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ETAP PowerStation 4.0

User Guide

Copyright 2001 Operation Technology, Inc.

All Rights Reserved This manual has copyrights by Operation Technology, Inc. All rights reserved. Under the copyright laws, this manual may not be copied, in whole or in part, without the written consent of Operation Technology, Inc. The Licensee may copy portions of this documentation only for the exclusive use of Licensee. Any reproduction shall include the copyright notice. This exception does not allow copies to be made for other persons or entities, whether or not sold. Under this law, copying includes translating into another language. Certain names and/or logos used in this document may constitute trademarks, service marks, or trade names of Operation Technology, Inc. or other entities. • Access, Excel, ODBC, SQL Server, Windows NT, Windows 2000, Windows Me, Windows

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Chapter 17

Transient Stability Analysis

The PowerStation Transient Stability Analysis program is designed to investigate the stability limits of a power system before, during, and after system changes or disturbances. The program models dynamic characteristics of a power system, implements the user-defined events and actions, solves the system network equation and machine differential equations interactively to find out system and machine responses in time domain. From these responses, users can determine the system transient behavior, make stability assessment, find protective device settings, and apply the necessary remedy or enhancement to improve the system stability. This chapter describes different tools to assist you in running transient stability studies. An overview on the basics of transient stability study is also provided. This chapter is organized into 8 sections. The Transient Stability Toolbar section explains how you can launch a transient stability calculation, open and view an output report, select display options, and view plots. The Study Case Editor section explains how to create a new study case, to define parameters for a study case, to create a sequence of switching events and disturbances, to globally define machine dynamical modeling method, to select plot/tabulation devices, etc. The Display Options section explains what options are available for displaying some key system parameters and the output results on the one-line diagram, and how to set them. The Calculation Methods section provides some theoretical backgrounds and quick reference for the fundamentals on transient stability study, which are very helpful for users who do not have extensive experience on running transient stability studies. The Required Data section is a very good reference for you to check if you have prepared all necessary data for transient stability calculations. These data range from the system side, such as bus and branch information, to the machine side, such as machine model and parameters, exciter model and parameters, and governor model and parameters. The Output Reports section explains and demonstrates the format and organization of the transient stability text reports. The One-Line Diagram Displayed Results section explains the available one-line displaying results and provides one example. The Plots section explains what plots for transient stability are available and how to select and view them.

Operation Technology, Inc. 17-1 ETAP PowerStation 4.0

Transient Stability Analysis Toolbar

17.1 Transient Stability Toolbar The Transient Stability Toolbar will appear on the screen when you are in the Transient Stability Study mode.

Run Transient Stability Display Options Report Manager Transient Stability Plots Halt Current Calculation Get On-Line Data Get Archived Data

Run Transient Stability Select a study case from the Study Case Toolbar. Then click on the Run Transient Stability button to perform a transient stability study. A dialog box will appear to ask you to specify the output report name if the output file name is set to Prompt. When the calculation completes, the transient stability study results will appear on the one-line diagram and are stored in the output report, as well as in the plot file.

Display Options Click the Display Options button to customize the one-line diagram annotation options under the transient stability study mode. Also to edit the one-line diagram display for transient stability calculation results. See Display Options for more information.

Report Manager Click on Report Manager button to select a format and view transient stability output report. Transient stability analysis reports are current provided in ASCII formats only, which can be accessed from the Report Manager.



You can also select output files from the Output Report list box. This list contains all the output files in the current project folder with the same file extension specified. To change output file extensions, you can click on the List Output Reports button next to the Output Report list box, which will allow you to select a different output file extension.

The output reports for transient stability studies have a .tsr extension. PowerStation text output reports can be viewed by any word processor such as Notepad, WordPad, and Microsoft Word. Currently, by default, the output reports are viewed by Notepad. You can change the default viewer in the ETAPS.INI file to the viewer of your preference. Refer to Chapter 1, Product Description, or Chapter 7, Printing & Plotting for more details.



The output reports are 132 characters wide with 66 lines per page. For the correct formatting and pagination of output reports, you MUST modify the default settings of your word processor application. For Notepad, WordPad, and Microsoft Word applications we have recommend settings that are explained in Chapter 7, Printing & Plotting.

