The UFLS Review Group recommends that the impacts of rapid and widespread losses of local generation during frequency excursions due to DG tripping be a primary focus next study cycle. Study: Northern Island Northern Island: Approach Load/generation imbalance scenarios were based on the post-separation load levels in the northern island. As shown in the previous tables, the northern island load was 80,369 MW in the summer case and 73,524 MW in the spring. Five imbalance scenarios were studied. Table 13 shows the minimum amount of generation to be tripped to accomplish each load/generation imbalance target. Groups of generators were selected and taken out of service so that the aggregate loss of generation was close to the imbalance scenario targets. The imbalance scenario targets were based on connected load rather than connected generation. This approach is consistent with the original WECC Plan design methodology. Table 13: Imbalance scenario targets. The criteria for selecting which generators to trip were arbitrary. Nevertheless, an attempt was made to minimize the number of units being tripped, thereby reducing the number of concurrent contingencies required for such an event. Larger units were selected with some smaller units to keep the total loss near the imbalance targets. Units that showed a propensity for going unstable were tripped as well, with the conservative assumption that these units would self-protect during an event anyway. Several generator units exhibited instability, likely because of either improper governor or exciter models. This was indicated by unrealistic VAr outputs or local frequency. A list of models that failed within the first 20 seconds of the simulations is in Appendix L. Table 14 and Table 15 show summaries of the amount of generation tripped, by area, for each imbalance scenario. Table 14: Total generation tripped, by area, for 2017 heavy summer northern island simulations. Table 15: Total generation tripped, by area, for 2017 heavy spring northern island simulations.
The UFLS Review Group recommends that the impacts of rapid and widespread losses of local generation during frequency excursions due to DG tripping be a primary focus next study cycle. Study: Northern Island Northern Island: Approach Load/generation imbalance scenarios were based on the post-separation load levels in the northern island. As shown in the previous tables, the northern island load was 80,369 MW in the summer case and 73,524 MW in the spring. Five imbalance scenarios were studied. Table 13 shows the minimum amount of generation to be tripped to accomplish each load/generation imbalance target. Groups of generators were selected and taken out of service so that the aggregate loss of generation was close to the imbalance scenario targets. The imbalance scenario targets were based on connected load rather than connected generation. This approach is consistent with the original WECC Plan design methodology. Table 13: Imbalance scenario targets. The criteria for selecting which generators to trip were arbitrary. Nevertheless, an attempt was made to minimize the number of units being tripped, thereby reducing the number of concurrent contingencies required for such an event. Larger units were selected with some smaller units to keep the total loss near the imbalance targets. Units that showed a propensity for going unstable were tripped as well, with the conservative assumption that these units would self-protect during an event anyway. Several generator units exhibited instability, likely because of either improper governor or exciter models. This was indicated by unrealistic VAr outputs or local frequency. A list of models that failed within the first 20 seconds of the simulations is in Appendix L. Table 14 and Table 15 show summaries of the amount of generation tripped, by area, for each imbalance scenario. Table 14: Total generation tripped, by area, for 2017 heavy summer northern island simulations. Table 15: Total generation tripped, by area, for 2017 heavy spring northern island simulations.
2017_ufls_report_2_13_2018_clean.docx