Atp to Mathcad[1]

ECE 422 Power Systems Analysis Spring 2011

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Using ATP, ATP Analyzer and MathCAD for Protection Studies

Overview

This handout provides instructions for using the ATPDraw model of the Analog Model Power System to perform protection studies. ATPDraw call the ATP simulation engine, which will be used to perform a fault simulation. You can observe instantaneous currents and voltages using PlotXY along with and RMS voltages and currents.

The output data from the simulation will be converted to COMTRADE format using ATP Analyzer. You can also use Analyzer to calculate the sequence components and perform other calculations is you wish to do so.

Finally, if you have access to MathCAD, you have also received a file that postprocesses the COMTRADE output and implements some simplified relay models.

ATPDraw Model

The system described in the exam handout has been modeled in ATPDraw. The line parameters entered in the model are based on measurements on the AMPS, so they will differ slightly from the idealized parameters on the handout. The file is named 525Proj.adp. When you open that project file in ATPDraw you will see the system below.

Avista

100%

Z_SRCBUS1

LOADBUS4

L3

BUS3BUS2

L1

75% L4

BUS7BUS6

L26 83%L2

F150

The T, N, and A blocks represent the transmission line models of the transient network analyzer (TNA). The impedance values are set, but you can change them if you wish.

The source impedance can be changed by double-left-clicking your mouse on the Z_SRC icon. The R and L (really XL) values listed are in Ohms at 60Hz.

The line impedances are changed in the “N” sections of the TNA blocks. You should probably only change the R and L (again L is XL in Ohms). The capacitance values aren’t likely to impact your results.

The intermediate buses, BUS3 and BUS7, are needed on the physical model power system to provide fault points. In this model, you don’t need to worry about them.

The switch between BUS1 and BUS2 can be used to connect the top two lines to the source. If the switch is open, then the lower line and upper line form a radial system with the load at the mid-point. If the switch is closed you have two lines in parallel with a second infeed for the fault current. The switches are open in the base case file included. If you want to do studies with the switch closed, you should double left click on the switch icon. The following dialog box will


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open. Replace the “1” in each of the T-cl entries with a “-1”. This will force the simulation to treat the breakers as closed.

The fault blocks are located at points where you can implement faults. One is at about 75% of the length of the lower line, another is at 83%, another at 100% (at BUS4) and one at 150% (at BUS3). You can move these to other places in the system. The system as sent does not have any faults enabled. To set a fault, you need to double left click the fault block icon for the fault location you want to use. You will see the following dialog box. The numbers in the “VALUE” column are the ones you need to change to create a fault. The help menu for the dialog box will provide an overview of all of the parameters.

The parameters that you will need to change to implement a fault are the “Nxx_GO” values. For example, to do a SLG fault on phase A occuring 50 milliseconds (3 cycles) into the simulation, you should change NA_GO to 0.05. If you want to implement a LL fault between phases B and C occuring 50 milliseconds into the simulation, you should change BC_GO to 0.05. To do a DLG fault from B to C to ground you need to set NB_GO and NC_GO to both turn on. Make sure your turn off any previous faults before you create a new one (set the start time back to a large number (but smaller than the stop time (xx_STP).

I suggest leaving Nx_STP set to beyond the end of the simulation (i.e. the fault will stay on the system). This will make analysis a little easier. The simulation is presently set to run for a total of 200 milliseconds which should be sufficient for most cases.

If you are familiar with ATP, you can replace with with time controlled switches if you are prefer to use them.


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The LEM module shown below is a metering point. The outputs are the instantaneous line-to-neutral voltages, line-to-line voltages, phase current, RMS voltages (true RMS so the non-60Hz components add to the RMS value), RMS currents and instantaneous power.

To run ATP from ATPdraw,

1. Left click on the “ATP” pull down menu

2. Choose “Make Files As” as shown in the figure below.

3. Use the menu to navigate to where you want to have the simulation output data save. The default is a directory under the ATPDraw installation directory. You need to know where this file (which will have a “.PL4” extension) is saved to call it from Analyzer.

4. Then again left click on the “ATP” menu and this time choose “run ATP” or simply press the “F2” key on your keyboard. You should have a Command Prompt window open on your screen that will show the progress of simulation scrolling past. The window will close when the simulation is complete (whether there is an error or not).


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After your simulation is complete, you can view your results with the plotting program that I sent along called PlotXY. The archive I sent you should have it set up so it appears in the “ATP” pulldown menu as well. The menu in the figure above has additional options since I have some other programs on my computer. When the program opens you will see:


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To select a variable for plotting simply left click the mouse on that name and it will appear in the list on the right. If you select the “Plot” button the a new window with the waveforms will show up.

If you prefer to do you analysis of these cases with PlotXY and only look at the instantaneous overcurrent elements that will be sufficient for at least partial extra credit.

Using ATP Analyzer

ATP Analyzer was developed by BPA to make it easier for protection engineers to use ATP simulations (the development of ATPDraw was also supported by BPA for the same reason).

When you open ATP Analyzer you will get an empty window. Choose File New – Main Case Atp.pl4 Import as shown below.

Browse to find the file you wish to open (if you didn’t give any specific directory location for the “Make File As” command in ATPDraw, this will be in the “ATPDraw4/atp/” directory.

When you select the file a set of plots will show up on your screen. These are the first entries of the PL4 file. Select “Done” to close this window.

When you close the window you will see two windows inside the ATPAnalyzer window. Delete the signals in the “Main Case Signal Selections” in the Analog signals list (select one at a time or as a group and then choose “Cut” from the Edit Selections pull down menu or press the delete key on your keyboard). Then replace them with the ones shown in the figure below. If you


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plan to use the enclosed MathCAD file, these need to be in the order shown or you will need to edit the MathCAD file. Entries are selected from the list on the right side by right or left clicking on the desired entry.

If all you want to do is create a COMTRADE file, then the next step is to resample the ATP output file to a more typical rate for a microprocessor relay. Choose “Main Case” “Resample” “Linear Interpolation, All Signals” (either type of interpolation is sufficient for the moment).

Then a dialog box will open. The text box at the bottom of the screen shows the present sampling rate, replace this with 960 (this is 16 samples per 60 Hz cycle). This is a fairly common sampling rate and the MathCAD file is set up for this.

When you click ok a new window will open asking if you want to Low Pass Filter the Data. Check the box to perform the filtering. The window will freeze for a few moments as the filter parameters are calculated and the button “Resample” will become active. Select that button.


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Then you can save the COMTRADE file with the following “File” “Save Selected Main Case Analog Signals As” “Comtrade File” “ASCII Data (C37.111-1999)”. Use the 1999 ASCII format for the COMTRADE to work with the MathCAD file.

The version of PlotXY sent on your CD will also plot waveforms from COMTRADE files.


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If you want to use Analyzer to calculate the Symmetrical Components choose “Analyze” “Evaluate Signal” “Current” “Symmetrical Component Transforms”. You can look at the various options and then plot the waveforms.

Documents

Atp to Mathcad[1]