Characterizing of corona rings applied to composite insulators

In this paper, the electric field stress is investigated for a set of composite insulators. Three designs of such insulators, with different dimensions and shapes, are used to build a model of a composite system. The critical values of electric field are determined for 230 kV and 400 kV voltage classes. The field is calculated via a set of basic equations, reflecting the influence of several factors such as voltage, material and corona ring parameters on the insulator aging. The impact of corona rings on reducing electric field stress is determined for different voltages and insulator designs using the concept of efficiency. The ring parameters are optimized to determine their impact on reducing the field stress on the insulator. Therefore, a MATLAB-based code is set to cater for a wide range of parameters and to determine the optimal dimensions and locations of such rings. In all studied cases, the Finite Element techniques are used as a simulation tool for analysis, field contour plotting and stress monitoring.

► The role of corona rings in reducing electric field stress was discussed for three types of composite insulators.
► An efficiency factor was introduced to quantify the impact of corona ring on reducing the field stress.
► The grading efficiency was computed as a function of voltage applied, insulator design and corona ring parameters.
► The variation of corona ring frame diameter has the highest impact on field reduction, whereas, the ring location has shown the lowest influence.
► Insulators for voltages above 132 kV should be equipped with corona rings as part of insulation system.