NetSimIntroductory Examples2NetSimArticle Number VESD4006 - Manual Version: NETSIM.ENU.8 - Year: 2014 OMICRON electronics. All rights reserved.This manual is a publication of OMICRON electronics GmbH.All rights including translation reserved. Reproduction of any kind, for example, photocopying, microfilming, optical character recognition and/or storage in electronic data processing systems, requires the explicit consent of OMICRON electronics. Reprinting, wholly or in part, is not permitted. The product information, specifications, and technical data embodied in this manual represent the technical status at the time of writing and are subject to change without prior notice.We have done our best to ensure that the information given in this manual is useful, accurate, up-to-date and reliable. However, OMICRON electronics does not assume responsibility for any inaccuracies which may be present.The user is responsible for every application that makes use of an OMICRON product.OMICRON electronics translates this manual from the source language English into a number of other languages. Any translation of this manual is done for local requirements, and in the event of a dispute between the English and a non-English version, the English version of this manual shall govern. Table of Contents3Table of Contents1 NetSim Introductory Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 Earth Fault in Phase A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92.1 Starting NetSim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112.2 Entering the Source Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112.3 Entering the Fault Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122.4 Running the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122.5 Results and Time Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133 Earth Fault Near the Circuit Breaker in a Single Feeder Configuration . . . .153.1 Entering the Fault Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163.2 Entering the CB Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173.3 Entering Time Assessment Conditions. . . . . . . . . . . . . . . . . . . . . . . .183.4 Running the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183.5 Results and Time Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194 Fault with Autoreclosure and Persisting Fault . . . . . . . . . . . . . . . . . . . . . . . .214.1 Entering the Output Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.2 Entering the Circuit Breaker Parameters. . . . . . . . . . . . . . . . . . . . . .234.2.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .234.2.2 Timing for the Initial Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .244.2.3 Entering the Timing for the Reclosure and the Persisting Fault. . . . . . .254.2.4 Entering Time Assessment Conditions . . . . . . . . . . . . . . . . . . . . . . . . . .264.3 Running the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264.4 Results and Time Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264OMICRON Test Universe5 Multiple Faults on Parallel Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275.1 Selecting the Network Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 285.2 Entering the Source Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285.3 Entering the Line Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295.4 Entering the Fault Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305.5 Entering the CB Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.6 Running the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325.7 Appendix - Mutual Coupling Impedance. . . . . . . . . . . . . . . . . . . . . . . 356 Testing Power Swing Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.1 Selecting the Test Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.2 Entering the Source Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.3 Entering the Fault Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.4 Setting up a Sequence of Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406.5 Setting up a Time Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416.6 Running the Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 Considering CT Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Power Transformer Test Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515Introductory Examples1Introductory ExamplesIntroductionNetSim Introductory Examples is a collection of test case examples, which are intended to give the user a quick start into OMICRONs Network Simulation test module. This collection of examples is neither a complete functional reference, nor a detailed user manual. The application of NetSim is explained by performing and mastering the NetSim examples. The most important features of the module will be covered; the individual settings that depend on the users network will be omitted.Reference information about the test modules is found in the module-specific Help. You are encouraged to use this reference first whenever you have a question or need further explanation about a specific topic.Although NetSim is easy to use even for users who have never worked with network simulation before, it is an advanced test module and it is targeted for advanced users. This manual assumes that the user has previous experience with other OMICRON test modules, for example State Sequencer, and has the understanding of OMICRON Test Universe concept. The common basic tasks for all test modules, like setting nominal values in a Test Object, routing of input and output signals in the Hardware Configuration or changing the Report Settings are not explained in this manual.About NetSimThe Network Simulation (NetSim) simulates events in an electric power supply