Evaluation of System Performance for Load Dispatch Feasibility Under N-1 Generator Contingencies in Day-Ahead Unit Commitment

Day Ahead (DA) Unit Commitment (UC) enhances system preparedness for real-time dispatch. N-1 thermal generator contingencies challenge the reliability of DA UC. This paper proposes a methodology to evaluate the impact of individual generator outages on UC operational cost, reliability, and operating margin of the scheduled DA dispatch plan, aiding better real-time dispatch decisions. System performance is assessed using criticality, robustness, reliability, and operating margin, with the Contingency Margin (CM) as an implementation indicator. The approach identifies robust and weak buses to determine system robustness and criticality. The paper addresses system reliability during contingencies via the Loss Of Load Probability (LOLP) index. Analysis includes three case studies: Base Case, Case 1, and Case 2. The Base Case executes DA UC without n-1 contingencies. Case 1 analyzes n-1 thermal generator contingency-based DA UC with a CM corresponding to a 10% spinning reserve. Weak and robust buses are identified in Case 1. In Case 2(a), 2(b) and 2(c), CM is evaluated with a gradual reduction in spinning reserve from 10% to 8%, then to 5%, and finally to 0%, while executing n-1 generator contingencies for DA UC. System performance is assessed using the proposed parameters and methodology. The Dynamic Programming technique optimizes DA UC, analyzed on the 24-bus, 26-generator IEEE Reliability Test System. Across all cases, DA UC costs range from $774,020 to $895,400 under varying contingencies. Critical generators (IDs 6, 7) and weak buses (Buses 18, 21) are consistently identified. CM improves from 0 MW in Case 2(c) to 310.5 MW in Case 1; LOLP reduces from 0.0501 to 0; and the operating margin increases from –0.0001 to 0.05. Results confirm that the proposed methodology effectively identifies system vulnerabilities and quantifies the impact of reserve levels on dispatch feasibility, emphasizing the importance of incorporating contingency-aware planning in DA UC and reserve allocation strategies. It provides a practical tool for operators to enhance DA UC planning, reserve allocation, and grid resilience under contingency conditions. This work provides insights for system operators and market planners to estimate performance parameters for DA UC, maintaining grid resilience against unexpected generator outages during real-time load dispatch.