Load Flow Study
A load-flow study determines, if the system voltages are within specified limits under various conditions. Transformers, and conductors are properly loaded and motors have proper operating voltage. Load-flow study often identifies the need for additional generation, capacitive, or inductive VAR support, or the placement of capacitors and/or reactors to maintain system voltages within specified limits.
The Load Flow Study evaluates the adequacy of continuous overload ratings of cables, transformers, and buses. The study also determines anticipated low, or high, voltage levels on various sections of the power system under maximum loading condition of a unit substation transformer.
National Electrical Codes (NFPA70), such as the NEC in the United States, limit the total voltage drop in any one branch or the total bus voltage drop. Thus, it is critical in the design process to know the voltage drop in each branch of the power system, and the total voltage drop from the source of supply to the bus in the branch circuit. The voltage drop calculations are incorporated directly into the calculation of the steady-state load flows. Reasonable operating efficiency is achieved if the voltage-drop of a branch circuit is limited to 3%. However, total voltage drop of a branch circuit plus a feeder circuit can reach 5% and still achieve reasonable operating efficiency.