network. NetSim can generate the corresponding secondary voltages and the secondary currents from distinct locations in the network via a connected CMC test set. These voltage and currents represent close to realistic conditions to a connected relay. This relays response to this stimulus can then be measured and evaluated.NetSim uses a numerical model to calculate the quantities and to simulate a power system. The power system is composed of voltage sources, lines, and circuit breakers. The fault instances and the switching events determine the changes and the actions in the network.NetSim provides predefined Test Cases and Network Configurations. The test cases define the type of event to be simulated and the network configurations determine the topology to be used for the simulation. Further test cases and network configurations can be added to NetSim later on.6NetSimNetSim provides a choice of pre-defined test cases and network configurations. The only required user interaction is to enter the applicable specific parameters to specify the network configuration and the fault instances, and to eventually run the test.The user interface of NetSim is composed of several views: the Test View, the Time Signal View, the Time Assessment, the Impedance View, and the Report View.Test ViewThe Test View contains the complete specifications for the simulation that is performed. The parameters are grouped into several tabs. A graphical representation of the actual network configuration with some important labels is displayed to provide a reference for the parameters in the tabs. All parameters are preset with a default value. You can immediately run a simulation with these defaults.Figure 1-1:Test View with graphical representation of network configurationWith regard to the network parameter tabs described below, please bear in mind that if secondary values are being displayed, the ratio of the according selected reference location Bneeds to be considered! 7Introductory ExamplesIf in doubt, insert the network parameters as primary values.The Fault tab: Specifies the parameters for the fault(s). Durations for the prefault, fault and postfault Fault parameters, for example, type, location, inception angle and resistance for short circuit faults.The Lines tab: Specifies the parameters for the line (impedances). Method of specifying the line impedances Sequence impedances, line length and relative length of segments.The Sources tab: Specifies the parameters for the sources (generators). Frequency, voltages, phase shifts and source impedances.The Outputs tab: Displays the CMC test set's analog current and/or voltage outputs that are used for calculation when simulating the selected test case as well as the assignment of the test set's binary outputs to Simulation events and their specified delay times.The CB tab: Specifies the circuit breaker actions. Initial states of the CBs at the fault inception Changes of the CB states (open / closed) after the fault inception.The General tab: Specifies the condition for starting the playback of the signals with the test set. The playback starts immediately without any condition after the simulation and the download of the data. On an external event, for example, pressing a key, activating a binary input or receiving a synchronization signal from a GPS receiver.The Sequence tab: Specifies multiple simulations with different settings and complete series of simulations with varying parameters. One or two parameters, which can be varied Multiple parameter settings for simulations and automatic setups of complete series.Time Signal ViewThe Time Signal View is the main view for analyzing the simulated waveforms and for in-depth analysis of the test resultsThis view is constantly updated to provide a preview of the calculated signals during the test setup, for example, parameter input in the Test View.8NetSimAfter a test, this view also shows the status of the recorded binary inputs during playback, along with the generated voltages and the generated currents. The detailed evaluation of the instantaneous values and of the time relationships are provided by using the cursors.Time AssessmentAt Time Assessment set up measurement conditions and displays the actual values and the automatic assessment of the results after a test. The usage of the NetSim Time Assessment is identical to the one in the State Sequencer and Advanced Transplay test modules.Impedance ViewContrary to the Time Signal View that displays the voltages, currents and the resulting fault impedance along a time axis, the Impedance View displays the fault impedance in the complex plane, taking into consideration the zone characteristic settings made at the Distance Test Object (Mho, Lens/Tomato or polygonal).The number of diagrams displayed in the Impedance View depends on the selected test case and the resulting number of measurement locations. The Impedance View always displays the impedance curves of all measurement locations of a particular test case.At Display Impedances set whether you want to display for each measurement location: one individual impedance per diagram (for example, ZAL1, ZAL2, ZAL3 ...), or the impedances of a triple (3 lines) per diagram (for example, ZAL1-E + ZAL2-E + ZAL3-E ...); A being the designation of the measurement location. In addition, set whether it is a line to ground (L-E) or a line to line (L-L) fault. For line to ground faults, the k-factor set in the Distance Test Object is taken into consideration.Select the Show measurement points options to display the measurement points along the impedance curve (measurements in fixed 0.2 ms time intervals).Report ViewThe Report View displays a preview of the report with the settings for the simulations