Transient Stability Plots Click on the Transient Stability Plots button to select and plot the curves of the last plot file. The plot file name is displayed on the Study Case Toolbar. The transient stability plot files have the following extension: .tsp. For more information see Plots section.

Halt Current Calculation The Stop Sign button is normally disabled. When a transient stability calculation has been initiated, this button becomes enabled and shows a red stop sign. Clicking on this button will terminate the current calculation. One-line diagram display will not be available if you terminate the calculation before it completes; but the text output report and plots do store the calculation results up to the time instant when you terminate the calculation.

Get On-Line Data If the ETAP key installed on your computer has the on-line feature, you can copy the on-line data from the on-line presentation to the current presentation.

Get Archived Data If the ETAP key installed on your computer has the on-line feature, you can copy the archived data to the current presentation.


Transient Stability Analysis Study Case Editor

17.2 Study Case Editor The Transient Stability Study Case Editor contains solution control variables, loading conditions, event and action specifications, machine modeling selections and a variety of options for output reports and plots. PowerStation allows you to create and save an unlimited number of study cases. Transient stability calculations are conducted and reported in accordance to the settings of the study case selected in the Study Case Toolbar. You can easily switch between study cases without the trouble of resetting the study case options each time. This feature is designed to organize your study efforts and save you time. As a part of the multi-dimensional database concept of PowerStation, study cases can be used for any combination of the three major system toolbar components, i.e. for any configuration status, one-line diagram presentation, and Base/Revision Data. When you are in the Transient Stability Analysis mode, you can access the Transient Stability Study Case Editor by clicking on the Study Case button on the Transient Stability Toolbar. You can also access this editor from the Project View by clicking on the Transient Stability subfolder under the Study Cases folder.

To create a new study case, go to the Project View, right-click on the Transient Stability Study Case folder, and select Create New. The program will then create a new study case, which is a copy of the default study case, and adds it to the Transient Stability Study Case folder.

The Transient Stability Study Case Editor consists of four pages: Info Page, Events Page, Dyn Model Page, and Plot Page.



17.2.1 Info Page This page is provided for you to specify some general solution parameters and study case information.

Study Case ID Study case ID is shown in this entry field. You can rename a study case by simply deleting the old ID and entering a new ID. Study case ID can be up to 12 alphanumeric characters. Use the Navigator button at the bottom of the editor to go from one study case to another.

Initial Load Flow In this section you can specify the solution parameters for initial load flow calculation in transient stability analysis.

Max Iteration Enter the maximum number of iterations. If the solution has not converged at the specified number of iterations, the program will stop and inform the user. The recommended and default value is 2000.

Solution Precision Enter the value for the solution precision that is used to check for convergence. This value determines how precise you want the final solution to be. The default (and recommended) value is 0.000001.

Accel. Factor Enter the convergence acceleration factor to be used between iterations. Typical values are between 1.2 and 1.7. The default value is 1.45.



Solution Parameters

Simulation Time Step This is the integration time step in seconds in transient stability simulation. You should set this number smaller than the smallest time constant in the system so you can see all the exciter and governor responses. Note that the smaller this number is, the more calculations are required, so the calculation time increases. The recommended value is 0.001 seconds. If you feel you need higher resolution, decrease this number. However, if the integration time step is too small, accumulated round up errors may increase.

Plot Time Step This value determines how often PowerStation should record the results of the simulation for plotting. For instance, if you specify 20 steps, PowerStation will plot points at every 20 simulation time step, i.e., for a simulation time step of 0.001, the plot time step will be .02 seconds. The smaller this number is, the smoother your plots will look, but also remember that the plot files on your hard disk may grow quite large. Keep in mind that PowerStation records plot information at this interval throughout the simulation. For example, if you specified a simulation time step of 0.001 seconds, plot time step of 10, and a total time of 20 seconds, PowerStation will write 20 / (0.001*10)= 2000 points to disk, which may be a very large plot file, depending on the number of machines and buses being plotted.

