I need some guidance on Short Ciruit study in OpenDSS. I am a bit new to short circuit study so I would appreciate your patience in reading my long post.
First, I went through the online manual and a few posts in the forum and tried it myself. I took the IEEE 13 bus circuit and just added a few lines at the end to get some exports.
Considering the differences in fault currents for almost every buses in "ALL-Node Fault Currents" in text1, the 3-Phase fault is modeled as an unsymmetrical fault. Is my understanding correct?
a. If I compare the fault current value for BUS 650, it is the same for 3-Phase column in csv1(2101896.1 amps) and Node 2 of Bus 650 in "ALL-Node Fault Currents" section in text1 . So is it fair to say that csv1 shows the max 3-phase fault current across all nodes?
NOTE: The L-L column in csv1 and "Adjacent Node-Node Faults" section in text1 shows a consistent behavior, where the fault current value is the same for Node 2-3 -> 1801817.52 amps vs 1801818 amps.
b. However, for the same bus, it seems that 1-Phase column in csv1(2728212.6 amps) does not match with any of the values in "ONE-Node to ground Faults" section in text1(2810816 amps, 2810904 amps, 2810899 amps). Am I missing something here?
Some other commercial distribution grid tools (eg. CYME, Synergi) report min/max fault current in their short circuit study. However, OpenDSS only reports a single fault current value with FaultStudy. How can we acheive min/max fault current values with OpenDSS? Also what does min/max fault current refer to?
X/R ratio
a. What is the difference between X/R in text1 with X0/R0 and X1/R1 in csv2? "BUS 633" has quite a low X/R in text1 for all nodes compared to X0/R0, X1/R1 in csv2.
b. From planning engineer's perspective which is more useful -> X/R from text1 or X0/R0, X1/R1 from csv2?
I was able to programmatically calculate X0/R0 and X1/R1 via bus properties i.e. Zsc, Zsc0, Zsc1, Zsc012. However, I could not figure out any way to calculate X/R reported in text1. Can you please direct me how to do that?
I have heard some discussions around X/R ratio for 3-phase fault and single line-to-ground fault. How do I obtain those programmatically with the Bus object? I am assuming for symmetrical 3-phase faults we could use Zsc1 -> X1/R1~X/R, right? But how do we calculate it for unsymmetrical fault or single line-to-ground fault?
Is there a reason X/R is not reported for sections "ONE-Node to ground Faults" and "Adjacent Node-Node Faults" sections in text1?
I know I have asked too many questions here but I think the answers to these can help a lot of other folks experimenting with Short Circuit studies in OpenDSS. Thank you.
Last edit: PAnderson 6 days ago
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This was quite a query, but I think I have the answers you need:
Considering the differences in fault currents for almost every buses in "ALL-Node Fault Currents" in text1, the 3-Phase fault is modeled as an unsymmetrical fault. Is my understanding correct?
I would check the fault study mode notes in which Roger back in the day explained the differences between a regular snapshot simulation and fault study. https://opendss.epri.com/FaultStudyMode1.html .
Given the workflow explained at this link, the fault current difference between phases is given to the PCE Y primitive inclusion (loads admittance) in the YBus matrix, which will then introduce imbalance as part of the natural response of the model. For which it is expected to see current imbalance, which will depend on the number of loads connected to it, their number of phases and technical features. If you look at the loads in the IEEE 13 Node test feeder you’ll note that they are mostly single phase.
a. If I compare the fault current value for BUS 650, it is the same for 3-Phase column in csv1(2101896.1 amps) and Node 2 of Bus 650 in "ALL-Node Fault Currents" section in text1 . So is it fair to say that csv1 shows the max 3-phase fault current across all nodes?
NOTE: The L-L column in csv1 and "Adjacent Node-Node Faults" section in text1 shows a consistent behavior, where the fault current value is the same for Node 2-3 -> 1801817.52 amps vs 1801818 amps.
b. However, for the same bus, it seems that 1-Phase column in csv1(2728212.6 amps) does not match with any of the values in "ONE-Node to ground Faults" section in text1(2810816 amps, 2810904 amps, 2810899 amps). Am I missing something here?
Man, this is a long one. Let me start in order: Yes, the 3-phase reported there is the maximum across all the bus phases. The single-phase values are computed based on the 3-phase results; however, it seems that there is a different computation mechanism at the “export” and “show” reports: https://sourceforge.net/p/electricdss/code/HEAD/tree/trunk/Version8/Source/Common/ExportResults.pas#l1523 https://sourceforge.net/p/electricdss/code/HEAD/tree/trunk/Version8/Source/Common/ShowResults.pas#l1670
I think this issue requires further investigation, I’ll look into it and will come up with a solution.
Some other commercial distribution grid tools (eg. CYME, Synergi) report min/max fault current in their short circuit study. However, OpenDSS only reports a single fault current value with FaultStudy. How can we acheive min/max fault current values with OpenDSS? Also what does min/max fault current refer to?
OpenDSS is a general-purpose simulator that provides COM/DLL interfaces for users to customize their simulation experience. There are tools like OpenDSS-G that can generate customized reports for displaying such values. Otherwise, users can always write a simple script using COM/DLL to tailor their reports. In the case of fault study, you can use the bus interface, which provides all the info you need: https://opendss.epri.com/ActiveBus.html .
