Unlike non-variable (VG) generation sources, wind power has a maximum generation limit that changes through time (variability) and this limit is also not known with perfect accuracy at times in the future (uncertainty). These impacts can create challenges for system operators when ensuring enough units will be online to meet reliability requirements, and to schedule the system to maintain a stable system frequency and minimize the imbalance between generation and load. This paper describes a model, the Flexible Energy Scheduling Tool for Integration of Variable generation (FESTIV), that was developed to mimic operator behavior using a combination of security-constrained unit commitment, security-constrained economic dispatch, and automatic generation control programs. New metrics are used to compare reliability in terms of energy imbalance for different systems or different market and operational structures at very high time resolution. Finally, an example application of the tool and results for a test system are shown.