We Need a Power Flow Standard

We do need a power flow standard! This blog describes the issues of concern with regards to the wide variety of power flow packages and why a standard is needed. We also give a first shot at what the standard may incorporate.

What is the power flow?

Ok, if you already know, please skip to the next section. The power flow, also known as load flow, is:

  • the bread-and-butter tool of power system analysts of large and small-scale transmission systems, and of meshed-type distribution circuits.
  • is a set of equations describing the electrical relationships in a power grid. These equations are based on the application of Kirchhoff’s laws to meshed electric networks; to wit, the algebraic sum of all flows into each and every node is equal to zero. If there are n nodes (also known as buses), then there are n complex equations. Solution methods are primarily iterative with the objective of reducing the sum of flows in all nodes to within some acceptably small value known as the mismatch tolerance.
  • is the basis for many market, operations, planning and design decisions and choices affecting power systems.

For more about power flows, especially convergence, heuristics and alternative methods, please see our archives at http://www.pterra.com/index.php/converging-the-power-flow/.

Power Flow Issues

To introduce the topic of issues, allow us to begin with this apocryphal dialogue:

Analyst: “Boss, I finally got the power flow case to converge.”

Supervisor: “Good job, Joe. You followed my advice regarding using (software product #1)?”

Analyst: “Yes, but … I had to go back to (software product #2) after I realized there was a way to tweak it to converge.”

Supervisor: “So, (SP#1) didn’t work?”

Analyst: “Oh, eventually I was also able to get that to solve as well, but I decided to use the results of (SP#2).”

Supervisor: “Eh, why so?”

Analyst: “Well, Boss, the two solutions had different voltages at (Bus 5000). So, I went down the hall to the SOD guys and tried their (Software Product #3). SP#3 gave me a solution closer to SP#2, that’s two out of three SPs, so SP#2’s voltage for (Bus 5000) is right!” Gives a beaming smile.

Supervisor: Scratching head. “I always thought SP#1 was gospel. But, we need to get the results to the design folks. So go ahead and send them what you got. And Joe … make sure you put your name on the report. Good job.”

Although the formulation of and solution methods for power flows are well-defined and described in the literature, for example see papers by Stott and Alsac, Tinney, et al, we often encounter situations of the following form:there are a variety of commercial implementations in current use t