Speeding Up PSS/E Transient Stability Studies of Power Systems with EnFuzion

Speeding Up PSS/E Transient Stability Studies of Power Systems with EnFuzion

Summary
This application note demonstrates how to dramatically reduce the time required to perform a PSS/E transient stability analysis of power line faults by using multiple computers and EnFuzion.

The study in this note simulates a fault in a transmission line. The goal of the study is to find the critical clearing time, which is the shortest fault duration at which the system fails to re-synchronize after the fault. The solution methodology is to calculate many cases with different fault durations.

By using EnFuzion, all these cases are easily executed concurrently on multiple computers. This significantly reduces the calculation time and makes it feasible to do more thorough studies, ultimately leading to a better system understanding and more reliable power delivery.

The methodology used in this demonstration is also useful for other types of power systems transient and dynamic stability analyses.

What is Power System Simulator for Engineering (PSS/E)?
Power System Simulator for Engineering is an integrated, interactive program from Shaw Power Technologies Inc. (PTI) for simulating, analyzing and optimizing power system performance. It makes available to the user analytical methods for studying many power system phenomena, including: power flow, fault analysis, dynamic simulation, open access and pricing, transfer limit analysis and network reduction.

How Does EnFuzion Speed Up PSS/E Simulations?
EnFuzion helps with PSS/E simulations in many ways. It schedules execution of multiple PSS/E simulations on all available computers. By distributing execution over multiple computers, the results are obtained faster or more simulations can be performed in the same time period. Additional EnFuzion benefits include optimum resource utilization and reliable execution by working around computer failures. This maximizes engineer's productivity by handling all aspects of job scheduling.

How Is EnFuzion Used With PSS/E?
This note shows in detail how a PSS/E fault analysis, which consists of several cases, is executed faster using multiple computers.

In this example, a fault is placed on a power line. The duration of the fault is varied from a few cycles to several tens of cycles. This produces several "cases", with each case representing a different fault duration. The results of these cases are compared to determine the ability of the system to re-synchronize after the fault, and to determine the maximum fault duration for which the system can be re-synchronized.

Axceleon thanks PTI for providing the input example. This sample data presents a realistic demonstration of the capabilities of the EnFuzion when using PSS/E. The data is not intended to be a demonstration of PSS/E capabilities.

The example is executed as follows:

download input files for the example, which are available here, and extract them to a directory,
install EnFuzion on the local computer,
install PSS/E and EnFuzion on all computers that will be used to execute PSS/E jobs,
configure EnFuzion by specifying remote computers in file c:\enfuzion\config\enfuzion.nodes on the local machine,
if PSS/E on remote machines is not installed in its default directory c:\Program Files\PTI\PSSE29, then modify the set Path statement in ds.pln,
specify the parameter range by clicking on ds.pln. Type parameter values in the form and save them by selecting File:Save Run. This produces file ds.run, which contains a description of jobs and is executed in the next step,
execute jobs by clicking on ds.run. This starts job execution on all remote computers. A text window shows an execution log and progress.

How Does the Example Work?
The PSS/E simulation consists of the following input files:

bench2.sav, a PSS/E input file,
bench2.snp, a PSS/E input file,
ds-template.idv, a PSS/E input template for the study.

Results are stored in multiple output files. Each file represents one fault analysis and is in the form of bench-<nn>.OUT, where <nn> is the fault duration.

The process of executing the dynamic stability analysis on multiple systems is performed as follows. The user selects the range for the fault duration from the shortest fault to the longest fault, which generates one job per fault duration. EnFuzion takes all the jobs, executes them on all available computers, and collects the results to output files.

Detailed execution steps are as follows:

initialization of remote computers:
- input files that are common to all jobs, are copied from the root computer to each node computer that participates in the execution of jobs. These files are bench2.sav, bench2.snp, and ds-template.idv.
This step is performed once on each remote node computer before it starts executing the PSS/E simulations.
execution of jobs:
- for each job, parameters cycle and time in the input template file ds-template.idv are replaced with specific values for the job,
- a single SS/E simulation is executed with job specific parameters, corresponding to one fault duration,
- results from the PSS/E job in file bench.OUT are copied from the node computer to the file bench-<nn>.OUT on the root computer. <nn> is replaced with the number of cycles for that job.
This step is performed once for each job on the remote node computer that is executing this job.

The steps above are described in a plan file ds.pln, which provides EnFuzion with commands to execute for each of the steps.

The entire EnFuzion plan file to execute the dynamic stability study is as follows:

    # set the PATH variable. Modify the value to match your node systems.
    set Path "C:\\PROGRA~1\\PTI\\PSSE29\\PSSEXE;C:\\PROGRA~1\\PTI\\PSSE29\\PSSBI
    N;C:\\PROGRA~1\\PTI\\PSSE29\\PSSLIB;C:\\PROGRA~1\\PTI\\PSSE29\\PSSIPL;C:\\WI
    NNT\\system32;C:\\WINNT;C:\\WINNT\\System32\\Wbem;";

    # specify range for the cycles parameter
    parameter cycles integer range from 4 to 20 step 1;

    # calculate the simulation time, which is the fault duration plus 0.1s
    parameter time float compute 0.1+(cycles)/(60.0);

    # node initialization, copy common files to a remote computer
    task nodestart
        copy bench2.snp node:.
        copy bench2.sav node:.
        copy ds-template.idv node:.
    endtask

    # job execution:
    #     - substitute parameter values in the PSS/E command file
    #     - execute PSS/E
    #     - copy back the result file
    task main
        node:substitute ds-template.idv ds-input.idv
        node:execute  pssds4 -gnikool off -inpdev ds-input.idv
        copy  node:bench.OUT bench-$cycles.OUT
    endtask

The EnFuzion plan file consists of the following:

set Path sets the Path variable on the remote node. This example uses default PSS/E values. If PSS/E in your installation is installed in a different directory, change the line to match your installation.
parameter cycles is the main variable for the study. It specifies the fault duration range in cycles. The plan file contains the default values, which can be changed before the study is executed.
parameter time is the simulation time. The simulation is the sum of the fault duration and an additional 0.1 s interval.
task nodestart copies common input files to each remote computer. These files are bench2.snp, bench2.sav, and ds-template.idv. bench2.snp and bench2.sav provide input data for the study, ds-template.idv contains PSS/E commands to execute the simulation.
task main substitutes parameter values in the PSS/E command file, executes the simulation and returns the result.

How Is the Example Executed?
The plan file ds.pln is executed as follows:

specify the range for the fault duration by clicking on ds.pln to bring up a window. Change the from, to, and step values for your study. Select File:Save Run from the menu to save values. This creates ds.run.
execute jobs by clicking on ds.run. This starts job execution on all remote computers. A text window shows an execution log and progress.

While the program is running, a Web based interface is available at http://<hostname>:10101. Replace <hostname> with the name of the EnFuzion Root computer.

Further information
This application note describes how EnFuzion is being used with PSS/E from Shaw Power Technologies Inc. to speed up a dynamic stability study. It uses EnFuzion 8 release and PSS/E Version 29. You can find out more about the use of EnFuzion for power utilities on the Axceleon Web site at www.axceleon.com.

Axceleon thanks PTI for feedback and assistance with the note. You can find out more about PSS/E at http://www.shawgrp.com/PTI/software/psse/index.cfm.