Apply XFMR Phase-Shift Select this option to include transformer phase-shift specified in the transformer editors in both transient stability initial load flow calculation and time simulation calculation. Otherwise transformer phase-shift will be ignored (i.e., 0 degree phase-shift regardless of the transformer winding connections).

Initial Loading In the Initial Loading block of the Transient Stability Study Case Editor, you can specify the system initial operating loads by selecting a loading. The initial loading conditions will establish an initial normal operation condition for the transient stability studies.

Loading Category Select one of the ten loading categories for this study case. With the selection of any category, PowerStation uses the percent loading of individual motors and other loads as specified for the selected category. Note that you can assign loading to each one of the ten categories in the Nameplate page, Loading page, or Rating page for most load components. Harmonic Filter loading is calculated from its parameters.

Operating Load Check this option to operate P and Q as specified in the relevant component editors.

Charger Loading

Load Category Select this option to use the P and Q specified in the Loading Category section of the Charger Editor for chargers.



Operating Load Select this option to use the P and Q as specified in the Operating Load section of the Charger Editor. If this option is selected, a DC load flow calculation is required to run first in order to estimate the charger load.

Load Diversity Factor Apply appropriate load diversity factor(s) for transient stability initial load flow calculation. The choices are:

None Select None to use the percent loading of each load as entered for the selected Loading Category, i.e., no diversity factor is considered.

Bus Maximum When the Bus Maximum option is selected, the loading of all motors and other loads will be multiplied by the maximum diversity factor of the bus, which they are directly connected to. Using this option, you can define the initial loading for transient stability studies with each bus having a different maximum diversity factor. This study option is helpful when the future loading of the electrical system has to be considered and each bus may have a different maximum diversity factor.

Bus Minimum When the Bus Minimum option is selected, the loading of all motors and other loads will be multiplied by the bus minimum diversity factor of the bus that they are directly connected to. Using this option, you can define the initial loading for transient stability studies with each bus having a different minimum diversity factor. This study option may be used to see the effect of transformer taps and capacitors (if any) on the system voltages under a minimum (light) loading condition.

Global When this option is selected, PowerStation will ask you to enter global diversity factors for constant kVA and constant Z loads, respectively. When you select this option, PowerStation will globally multiply all constant kVA and constant Z loads of the selected loading category with the entered values. When using this option, you can define the initial loading for transient stability analysis studies with fixed diversity factors for all loads. Note that a constant kVA load diversity factor of 125% implies that the constant kVA loads of all buses are increased 25% above their values as specified by the selected loading category. This value can be smaller or greater than 100%.

Remarks 2nd Line You can enter up to 120 alphanumeric characters in the Remarks box. Information entered in this location will be printed on the second line of the header information in every page of the output report. These remarks can provide specific information and conditions for each study case. Note that the first line of the header information is global for all study cases and is entered in the Project Information Editor.



17.2.2 Events Page This page is provided for you to design and store transient stability study scenarios and events.

Events In this list, all events are displayed in their time order to give you a clear picture of the event sequence in this study. The active events are marked by '*' and are listed first, followed by those which are inactive.

Event ID The Event ID is a unique name with a maximum length of 12 alphanumeric characters.

Time This is the time when the associated event occurs. The unit is in second.

Add (Event) A new event can be added by clicking on the Add (Event) button and opening the Event Editor.

Active Select this option to make an event active. Clicking on the box again will make the event inactive. Only active events will be included in the study.



Edit (Event) Click on the Edit (Event) button to open the Event Editor and edit an existing event. You can also double-click on an event in the Event list to activate the Event Editor.

Delete (Event) Delete an existing event from the list.

Actions Each event can encapsulate a number of actions (system changes or disturbances). When you select an event by highlighting that event in the Event list, the actions associated with that event will be displayed in the Action list. Each action is composed of the information of the Device Type, the Device ID, and an Action. Note that the event ID is displayed on top of the Action list for your reference.

Device Type The type of device that is going to take an action.

Device ID The ID of the device that is going to take an action.

