Insulation coordination of ehv systems – an overview

The reliability of power supply provided by an electric power systemis judged by the frequency and duration ofsupply interruptions to its customers. Althoughthere are many causes of interruptions, breakdown of insulation is one of the most frequent.The insulation provided to the equipment has to withstand a variety of stresses(overvoltages) with varying shapes, magnitudes and duration during its service period.We cannot prevent these overvoltages in an electric network,so we need to protect against them. The main objective of Insulation coordination is to ‘Design the system insulation of all power system components to minimize power interruptions and damage resulting from steady-state, dynamic and transient overvoltages in an economic fashion’.To keep interruptions to a minimum, the insulation of various equipments of the system must be so graded that flashovers occur only at intended points.

The magnitudes of over-voltages are usually limited to a desiredprotective level by protective devices. Thus the insulation level of the equipment has to be above the protective level by a safe margin. This paper attempts to give an overview of concepts of insulation coordination and the different methodologies of insulation co-ordination studies.