Confusion due to IEEE Transactions Paper

Some users have noticed the paper on an open-source Python-based power flow tool called "pandapower" published in the IEEE Transactions on Power Systems November 2018 issue. Some comments were made in the paper about OpenDSS that mischaracterize the program and that has raised some concern among the users. Using the comparisons in the IEEE paper, it is time to revisit some of the unique features of OpenDSS for newer users.

1. Delphi now compiles programs for Linux. The capability comes with the Enterprise version. The Free Pascal Compiler (FPC/Lazarus) has had this capability for a longer time and Tom McDermott has been supporting a Linux version on Sourceforge for some time. I believe an Apple version is also available.

2. In a commercial environment, Delphi is not free like Python, but students and other individuals can obtains a free version of Delphi for the Windows environment that is fully capable of compiling OpenDSS.

3. Many users prefer to work with OpenDSS through Python. This gives the users easy access to the numerous features available in Python while also accessing the speed and power from the natively-compiled OpenDSS program. There are multiple versions of Python interfaces developed by various third parties and made available either through Github or Sourceforge.

4. Version 8 has parallelization built in. It can perform long QSTS simulations exploiting temporaral parallelization. It also has support for Davis Montenegro's A-Diakoptics techniques in which large circuits are torn into several small ones for parallel solution. These features were developed by EPRI with support from Sandia National Labs and NREL.

5. OpenDSS-G, released in 2018, and based on Version 8, also provides a graphical user interface.

6. OpenDSS circuit models are not limited to only 3 phases. The line in the IEEE NEV Test Feeder has 17 coupled conductors in the first pole span. And that is not the limit. In fact there is not a limit on the number of conductors.

7. OpenDSS has the typical 2-winding and 3-winding transformer models used in power system analysis, but there is actually no limit to how many windings a transformer may have. 4-winding transformers are common. Special simulations with more than 40 windings have been performed. The key is obtaining the short circuit impedances between each pair of windings. Single-phase transformers may be combined to create nearly any winding configuration imagineable. The AutoTransformer element was introduced in 2019 in support of the GIC harmonics analysis.

8. Studies of higher-phase-order systems with 6-phase sources, lines, transformers, and reactors have been conducted. Not sure what the limit is, if any.

9. OpenDSS has been able to model ideal switches since it was first created in 1997. Each conductor in each multiphase terminal has a built-in switch that may be opened or closed. Non-ideal switches of microohms upto milliohms may be added like any other branch if desired, but it is often not necessary. Relay, Recloser, and Fuse objects are Control elements that open and close terminals of some circuit element.

10. OpenDSS does not use the per unit system in its internal circuit model. All values are in actual volts, amperes, and Siemens. A nodal admittance circuit model is used because the Y matrix is sparse and the equation I = YV may be solved efficiently by readily-available sparse solvers. Input data and results may be reported in per unit values if the base voltages at the buses are defined.

11. OpenDSS does not use symmetrical component models in its solution. Values may be reported in positive, negative, and zero-sequence values if requested. Line impedances may be specified in symmetrical component values. This is frequently all that is available, although OpenDSS would prefer the unbalanced R, X, and C matrices (which it computes anyway).

12. For most passive elements in the power system, the positive- and negative-sequence impedances are equal (impedance matrices are symmetrical). Generators are the exception where the negative sequence impedance is generally less. Besides Generator models, the Vsource and Reactor models can handle this kind of model where the impedance matrix is anti-symmetrical.

13. One concept that is different about OpenDSS is that there are no special buses. Buses are simply collections of Nodes where conductors from the circuit elements are connected together. This is quite similar to the concept in EMT programs. Buses do not have to be pre-defined by the user. OpenDSS reads the bus names from the circuit element descriptions. In fact, bus objects are not actually instantiated until the first solution is performed.

14. Network harmonics analysis is a native capability of OpenDSS. Loads, Generators, and PVSystems all have default harmonics spectrum object assigned.

15. You can apply a Fault during a power flow solution and a converged solution can generally be achieved.

16. OpenDSS has had Dynamics mode solution capability (electromechanical transients) since 1997. The InductionMachine example provided with the program demonstrates this capability well, include protective device operation (multifunction Relay and a Recloser).