Action The action to be taken by the specified device and the device type. The following is a table showing device types and their associated actions:

Device Type Actions Bus Fault / Clear Fault Cable Fault at ¼ /Fault at ½ / Fault at ¾ / Clear Fault Line Fault at ¼ /Fault at ½ / Fault at ¾ / Clear Fault Impedance Fault at ¼ /Fault at ½ / Fault at ¾ / Clear Fault Circuit Breaker Open / Close SPST Switch Open / Close Fuse Open / Close Generator Ref. Machine / Delete / Droop / Isoch / Start / Loss Excitation Utility Ref. Machine / Delete Syn. Motor Delete Ind. Motor Accelerate / Delete MOV Start None Load Flow (no action, print load flow at the event time)

Add (Action) A new action can be added by clicking on the Add (Action) button and opening the Action Editor. Select a device type from the Device Type drop-down list. Select the device ID from the Device ID drop-down list. Select an action from the Action drop-down list.

Edit (Action) Click on the Edit (Action) button to edit an existing action. You can also double-click on a listed action to bring up the Action Editor.



Delete (Action) Delete an existing action.

Total Simulation Time The total simulation time for a transient stability study. The unit is in seconds.

17.2.3 Dyn Model Page This page is provided to globally specify if you want to dynamically model synchronous and induction motors in the system. Motors are subdivided into medium voltage (above 1.0 kV) and low voltage (less than or equal to 1.0kV) synchronous motor and induction machine groups.

A machine will be dynamically modeled if you have specified a dynamic model in its editor and you select to globally model that motor group from this page. Note that all synchronous generators are dynamically modeled.

Machine Type

Syn. Motors, MV The machine group consisting of all synchronous motors, which are medium voltage (rated above 1.0 kV).



Syn. Motors, LV The machine group consisting of all synchronous motors that are low voltage (rated less than or equal to 1.0 kV).

Ind. Machines, MV The machine group consisting of all induction machines that are medium voltage (above 1.0 kV).

Ind. Machines, LV The machine group consisting of all induction machines that are low voltage (rated less than or equal to 1.0 kV).

Dynamic Modeling

Do Not Model If selected, the corresponding machine group will not be dynamically modeled in the transient stability study for this study case, regardless of dynamic models specified for individual machines.

Model Machines Larger or Equal To If selected, machines that are in the corresponding machine group and rated larger than the size specified in the HP/kW field will be dynamically modeled, and machines in the same group that are rated less than the size specified will not be dynamically modeled. Note that for the machine to be dynamically modeled, it should also have a dynamic model specified for it from its editor.

HP/kW Specify the size of machines (in HP or kW) for the selected machine group to be dynamically modeled.

Starting Load for Accelerating Motors Specify the base for load torque vs. slip models used for accelerating motors.

Based on Motor Electrical Rating Load torque vs. slip curve is defined based on the motor electrical rating, i.e., the load torque vs. slip curve will be scaled to reach 100% at the synchronous speed, corresponding to 100% of the motor electrical rating.

Based on Motor Mechanical Load Load torque vs. slip curve is defined based on the motor mechanical load, i.e., the load torque vs. slip curve will not be scaled.

Generator Start-Up Specify special frequency dependent models for generator start-up studies here.

Frequency Dependent Models for Network, Motors, & Generators The network, motors, and generators will be modeled as frequency dependent. This option has to be checked in order to perform the generator start-up study.



17.2.4 Plot Page This page is provided for you to select devices to be plotted for viewing transient stability study results.

Device Type Select a device type.

Syn. Generators The machine group consisting of all synchronous generators.

Syn. Motors, MV The machine group consisting of all dynamically modeled synchronous motors, which are rated above 1.0 kV.

Syn. Motors, LV The machine group consisting of all dynamically modeled synchronous motors which are rated equal to or less than 1.0 kV.

Ind. Machines, MV The machine group consisting of all dynamically modeled induction machines, which are rated above 1.0 kV.



Ind. Machines, LV The machine group consisting of all dynamically modeled induction machines which are rated equal to or less than 1.0 kV. Buses The device group consisting of all buses.

MOVs The device group consisting of all MOVs with initially open or closed status.

Branches The device group, consisting of all different types of branches, with the exception of tie circuit breakers (protective devices).

Plot Options Once a machine or device group is selected, all devices in that group will be displayed in the Plot Options list for you to select.

