Informatics Publishing Limited

K. S. Meera ¹, M. Kanyakumari ²

Affiliations
1 Additional Director, Power System, Division, Central Power Research Systems, Banglore, IN
2 Additional Director, High Voltage Division, Central Power Research Systems, Banglore, IN

Abstract

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.

Keywords

Insulation coordination, overvoltages, transients, Basic Impulse Insulation Level

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M. Kanyakumari ¹, R. S. Shivakumara Aradhya ²

Affiliations
1 CPRI, Bangalore, IN
2 Lamco Industries Pvt. Ltd., Hyderabad, IN

Abstract

Zinc oxide (ZnO) surge arresters are being used extensively in high voltage power systems for providing protection to the transmission lines and the associated substation equipment from over voltages caused due to lightning and switching surges. It has been observed in practice that the voltage distribution in a tall multi-section arrester under normal operating conditions is quite non-uniform. As a result, the ZnO blocks at the top section share higher voltage and hence higher thermal stresses than the ZnO blocks at the bottom section. This leads to accelerated thermal aging of the blocks at the top if proper measures are not taken to make the voltage distribution uniform along the entire length of the arrester. Generally, provision of grading rings is a common method for achieving uniform voltage distribution through out the length of arrester. In this paper, the results of the optimization of the grading ring dimensions for a 765 kV system arrester with a rated voltage of 624 kV using Finite Element based 2D Elecnet software are presented.

Keywords

Grading ring, Zinc oxide surge arresters, Voltage distribution of arrester, Electric fi eld distribution.

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