Improved Protection Scheme Based on D-q Components for Synchronous Generator

A protection scheme for detecting and classifying internal faults in synchronous generators (SGs) based on the calculation of d-q components of stator currents at neutral and terminal ends is presented in this paper. Detection of internal faults is achieved based on the rate of change of q component of the stator current at the neutral end compared to a pre-defined threshold. Thereafter, discrimination between internal faults and external conditions is obtained by taking the difference of rate of change of q component at the terminal and neutral ends. Subsequently, internal fault classification is carried out based on the rate of change of zero component of the neutral end current. The proposed scheme is validated using various fault cases obtained from a simulation network developed in a real-time digital simulator (RTDS) as well as from an experimental setup of the SG. The proposed scheme can detect all types of internal faults, including inter-turn faults, regardless of the generator winding configuration for low-resistance grounded SGs. It is also capable of distinguishing internal faults from external conditions within a quarter cycle, independent of current transformer errors and saturation, as well as variable loading conditions and SG ratings.