An Automatic Device for the Measurement of the Growth of Water Trees

An automatic device for the measurement of the growth of water trees as a function of time is described. The system is based on video camera signal processing of the images of water trees through a microscope. Water trees are grown in laboratory specimens using the water needle method. At regular intervals, specimens under test are successively placed under the microscope and any change in light transmission along the axis of the water tree is detected and stored in a memory device. Several examples of results obtained with the device are presented. Due to its high sensitivity it allows new observations such as, for example, residual growth of water trees after the voltage switched off. The device allows study of the growth mechanisms of water trees as well as comparisons of the resistance of translucent materials to water treeing.