Analysis of Power Dissipation by Variation of Frequency on High Voltage Metal-Oxide Arrester Block
High voltage metal oxide surge arresters (MO-arresters) are requested to protect electrical power devices by limitation of internal or external transient overvoltages which occur in the high voltage power and distribution grid. The conduction of the surge arrester increases immediately after reaching a certain voltage level. Subsequently, it holds the voltage level, conducts the current, which is associated with the overvoltage, and ceases the high conduction period after reduction of the overvoltage. This significant effect of voltage limitation is accomplished through the highly nonlinear voltage-current curve of the metal-oxide ceramic material. Due to the height of high voltage MO-arrester and the resulting stray capacitances, it is obvious, that the voltage distribution along a MO-arrester is not uniform. This means, the upper MO-blocks are more stressed than the lower MO-blocks. Additionally, there are permanent superimposed alternating voltages which have a higher frequency than the grid frequency.
Both effects, higher voltages and higher frequencies, lead to superior stress for the MO-blocks because of the increased power dissipation. Experimental measurements are realised to verify the change of conductivity and permittivity at higher frequencies and temperatures. The voltage, current, frequency and temperature are measured at the same time. The voltage-current curve, the conductivity/temperature characteristic and the relative permittivity/temperature characteristic are used as an evaluation criterion. As a first result of these measurements it can be stated that a higher frequency causes an increasing power dissipation and results in an increasing temperature in the MO-block. This study presents and discusses the significance of the mentioned effects.