Device ID Device IDs for the selected machine or device group, excluding the non-dynamically modeled machines.

Plot/Tabulation (column) You can click on this column to select or deselect the plot/tabulation option for a particular device. Once this option is set, an X will show in this column next to the selected device. By selecting this option, information for the selected device will be tabulated at the end of the transient stability output report and stored in the plot file to be plotted.

Plot/Tabulation (check box) This provides another way to set the plot/tabulation option for the highlight device.


Transient Stability Analysis Display Options

17.3 Display Options The Transient Stability Analysis Display Options consist of a Results page and three pages for AC, AC-DC, and DC info annotations. Note that the colors and displayed annotations selected for each study are specific to that study.

17.3.1 Results Page The Results page allows you to define options for one-line diagram calculation results display. These results can be displayed for each plot time step as selected from the Time Slider. The results include bus voltage and frequency, synchronous machine power angle and frequency, induction motor speed, and power flow to machines. The bus and machine data that are displayed on the one-line diagram are the same data, which are stored in the plot file, i.e., to show a bus voltage and frequency on the one-line diagram, you need to request a plot for that bus.

Color Select the color for result annotations to be displayed on the one-line diagram.

Show Units Select the check boxes under this heading to show units for the displayed results.

Bus Display the calculated voltage and frequency of buses selected for plotting.

Voltage Bus voltage in kV or in percent of the bus nominal kV.

Frequency Bus frequency in hertz or in percent of system frequency.



Syn. Machines Display the calculated power angle and frequency of synchronous generators and motors, which are selected for plotting from the Study Case.

Power Angle Machine power (rotor) angle in degrees or radians.

Frequency Machine frequency in hertz or in percent of system frequency.

Ind. Machines

Speed Display speed of induction machines (RPM or % Slip), which are selected for plotting from the Study Case. % Slip = (ωs - ωm ) / ωs

Machine Flows Specify how the flows will be displayed in (kW+jkvar or MW+jMvar), or (kVA or MVA), or Amp.

Transient Stability Study Results Displayed on the One-Line Diagram at Time 1.38 Seconds



17.3.2 AC Page This page includes options for displaying info annotations for AC elements.

Color Select the color for information annotations to be displayed on the one-line diagram.

ID Select the check boxes under this heading to display the ID of the AC elements on the one-line diagram.

Rating Select the check boxes under this heading to display the ratings of the AC elements on the one-line diagram.

Device Type Rating Gen. (Generator) kW / MW Power Grid (Utility) MVAsc Motor HP / kW Load kVA / MVA Panel Connection Type (# of Phases - # of Wires) Transformer kVA / MVA Branch, Impedance Base MVA Branch, Reactor Continuous Amps Cable / Line # of Cables - # of Conductor / Cable - Size Bus kA Bracing Node Bus Bracing (kA) CB Rated Interrupting (kA) Fuse Interrupting (ka) Relay 50/51 for Overcurrent Relays PT & CT Transformer Rated Turn Ratio

kV Select the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram. For cables/lines, the kV check box is replaced by the button. Click on this button to display the cable/line conductor type on the one-line diagram.

A Select the check boxes under this heading to display the ampere ratings (continuous or full-load ampere) of the selected elements on the one-line diagram. For cables/lines, the Amp check box is replaced by the button. Click on this button to display the cable/line length on the one-line diagram.



Z Select the check boxes under this heading to display the rated impedance of the selected AC elements on the one-line diagram.

Device Type Impedance Generator Subtransient reactance Xd” Power Grid (Utility) Positive Sequence Impedance in % of 100 MVA (R + j X) Motor % LRC Transformer Positive Sequence Impedance (R + j X per unit length) Branch, Impedance Impedance in ohms or % Branch, Reactor Impedance in ohms Cable / Line Positive Sequence Impedance (R + j X in ohms or per unit length)

D-Y Select the check boxes under this heading to display the connection types of the selected elements on the one-line diagram. For transformers, the operating tap setting for primary, secondary, and tertiary windings are also displayed. The operating tap setting consists of the fixed taps plus the tap position of the LTC.

Composite Motor Click on this check box to display the AC composite motor IDs on the one-line diagram, then select the color in which the IDs will be displayed.

