In real-time energy market, Regional Transmission Organization (RTO) dispatchers meet the energy demand while respecting transmission security constraints using the least-cost security constrained economic dispatch program, called Unit Dispatch System (UDS). If the transmission violation detected by the Energy Management System (EMS) requires redispatch, system operator will transfer the transmission constraint information to UDS for resolution through a manual process. Dispatchers need to make an educated guess on constraint trends to support their manual redispatch process. However, as the number of constraints increases during peak hours, this process is more and more complicated and the system becomes less manageable. This paper intends to challenge this operational difficulty through a similarity model to reveal the constraint relations and a heuristic pattern recognition method to categorize constraints into controllable constraint groups (CCG). System operators only take care of a dominant constraint in each CCG using controllable units instead of them all. This will make system much more manageable during peak hours, therefore, will increase effectiveness and efficiency of system operations.