Power distribution is a complex network of generators, high voltage cables and transformer sub stations. To optimise the network, monitoring has to be performed at strategic points. Measurements of under voltage and over currents are made by devices called protection relays. The information is communicated to a central control office from where changes can be implemented to ensure efficient and reliable operation of the power grid. Because of their proximity to power switching devices, protection relays are tested with high voltage insulation and damped oscillatory wave impulses.