IEEE Std 3002.2-2018 pdf download – IEEE Recommended Practice for Conducting Load-Flow Studies and Analysis of Industrial and Commercial Power Systems.
Also, load flow results are very valuable for setting the proper protective devices to avoid nuisance tripping and improve system reliability. In order to perform a load-flow study, full data must be provided about the studied system, including one-line diagram, parameters of transformers, cables and transmission lines, rated values of each equipment, and the real and reactive power for each load. Modern systems may be complex and have many paths or branches over which power can flow. Such systems form networks of series and parallel paths. Electric power flow in these networks divides among the branches until a balance is reached in accordance with Kirchhoff’s laws. There are generally two types of computer load flow programs—those intended for offline planning purposes, and those designed to operate in real-time, actively receiving input from the actual system. Most load flow planning studies use off-line software. On-line, or real-time load flows incorporate data input from the actual networks and can bridge the gap between static/planning network model and the model used by those responsible for actual system operation. Computer programs are also available that provide integrated off-line and real-time solutions for “what if” predictive analysis. Such systems are able to integrate with existing plant Supervisory Control and Data Acquisition (SCADA) systems. Integrated real-time systems can therefore be used as planning and design tools as well as a dispatching tool for the operator. And an additional level of sophistication is possible using so-called “optimal power flow” modeling that applies constraints in the load flow solution to achieve objectives, such as minimum fuel cost, minimum power loss, flat voltage profile, etc.
A load flow calculation determines the state of the power system for a given load and generation distribution. It represents a steady-state condition as if that condition had been held fixed for some time. There are situations in industrial applications where the issues of interest involve how those steady-state conditions change over periods of minutes to hours as a consequence of changes in loading or generation; these applications can be adequately simulated using conventional load flow tools by means of a series of simulations reflecting the pertinent changes. However, this kind of study may also be accomplished by utilizing a time-domain load flow program. On the other hand, concerns about how systems respond in the cycles-to-seconds time frame, perhaps as a consequence of short-circuits or other disturbances, should be addressed using dynamic stability software.