TABLE OF CONTENTS S.M. Ghufran Ali
This chapter reviews the circuit-breaker designs which are type tested to IEC 60298 and IEC 62271-100 for use on distribution voltages up to 52 kV.
The design and service experience of different types of commercially available circuit-breakers are considered. The chapter also discusses some special switching duties and focuses on aspects which are necessary for the selection of circuit-breakers for various duties: for example, for switching capacitor banks, capacitive and inductive currents, generators, reactors and synchronised switching of transformers with reactors on the secondary side.
A circuit-breaker is an electro-mechanical device which initiates (makes) or interrupts (breaks) the flow of current in a circuit and is used for controlling and protecting the distribution system. It has to be reliable as it may remain dormant in a closed position for a long period and yet, when it receives a trip command signal, it must operate without any hesitation. Depending on its rating, the circuit-breaker has to interrupt currents from as little as 10 A up to its full short-circuit rating which may be 40/50 kA.
From the turn of the century to the early 1970s most of the AC circuit-breakers used oil (bulk or small oil volume - SOV), airbreak and air blast interrupting techniques. These are now obsolete.
Interrupting devices utilising semiconductor technology are being developed and are not yet available commercially at a competitive price.
Since the mid-1960s vacuum and sulphur hexafluoride (SF 6) circuit-breakers have been available.
