Analysis Tools: DC Load Flow

The way to verify if the schematic diagram of the electrical network to be simulated doesn’t contain errors is to test if the program allows us to simulate a DC load flow.

Figure 73: DC load flow simulation

When the DC load flow function is selected from the menu “Simular estudios estáticos técnicos”, the DC load flow window pops up where, among others, the checkbox “MAKE REPORT FILE AFTER CALCULATION” appears which, when selected, the program creates the text file “DCLFFlujoRamas.dat” in the directory “C:\Work\java\version\run\results\” with the result of the flow that circulates through all the lines of the simulated power network. This file is created when the simulation ends. To start the simulation, press the “Calculate” button, if there are no errors the simulation will be successful.

When the simulation ends, it will appear the flow direction on each line of the schematic diagram of the electrical network, and the percentage that this flow has in relation to the line capacity as shown in Figure 74.

Figure 74: Simulation speed control frame

The nominal voltage and the base power of the busbars are shown next to them, besides, the angle with respect to the slack bar is shown.

In addition, the Speed Control window is displayed, which allows controlling the speed at which the arrows representing the load flow advance.

Figure 75: Invalid power flow error message

If when pressing the button to display the power flow, the error shown in Figure 75 appears, then the power flow simulation has not been executed. To avoid this error always run a DC power flow simulation before asking the program to display the flow in the Network Editor.

Errors in the simulation

Errors that may arise, which prevent the proper execution of a DC power flow simulation, are due to the network being incomplete, poorly drawn, or some data has not been entered or is incorrectly entered in some components.

Incomplete network

If a network is incomplete or there are parts of the schematic diagram that are not connected to each other, the error shown in Figure 76 occurs.

Figure 76: Error message due to isolated system

This leads to the system no longer being interconnected and therefore the simulation cannot be performed. Figure 76 shows an error message indicating that there is a subsystem, where the busbar OXIDOS220 is located, that is disconnected from the system.

Note: If you want to simulate an electrical network that has two interconnected systems, then you must simulate each system separately.

To avoid this error, make sure that the lines you take out of service do not divide the interconnected system in your diagram into two independent systems. To enable out-of-service lines, select the “In service” checkbox in the Operation Information section of the properties window of the line.

Incorrectly drawn diagram

Incorrectly connected elements are sources of errors that prevent the execution of a simulation. Figure 77 shows an example where a misconnected line leaves two independent interconnected systems.

Figure 77: Incomplete interconnection due to a misconnected line

To avoid this type of error, before running the simulation, run the View->Connections function from the Ver menu, which displays a report with the possible connection errors.

Missing information

If your schematic diagram does not have any connection errors and all components that are out of service do not produce disconnected subsystems, you may be able to run the DC power flow simulation, unless you have not entered the proper information in your system components.

This is another source of error, which makes it impossible to run a simulation. Figure 78 shows the error message produced indicating that the network to be modeled has originated a singular linear system.

Figure 78: Error message due to missing information in a component

This error occurs mainly because the transformer element has not been given the resistance and reactance values required to model its losses. This causes two busbars of different voltage to be, for simulation purposes, directly connected as a short circuit, thus producing the error shown in Figure 78.

To avoid this error, change the properties of each transformer that needs to be modified. To do this, in the transformer properties window, find the Operation Information (parameters in pu) section and enter the required resistance and reactance values.