Classification of Over voltage (Insulation Coordination Study)

This post describes the need for an Insulation Co-ordination study and the causes and types of over-voltages in the Power system.

Insulation Coordination:

Voltage stresses in power systems can have internal or external origins. Overvoltages can be caused by faults, switching operations, or lightning strokes. In addition, they can occur with a very wide range of waveshapes and durations. Dielectric failures in power systems can cause tripping of the protective devices, destruction of equipment, or interruption of operation. The breakdown characteristics of the different types of insulation depending on the configuration and environment of the insulation, as well as on the waveshape and duration of the applied voltage. On the other hand, both stresses and withstand insulation voltages may exhibit random behavior. Therefore, it is important not only to assess the overvoltages that can appear on a given component but the behavior of its insulation taking into account that stress and withstand characteristics may be random.

Insulation coordination is defined as the selection of the dielectric strength of equipment in relation to the voltages which can appear on the system for which the equipment is intended and taking into account the service environment and the characteristics of the available protective devices. In an insulation coordination study, the voltage levels of power system equipment are determined in order to ensure the protection of equipment against overvoltages. This proper design in terms of the insulation coordination provides the reliability of the system by decreasing insulation failures and reduces the cost of the system by preventing oversizing of the equipment. Hence, insulation coordination is an important study for power systems in order to prevent failures and overinvestment.

Power systems are always subjected to overvoltages, which are usually the result of faults, sudden changes in operating conditions caused by switching operations, or the impact of lightning strikes. Therefore, the over voltages can occur due to external agents such as lightning or due to internal agents such as switching operations, load rejection, and internal faults. Etc.,

Purpose of Insulation Coordination:
To ensure that the probability of insulation breakdown is limited to an acceptable value and that any breakdown is restricted to self-restoring insulation.

System Transients in Power Systems:

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