and results of the test. The NetSim Report View is identical to the Report View in the other OMICRON test modules.9Earth Fault in Phase A2Earth Fault in Phase ATaskTo investigate an earth fault on a single line.For this example, the dynamic behavior of voltages and currents during a single-phase fault, occurring on a single line, are observed. The quantities are measured on the busbars. SolutionThe test case used for the example is shown in the following figure:Figure 2-1:Test case for short-circuit event simulationThe testers job is to simulate a single-phase fault on phase A, at 80 % of the line length between the two relays during nominal power transfer.A prefault current is attained by a suited setting of either the voltage magnitudes or the phase angles of the sources, or a combination of both. For this test, the phase of source 2 will be adjusted accordingly.Note: All values are specified in secondary values.Source 1Line 1 Line 2 Line 3Source 280 %10NetSimThe default settings for the line impedance and source impedance are used in this example. They are:For source 2, U2 = 100 V36 is chosen. During the faultless period, this causes a current of:Figure 2-2:Calculation of the current during the faultless period Z1,Line: 3 85 Z0,Line: 12 85 Z1,Source: 15 85 Z0,Source: 54 85 Fault location: 0.8 p.u. of line 2 Line 1, Line 2: 0.5 p.u. of line 2 Z2 = Z1 U1 = 100 V 0 = = + = 13 99 . 085 3672 7 . 352 23 3, 1 , 12 1AVZ ZV VISource LineSource SourcePrefault11Earth Fault in Phase A2.1Starting NetSimNetSim loads the default values for the test case. In this example, the test is performed using the default parameters and the given default values. For this reason, only the settings that differ from the defaults are explained below; dialogs that require no changes for this example are omitted but are subsequently explained as needed.Figure 2-1: Test case for short-circuit event simulation on page 9 represents the default test case.Start NetSim from the Test Universe start screen by clicking "Network Simulation...", and then "NetSim".2.2Entering the Source ParametersSetting Delta phi changes the phase angle for source 2 to -36 to provide the desired prefault current as calculated in Figure 2-2: Calculation of the current during the faultless period on page 10.To enter the source parameters, proceed as follows:1. In the NetSim Test View, click the Sources tab.2. In the Delta phi box type in -36.00 to change the phase angle for source 2. Figure 2-3:Source parameters: the phase angle for source 2 is shifted to -36 12NetSim2.3Entering the Fault ParametersThe Fault parameters are set to 80 % by entering a value of 0.8 p.u. for the Fault location. This value of 0.8 p.u. permits the fault event to start after the prefault time has elapsed, and also permits the reference phase to meet the inception angle after its next positive zero crossing.To enter the fault parameters:1. In the NetSim Test View, click the Fault tab.2. In the Fault location box type in 0.8 p.u. to set the fault location to 80 %.Figure 2-4:Fault parameters: the fault location is set to 80 % of line 22.4Running the TestDuring the setup of the test, the preview data are constantly updated after any change of a parameter value. For a real test with a signal output via a CMC test set, the test must be directly started from the Control Center. The signals must be routed to distinct outputs of the test set.To run a single test click Single Test on the Home tab.13Earth Fault in Phase A2.5Results and Time SignalsThe Progress bar at the bottom of the window provides information about the performance of the test. First the simulation itself takes place, then the transient data are downloaded into the test set, and finally the signal output is performed. The distribution of the time for the whole test progress depends very much on the available processing power and the type of simulated event. A typical distribution at the time for the test could be 50 % for the simulation, 40 % for the download, and 10 % for the signal output.For a real test with a connected test set, the calculation of the quantities is done with a higher accuracy than during the offline mode. Therefore, a sampling frequency of 5 kHz is used instead of only 1 kHz for the preview in the Time Signal View.The quantities are shown in matching triples and are measured by using the cursors.Figure 2-5:Time Signal View of simulated quantitiesThe "plausibility check" of the voltages and the currents in figure 2-5 results in a positive assessment. The voltage in phase A breaks down into smaller values during the fault. Since the fault is closer to phase B, the voltage is smaller in phase B than in phase A. The voltages in the healthy phase of B and C rise due to the displacement of the neutral point.The current in phase A rises but the currents in the healthy phases B and C do not change during the fault. The peak value is about three times the prefault value immediately after fault inception. After approximately 130 ms, the DC component decays and the steady state short-circuit current is roughly twice the prefault current.14NetSim15Earth Fault Near the Circuit Breaker in a Single Feeder Configuration3Earth Fault Near the Circuit Breaker in a Single Feeder ConfigurationTaskTo investigate a close-in fault on a spur line. Although NetSim does not provide a test case that specifically models this case, this can be easily accomplished by providing appropriate settings for the circuit breakers so that the second source is disconnected from the beginning of the simulation.The testers job is to perform an automatic assessment of the trip time of the protection relay. For this example, a measurement is set up to measure the time between the fault incident and the trip signal from the relay.SolutionThe same fault event (short-circuit) and the same test case (single line) used in Example 1 are also used for this test. Again, this is the default test case when starting NetSim.Figure 3-1:Test case for short-circuit simulation with disconnected source 2For this example, the default settings can be used except for:Since the example contains a spur line with no load, no current will flow through the faultless periods. The steady state fault current can be calculated from the formula for a single-phase fault.Figure 3-2:Calculations of the steady state fault current for a single-phase faultNote: These equations can be used to verify the simulation. Fault location = 0.1 p.u. of line 2 Length of Line 1 = 0.5 p.u. of line 2Source 1Line 1 Line 210 % = = + + + =+ + = 85 83 . 