Use Default Options Click on this check box to use PowerStation’s default display options.

17.3.3 AC-DC Page This page includes options for displaying info annotations for AC-DC elements and composite networks.


ID Select the check boxes under this heading to display the IDs of the selected AC-DC elements on the one-line diagram.

Rating Select the check boxes under this heading to display the ratings of the selected AC-DC elements on the one-line diagram.

Device Type Rating Charger AC kVA & DC kW (or MVA / MW) Inverter DC kW & AC kVA (or MW / MVA) UPS kVA VFD HP / kW



kV Click on the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram.

A Click on the check boxes under this heading to display the ampere ratings of the selected elements on the one-line diagram.

Device Type Amp Charger AC FLA & DC FLA Inverter DC FLA & AC FLA UPS Input, output, & DC FLA

Composite Network Click on this check box to display the composite network IDs on the one-line diagram, then select the color in which the IDs will be displayed.

Use Default Options Click on this check box to use PowerStation’s default display options.

17.3.4 DC Page This page includes options for displaying info annotations for DC elements.


ID Select the check boxes to display the IDs of the selected DC elements on the one-line diagram.

Rating Select the check boxes to display the ratings of the selected DC elements on the one-line diagram.

Device Type Rating Battery Ampere Hour Motor HP / kW Load kW / MW Elementary Diagram kW / MW Converter kW / MW Cable # of Cables - # of Conductor / Cable - Size

kV Select the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram. For cables, the kV check box is replaced by the button. Click on this button to display the conductor type on the one-line diagram.



A Select the check boxes under this heading to display the ampere ratings of the selected elements on the one-line diagram. For cables, the Amp check box is replaced by the button. Click on this button to display the cable length (one way) on the one-line diagram.

Z Select the check boxes under this heading to display the impedance values of the cables and impedance branches on the one-line diagram.

Composite Motor Click on this check box to display the DC composite motor IDs on the one-line diagram, then select the color in which the IDs will be displayed.


Transient Stability Analysis Calculation Methods

17.4 Calculation Methods Performing the power system transient stability study is a very comprehensive task. It requires knowledge of machine dynamic models, machine control unit models (such as excitation system and automatic voltage regulators, governor and turbine/engine systems, and power system stabilizers), numerical computations, and power system electromechanical equilibrium phenomena. The full discussion on this topic is far beyond the scope of this manual. In this section, we will brief you with some fundamentals and underlying principles on the power system transient stability study, with the focus on applications with PowerStation.

Purpose for Performing Transient Stability Study Dynamic performance of a power system is significant in the design and operation of the system. The transient stability study determines the machine power angles and speed deviations, system electrical frequency, real and reactive power flows of the machines, power flows of lines and transformers, as well as the voltage levels of the buses in the system. These system conditions provide indications for system stability assessments. The results are displayed on the one-line diagram, and also can be printed or plotted. For transient stability studies, you should model particular groups of machines in the system that are known to have important influences on the system operation. The total simulation time for each study case should be sufficiently long to obtain a definite stability conclusion.

Power System Stability Definition Power system stability is the property of a power system that insures the system remains in electromechanical equilibrium throughout any normal and abnormal operating conditions. Because the power system stability is an electromechanical phenomenon, it is thus defined as the ability of designated synchronous machines in the system to remain in synchronism with one another following disturbances such as fault and fault removal at various locations in the system. It also indicates the ability of induction motors in the system to maintain torque to carry load following these disturbances.

Synchronous Machine Rotor Angles Synchronous machines play a decisive role in the power system stability because during and after disturbances their rotor angles will oscillate to cause power flow oscillations in the system. Depending on the level of these oscillations, the electromechanical equilibrium in the system could be destroyed and the instability could occur. Therefore, power system stability is sometimes also referred to as synchronous machine rotor angle stability. The following two equations are often referenced in power system transient stability studies: Torque Equation (Generator Case)

δφπsin

8

2

rFairP

T =

where T = mechanical shaft torque P = number of poles φair = air-gap flux Fr = rotor field MMF δ = power (rotor) angle



The torque equation defines the relationship between the mechanical shaft torque, the stator voltage, the excitation system, and the rotor angle. Changes in any one of them will cause the rotor angle to readjust itself to a new position. Swing Equation (Generator Case)

elecPmechPdtd

Ddt

dM −=+

δδ2

2

where M = inertia constant D = damping constant Pmech = input mechanical power Pelec = output electrical power The swing equation shows that the solution of the rotor angle is a function of balance between the mechanical power and the electrical power. Any change in the system that breaks this balance will cause the rotor angle to undergo a transient and reach a new position in an oscillatory manner. This oscillation is usually called the rotor angle swing.

