Specific short-circuit conditions in power plants with small generator units

This paper deals with the investigation of generator circuit-breaker applicability in power plants with low rating generator units. The IEEE Std. C37.013 covers round rotor machines only, whereas the generators of the smaller size are often of the salient pole type. The specific short-circuit conditions, such as the presence of delayed current zeros, as well as the transient recovery voltages in these installations are analysed and the results are compared with the performance requirements in the standard. The results show that the short-circuit current ratings of a generator circuit-breaker need to be carefully selected. Moreover, the overvoltages that are generated on fault current interruption require the installation of overvoltage protection means. The main reason for that is the saliency of the generators and considerations of tolerances on its subtransient impedances. However, the usage of conventional overvoltage protections, such as RC filters, allows to meet the requirements in the relevant IEEE standard and particularly of the ones in the new joint IEC 62271-37-013 standard. Therefore additional tests on the circuit-breaker intended for use in such network configurations are not required.