On X/R ratio:
a. What is the difference between X/R in text1 with X0/R0 and X1/R1 in csv2? "BUS 633" has quite a low X/R in text1 for all nodes compared to X0/R0, X1/R1 in csv2.
b. From planning engineer's perspective which is more useful -> X/R from text1 or X0/R0, X1/R1 from csv2?
Well, it all depends on what you are looking for. Is it imbalance level your priority? Grounding current contribution? Then, I would expect to go with the zero sequence components. Otherwise, Positive sequence should be enough.
I have heard some discussions around X/R ratio for 3-phase fault and single line-to-ground fault. How do I obtain those programmatically with the Bus object? I am assuming for symmetrical 3-phase faults we could use Zsc1 -> X1/R1~X/R, right? But how do we calculate it for unsymmetrical fault or single line-to-ground fault?
You can use the COM/DLL interface as indicated here: https://opendss.epri.com/Zsc0.html
Is there a reason X/R is not reported for sections "ONE-Node to ground Faults" and "Adjacent Node-Node Faults" sections in text1?
Not really, its just that it wasn’t relevant at the time the report was created.
Let me know if this is good enough. If there are doubts or other questions, please come back and we'll look at them together.
Best,
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I need some guidance on Short Ciruit study in OpenDSS. I am a bit new to short circuit study so I would appreciate your patience in reading my long post.
First, I went through the online manual and a few posts in the forum and tried it myself. I took the IEEE 13 bus circuit and just added a few lines at the end to get some exports.
I am posting some sample results below and my questions are at the end.
TEXT1: result of
Show FaultCSV1: result of
export FaultStudy fault.csvCSV2: result of
export SeqZ seqz.csvQUESTIONS:
Fault Current
NOTE: The L-L column in csv1 and "Adjacent Node-Node Faults" section in text1 shows a consistent behavior, where the fault current value is the same for Node 2-3 -> 1801817.52 amps vs 1801818 amps.
b. However, for the same bus, it seems that 1-Phase column in csv1(2728212.6 amps) does not match with any of the values in "ONE-Node to ground Faults" section in text1(2810816 amps, 2810904 amps, 2810899 amps). Am I missing something here?
FaultStudy. How can we acheive min/max fault current values with OpenDSS? Also what does min/max fault current refer to?X/R ratio
b. From planning engineer's perspective which is more useful -> X/R from text1 or X0/R0, X1/R1 from csv2?
Zsc, Zsc0, Zsc1, Zsc012. However, I could not figure out any way to calculate X/R reported in text1. Can you please direct me how to do that?Zsc1->X1/R1~X/R, right? But how do we calculate it for unsymmetrical fault or single line-to-ground fault?I know I have asked too many questions here but I think the answers to these can help a lot of other folks experimenting with Short Circuit studies in OpenDSS. Thank you.
Last edit: PAnderson 6 days ago
Hello,
This was quite a query, but I think I have the answers you need:
I would check the fault study mode notes in which Roger back in the day explained the differences between a regular snapshot simulation and fault study. https://opendss.epri.com/FaultStudyMode1.html .
Given the workflow explained at this link, the fault current difference between phases is given to the PCE Y primitive inclusion (loads admittance) in the YBus matrix, which will then introduce imbalance as part of the natural response of the model. For which it is expected to see current imbalance, which will depend on the number of loads connected to it, their number of phases and technical features. If you look at the loads in the IEEE 13 Node test feeder you’ll note that they are mostly single phase.
NOTE: The L-L column in csv1 and "Adjacent Node-Node Faults" section in text1 shows a consistent behavior, where the fault current value is the same for Node 2-3 -> 1801817.52 amps vs 1801818 amps.
b. However, for the same bus, it seems that 1-Phase column in csv1(2728212.6 amps) does not match with any of the values in "ONE-Node to ground Faults" section in text1(2810816 amps, 2810904 amps, 2810899 amps). Am I missing something here?
Man, this is a long one. Let me start in order: Yes, the 3-phase reported there is the maximum across all the bus phases. The single-phase values are computed based on the 3-phase results; however, it seems that there is a different computation mechanism at the “export” and “show” reports:
https://sourceforge.net/p/electricdss/code/HEAD/tree/trunk/Version8/Source/Common/ExportResults.pas#l1523
https://sourceforge.net/p/electricdss/code/HEAD/tree/trunk/Version8/Source/Common/ShowResults.pas#l1670
I think this issue requires further investigation, I’ll look into it and will come up with a solution.
OpenDSS is a general-purpose simulator that provides COM/DLL interfaces for users to customize their simulation experience. There are tools like OpenDSS-G that can generate customized reports for displaying such values. Otherwise, users can always write a simple script using COM/DLL to tailor their reports. In the case of fault study, you can use the bus interface, which provides all the info you need: https://opendss.epri.com/ActiveBus.html .
On X/R ratio:
b. From planning engineer's perspective which is more useful -> X/R from text1 or X0/R0, X1/R1 from csv2?
Well, it all depends on what you are looking for. Is it imbalance level your priority? Grounding current contribution? Then, I would expect to go with the zero sequence components. Otherwise, Positive sequence should be enough.
Sure, go to: https://sourceforge.net/p/electricdss/code/HEAD/tree/trunk/Version8/Source/Common/ExportResults.pas#l3120
You can use the COM/DLL interface as indicated here: https://opendss.epri.com/Zsc0.html
Not really, its just that it wasn’t relevant at the time the report was created.
Let me know if this is good enough. If there are doubts or other questions, please come back and we'll look at them together.
Best,