Load Flow Studies
Load flow studies are probably the most common of all power system analysis calculations because of the savings from reduced downtime and operating costs and improved power system utilization.
A load flow study calculates the voltage drop on each feeder, the voltage at each bus, and the power flow and losses in all branch and feeder circuits. Load flow studies determine if system voltages remain within specified limits under normal or emergency operating conditions, and whether equipment such as transformers and conductors are overloaded.
- Load flow studies are commonly used to:
- Optimize component or circuit loading
- Develop practical bus voltage profiles
- Identify real and reactive power flow
- Minimize kW and kVar losses
- Develop equipment specification guidelines
- Identify proper transformer tap settings
The most important information obtained from the load flow analysis is the voltage profile of the system. If voltage varies greatly over the system, large reactive flows will result. This, in turn, will lead to increased real power losses and, in extreme cases, an increased likelihood of voltage collapse. When a particular bus has an unacceptably low voltage, the usual practice is to install capacitor banks in order to provide reactive compensation to the load. Load flow studies are used to determine how much reactive compensation should be applied at a bus, to bring its voltage up to an appropriate level. If new lines (or additional transformers) are to be installed, to reinforce the system, a power flow study will show how it will relieve overloads on adjacent lines. An inefficient or unbalanced load can also cause unpredictable behavior in your localized power grid, increasing the risk of equipment damage and unplanned outages.
A load flow study should be performed during the planning design stages of a power system and when evaluating changes to an existing system.
This evaluation is an optional extension of a Load Flow Study and compares equipment ratings with normal operating conditions. The study will identify underrated equipment and recommend replacements. The NEC requires that all interrupting devices have ratings sufficient for the current which must be interrupted.