Highlights

Application of Interrupting Devices. The method of calculating system short-circuit currents developed by the AIEE subcommittee on circuit breakers, switches, and fuses consists of determining the highest value of symmetrical short-circuit current for any type of fault as obtained by dividing voltage by subtransient reactance, and assigning multiplying factors according to the basis of rating and speed of operation of the equipment concerned (Transactions pages 877–81). To facilitate the use of this method in the application of circuit breaker, the short-circuit ratings of breakers should be correlated so that a breaker selected for adequate interrupting capacity automatically has ratings adequate for other related requirements (Transactions pages 882–4). Lightning Protection. The combination of overhead ground wires, transformer-mounted arresters, and line entrance gaps that has been found to provide effective protection from direct lightning strokes for high-voltage high-capacity stations usually is not economical for stations on sub-transmission systems where wood insulation is employed throughout; for these a high degree of protection can be achieved by the use of a reactor to compensate for the “turn-up” of the gap. (Transactions pages 898–900).