with varying internal pressures from 13 to 75 bar (1.3 to 7.5 MPa). The position, weight and distance travelled by each fragment were measured, with the largest fragments, over 1 kg, travelling in excess of 100 m. The data was used to calibrate and validate a computer model that uses Monte Carlo techniques to determine the initial properties of fragments and a trajectory model to predict the flight of the fragments, including multiple impacts with the ground, lift due to the fragments spinning after the first impact and drag. The computer model predicted the distance travelled by the fragments to within 10 m (10%).