185 8 . 940 2 . 1732 2 . 1 6 . 03 33, 1 , 1 , 0 , 012 1 01AVZ Z Z ZVZ Z ZVISource Line Source LineSource SourceFault16NetSim3.1Entering the Fault ParametersSetting the Fault location in the Fault tab to 0.1 p.u. of line 2 simulates the fault close to Bus A.To enter the fault parameters:1. In the NetSim Test View, click the Fault tab.2. In the Fault location box type the 0.1 p.u.Figure 3-3:Fault parameters: the fault location is set to 10 % of line 217Earth Fault Near the Circuit Breaker in a Single Feeder Configuration3.2Entering the CB ParametersChanging the circuit breaker (CB) parameters causes the disconnection of Bus B for the entire simulation. This simulates the existence of a spur line.Note: Changing the CB B parameter from Closed to Open is necessary to cause the disconnection of Bus B.To enter the CB parameters:1. In the NetSim Test View, click the CB tab.2. At Initial state, select Open for CB B.Note: Leave the default values for all the other settings of the loaded configuration on the CB tab.Figure 3-4:CB Parameters: set the CB B parameter to Open18NetSim3.3Entering Time Assessment ConditionsTo perform an automatic assessment of the test result, define the nominal behavior at Time Assessments.The nominal value for the trip time of the relay is specified as 400 ms 50 ms. The measurement condition is named CB-off and ignores any events occurring before the Fault event. Time measurement starts with the Fault event and ends with the trip signal changing from 0 to 1. The measured actual time Tact is compared against the boundaries given by Tnom, Tdev+ and Tdev- to obtain the assessment.Figure 3-5:Time Assessments definition3.4Running the TestThe performance of a protection relay on Bus A is tested by injecting the simulated voltages and the simulated currents and by reading back the trip signal with a CMC test set.To run a single test click Single Test on the Home tab.After the test, the measurement condition is updated with the actual trip time and the assessment.Note: With the parameters used in this example, the measured trip time lies well inside the tolerance boundaries. Therefore the assessment is passed.Figure 3-6:Time Assessments results19Earth Fault Near the Circuit Breaker in a Single Feeder Configuration3.5Results and Time Signals The calculated voltages and calculated currents are shown in the Time Signal View.The voltages and the currents show the typical shapes of those quantities during a single-phase fault. With the cursors, it is easy to measure the peak value of the steady state of current, which is slightly more then 2.5A. This steady state of current matches the current as calculated in figure 3-2 on page 15.Figure 3-7:Time Signal View with transient fault quantities and measured trip signals20NetSim21Fault with Autoreclosure and Persisting Fault4Fault with Autoreclosure and Persisting FaultTaskTo simulate a typical sequence of a failure event and an autoreclosure cycle. The fault is assumed to be persistent, and the autoreclosure will be unsuccessful.SolutionA reasonable simulation of such a course of events is possible even though NetSim is not a real-time simulation tool, and therefore cannot take into account the reactions of the relay being tested for the actual signal calculations.Two circumstances can be used to support the solution:1. For the relay being tested, reasonable signals with causal timing have to be provided. Since the circuit breaker has some action time, the relay does not require the fault condition to disappear immediately after the trip so it is appropriate to set up the test sequence in such a way that the fault is cleared in a practical time.2. Similar considerations apply for the reclosure time and the clearing of the persisting fault. Since the pause time runs from the moment the clearing of the fault is detected until the reclosure signal is issued by the relay, the drop-off time, the pause time and the CB-close time have to be included into the calculations. The timing for the persisting fault corresponds to the explanation above.The CB tab in the NetSim Test View provides the necessary settings to configure the appropriate sequences for this example.All other settings for the source and fault parameters are identical to Earth Fault in Phase A on page 9. Please refer to Entering the Source Parameters on page 11 and Entering the Fault Parameters on page 12 for further information.22NetSim4.1Entering the Output SettingsPTs connected to the busbar is the output setting for this example. This setting will deliver a faster pick-up of the persisting fault for some relays.Selecting the other output setting instead (PTs connected to the line) may increase the trip time for the persisting fault. This is because there is no voltage present during the pause time and the relay does not obtain useful prefault information. You can easily investigate this effect by changing the PT connection settings.Figure 4-1:Output