Fast restoration of a critical remote load area using a gradual voltage build‐up procedure

Abstract

This study validates an alternative restoration of a critical load area using remote black-start units. Using the conventional restoration, switching actions on a nominal system voltage create switching transients, especially when energising a transformer. The transients maybe close to the resonance frequencies of a weak island system, which may induce high voltages, delay the restoration and damage the equipment in the grid. This study proposes an alternative restoration procedure where, to avoid switching transients, hundreds of kilometres of transmission lines and several transformers are energised using a gradually increasing voltage, which is controlled by the synchronous generator exciter. This study presents detailed procedure flowcharts, a proof of concept for the proposed procedure using a Finnish and an Austrian field tests and theoretical analyses of the tests. The results show that with the gradually increased voltage, harmonic resonances and switching transients during the initial system energisation maybe avoided. In addition, the study shows that variations in the system frequency may cause voltage problems in a weak system during restoration since the system reactance is dependent on the system frequency. Thus, large frequency variations and the unstable operation regions of turbine governors should be avoided during the restoration.