Stability Limits There are two types of stability limit for a power system, namely steady-state stability limit and transient stability limit.

Steady-State Stability Limit The steady-state stability is defined as the stability of a system under conditions of gradual or small changes in the system. This stability can be either found by the load flow calculation for a steady-state operation, or determined by a transient stability study if there are system changes or disturbances involved. The system is said to be steady-state stable if, following any small and/or gradual disturbances, all synchronous machines reach their steady-state operating condition identical or close to the pre-disturbance operating conditions. The steady-state stability limit for any synchronous machine is when its rotor angle is less than 90 degrees.

Transient Stability Limit Transient or dynamic stability is defined as the stability of a system during and after sudden changes or disturbances in the system, such as short-circuits, loss of generators, sudden changes in load, line tripping, or any other similar impact. The system is said to be transient stable if following a severe disturbance, all synchronous machines reach their steady-state operating condition without prolonged loss of synchronism or going out of step with other machines.

Causes of Instability Problems The major causes to industrial power system instability problems include, but are not limited to: • Short-circuits • Loss of a tie connection to a utility system • Loss of a portion of in-plant co-generation (generator rejection) • Starting a motor that is large relative to the system generating capacity • Switching operations of lines, capacitors, etc. • Impact loading (motors and static loads) • A sudden large step change of load or generation



Consequences of Instability Problems The consequences of power system instability problems usually are very severe and can range from permanent damage on equipment and shutting down processes, all the way to causing a whole area power outage. Some typical consequences are listed below: • Area-wide blackout • Interruption of loads • Low-voltage conditions • Damage to equipment • Relay and protective device malfunctions

Power System Transient Stability Enhancement Depending on the causes of instability problems in a particular system, a number of enhancements can be made to improve the system stability. Typical enhancements include: • Improve configuration and system design. • Increase synchronizing power • Design and selection of rotating equipment – use induction motors, increase moment of inertia,

reduce transient reactance, improve voltage regulator and exciter characteristics • Application of Power System Stabilizers (PSS) • Add system protection – fast fault clearance, system separation, etc. • Add load shedding scheme However, note that each of the above remedies requires careful consideration and we recommend that you re-run all system studies again, because changes brought by those remedies very likely will impact system load flow, short-circuit, and motor starting results.



Simulation of Time Events and Actions Transient Stability study is essentially an action driven time-domain simulation. Actions should be specified at different time instants (events). There are two ways to specify events and actions. One way is to use the Event Editor and Action Editor in the Transient Stability Study Case Editor. Another way is to use relay-controlled dynamic actions. When using actions specified in the Transient Stability Study Case Editor, Action List, the exact time instant for the action to take place needs to be given. Type of actions in this category includes all the pre-scheduled operations such as generator start-up and shutdown, generator control mode change, load addition and rejection, motor acceleration, MOV start and others. When to simulate the system response for existing events, such as a recorded fault in the system, user also can use this type of action, because the recorded fault occurring time and duration are known. To specify this type of actions, user first creates a new event and the event occurring time in the Event Editor of the Transient Stability Study Case Editor, Event page, as shown below.

Secondly, user can use the Action Editor in the same page to add as many actions as desired for this event.



