Capacitance measurements and tree length estimation during electrical treeing in sub-picofarad samples

A method for measuring capacitance below 1 pF is presented, which is used to measure dielectric properties during electrical treeing in XLPE samples. The measured capacitance is compared with finite element computations and from these simulations a simple relationship between the capacitance increase and the tree length can be established which corresponds well to the tree length observed by optical microscopy.