The behaviour of SF6 puffer circuit-breakers

Abstract

The development of transmission power systems and industrial power systems places high-voltage circuit-breakers in operating conditions much more severe than those taken into account by the Standards. Two situations are discussed:

• The case of very long lines for which difficulties encountered upon the energisation and de-energisation of no-load lines and upon shunt reactor switching are reviewed;
• The case of powerful transformers with low impedance voltage whose high natural frequency is at the origin of a severe transient recovery voltage when a fault takes place on the secondary side of the transformer.

In both cases, it is demonstrated that the SF6 puffer circuit-breaker has a satisfactory behaviour though some of the conditions under consideration are exceptionally severe. It is generally unnecessary to resort to the use of auxiliary resistors, except for the energisation of long HV lines.

Introduction

The knowledge of the operation of high-voltage transmission systems and of the phenomena taking place on them upon operation of their protective circuit-breakers has been steadily progressing over the last twenty years. The theoretical study of operating requirements, the analysis of failures and CIGRE work have resulted in the recapitulation of all the conditions which must be taken into account for the design and verification of the switching devices intended to be used in high-voltage power systems. In the end, the process has been materialized by the inclusion of these switching conditions within the scope of international standards whose volume and complexity reflect the extent of the work carried out, a few points being still object of active work.

However, from time to time, special situations not directly referring to the operating conditions covered by the standards may occur. For instance, the extensive application of hydro-electric resources in some countries, necessitating the installation of very long lines, explains why network designers have to define non-standardized conditions for the verification of circuit-breakers. These problems are discussed in the first part of this paper.

Exceptional conditions also affect some installations incorporating powerful transformers with low impedance voltage. These special installations generate heavy stresses for the circuit-breakers; these have not been taken into account in the standards because they differ too much from the severity conditions generally encountered by power system circuit-breakers. This second problem is dealt with in the second part of this paper.

In both cases, the stresses withstood by the circuit-breaker, as well as the test procedures applied to check the satisfactory behaviour of an SF6 puffer circuit-breaker, are reviewed.

AUTHOR: Schneider Electric experts | J.C. HENRY, G. PERRISSIN, C. ROLLIER