tab: settings for PTs connected to the busbar23Fault with Autoreclosure and Persisting Fault4.2Entering the Circuit Breaker Parameters4.2.1GeneralThe CB tab in the NetSim Test View provides the means to define the circuit breaker (CB) actions during the course of the simulation.Figure 4-2:CB tab: default initial states and state changesAt the start of the simulation, the initial states of the CBs are defined at Initial State on the CB tab. The Initial State feature has been previously used in Entering the CB Parameters on page 17 for simulating the spur line by disconnecting busbar B.The settings for changing the state of the CBs can be made at Circuit Breaker A and Circuit Breaker B. Per CB you can define up to four state changes. The timing of the state changes refers to the fault event. Settings for three-pole and single-pole openings and for three-pole closing of the CB are provided.Changes in the CB states are defined from top to bottom so any unused fields remain in the (unchanged) default setting.Note: For other test cases with more CBs, for example, double line, additional CB tabs will be available in the Test View.24NetSim4.2.2Timing for the Initial FaultThe following times are assumed: A trip time of approximately 30 ms with a pick-up and instantaneous trip for the relay. An opening time of approximately 50 ms for the CB.So, for this example, the CB states are set to "open" at 80 ms after the Fault event.For the relay, this setting makes it look as if the CB "opened" on its trip time. One condition for the causal timing is that the fault leads to an instantaneous trip of the relay, that is, it is a zone 1 fault for a distance relay.25Fault with Autoreclosure and Persisting Fault4.2.3Entering the Timing for the Reclosure and the Persisting FaultFor the reclosure and the persisting fault settings, the following times are assumed: a drop-off time of approximately 30 ms for the relay a pause time of 200 ms until the reclosure command is issued a closing time of approximately 50 ms for the CB a trip time of approximately 30 ms for the persisting fault an opening time of approximately 50 ms for the CB.Since the drop-off is counted from the fault clearance, which is the first "CB open" event, the state of the CBs is changed to "closed" after (80 + 30 + 200 + 50) ms = 360 ms. At this moment, the fault persists.80 ms later, after the second trip and the CB opening, the CBs are set to "open" after the fault event because the relay will trip again due to the persisting fault.Figure 4-3:CB settings for fault sequence with reclosure and persisting fault26NetSim4.2.4Entering Time Assessment ConditionsThe time assessment conditions are set for the measurement and the assessment of the trip time.Measuring the second trip, for example, the persisting fault, is not possible since the condition would be the same as for the first trip, that is, the initial fault. Therefore the measurement would again deliver the first trip time.Figure 4-4:Time assessment conditions for trip time and pause time4.3Running the TestThe performance of a protection relay at bus A can be tested by injecting the simulated voltages and the simulated currents and reading back the trip signal with a CMC test set.To run a single test click Single Test on the Home tab.4.4Results and Time SignalsThe Time Signal View shows that the resulting simulation resembles a practical "fault-reclosure-persisting-fault" sequence. Detailed investigations of the actual values of the voltages and the currents or timing can be made by using the cursors.The trip time and the pause time are automatically measured by the measurement conditions.Figure 4-5:Time assessment conditions with result and assessmentThe described test shows that NetSim provides flexible settings that allow a simple simulation of realistic events.27Multiple Faults on Parallel Lines5Multiple Faults on Parallel LinesTaskTo simulate a double line power transmission system under multiple fault occurrences. There are two faults involved; both of them are on different lines, at different times, and have different fault types. The two faults are: On Line 1: a line-line fault (A-B) at 20% of the line length On Line 2: a three-phase fault at 40% of the line length, 80ms after the fault on line 1The CBs switch off according to the tripping of the relays. Relays A, C, and D trip instantaneously, relay B has a slightly delayed transfer trip.The mutual coupling between the parallel systems has to be taken in account.SolutionThe simulation is performed with a network configuration as shown in the following figure:Figure 5-1:Network configuration for short circuit event simulation on double lineAgain, many of the settings are left as the default values, and they are not repeated throughout the manual. Only the essential settings are mentioned.Source 1Line 220 %Source 2Line 140 %28NetSim 5.1Selecting the Network ConfigurationClick Select Test Case on the Home tab to see the various network configurations. Select Parallel Line to get a network configuration as shown in figure 5-1 on page 27.Figure 5-2:Selecting a short circuit simulation on a parallel line5.2Entering the Source ParametersThe only parameter that needs to be modified on the Source tab is the angle of Source 2. It is set this way in order to obtain a sensible prefault current.A look at figure 5-1 on page 27 (and at the Lines tab) shows that the line segments between the generators and the busbars are not explicitly modeled in this configuration, so the total positive sequence impedance between the two generators is.Half of the current through this total impedance flows through each of the two parallel lines.Source LineZ Z, 1 , 12 2 +29Multiple Faults on Parallel LinesChoosing VSource2= 100 V