A complete list of devices in ETAP PowerStation that can be specified with actions and types of these actions is given in section 2.2 Events Page, of this chapter, under subsection Actions. However, in power systems, many actions occur without any pre-acknowledgment, instead, they are controlled by sensors and relays. For instance, a current relay will trip off circuit breakers once the measured current by relay exceeds a pre-set value. In another case, a voltage relay can be used to open or close circuit breakers based on its monitored voltage and comparison with an upper and an lower settings. These types of action do not have a definite time of happening and are solely depending on the system dynamic responses and relay settings. They, therefore, have to be implemented using the second method, i.e., relay controlled actions. To use relay-controlled actions, user need to add a relay and connect it to the one-line diagram via a PT or CT, depending on type of the relay. Next in relay editor, user specifies relay-controlled circuit breaker ID, control settings, time delay, and other data related to relay operations. During the transient stability simulation in time-domain, if a relay setting is met, then its controlled circuit breaker will take an automatic action. This method avoids requesting to give a pre-defined action time and is a true resemblance to power system real operating conditions. Following two pictures give an example of how to use relay-controlled actions. In the first picture, assuming CB2 and/or CB11 are tripped off due to a fault in transformer T2, thus substation Sub2A-N losses power. To make a bus transfer for Sub2A-N to the adjacent bus Sub2B, user can place a voltage relay (27) on bus Sub2A-N to monitor the bus voltage magnitude and close a normally opened tie circuit breaker Tie CB when it is necessary.



To do so, user can set the voltage relay to pick up under-voltage at 65% and close Tie CB after 0.1 relay delaying time and what ever the closing cycle by Tie CB itself. Settings for the voltage relay is shown in the second figure down below.


Transient Stability Analysis Required Data

17.5 Required Data To run a transient stability study, you need to provide all the data required for load flow calculation. In addition to that, you need to provide machine dynamic model data, load model data, and any control units, such as exciter and governor data. Required data for transient stability calculations include:

Bus Data • Bus ID • Nominal kV • Load Diversity Factor (when Loading option is set to Maximum or Minimum diversity factor)

Branch Data

2-Winding and 3-Winding Transformers • Transform ID • Bus Connections • Rated kV and MVA • Impedance and tolerance • X/R ratio • Tap and LTC settings • Phase Shift as in Standard Positive or Negative Sequence connections, or Special configurations

Cable/Transmission Line • Cable or Transmission Line ID • Bus Connections • Type, size, rated kV, # of conductors per phase, and length • Use library data or enter cable's resistance, reactance, and susceptance values

Impedance • Impedance ID • Bus Connections • Resistance, reactance, and susceptance values

Current-Limiting Reactor • Current-Limiting Reactor ID • Bus Connections • X/R ratio, impedance, and tolerance

Protective Device Data • Protective Device ID • Bus and Branch Connections • Status

CT/PT Data • CT/PT ID • Bus or Branch or Source or Load Connections • Rating (Ratio)



Relay Data • Relay ID • CT/PT Connections • Device, CB ID, Action, Delay, Setting, Unit

Power Grid Data • Power Grid ID • Bus Connections • Operating mode (Swing, Voltage Control, or Mvar Control) • Nominal kV • %V and Angle for Swing mode • %V, MW loading, and Mvar limits (Qmax & Qmin) for Voltage Control mode • MW and Mvar loading for Mvar Control mode • 3-Phase MVAsc and X/R values

Synchronous Generator Data • Synchronous generator ID • Bus Connections • Operating mode (Swing, Voltage Control or Mvar Control) • Rated kV • %V and Vangle for Swing mode of operation • %V, MW loading, and Mvar limits (Qmax & Qmin) for Voltage Control mode of operation • MW and Mvar loading for Mvar Control mode of operation • Rated MVA • Model type (None, Equivalent, Transient, or Subtransient) • Machine type (Round-Rotor or Salient-Pole) • Xd”, Xd’, Xd, Xq, Xl, X/R, Tdo’ for Equivalent model • Xd”, Xd’, Xd, Xq’, Xq, Xl, X/R, Tdo’, Tqo’ for Transient model Round-Rotor machine type • Xd”, Xd’, Xd, Xq”, Xq’, Xq, Xl, X/R, Tdo”, Tdo’, Tqo”, Tqo’ for Subtransient model Round-Rotor

machine type • Xd”, Xd’, Xd, Xq’ (= Xq), Xq, Xl, X/R, Tdo’ for Transient model Salient-Pole machine type • Xd”, Xd’, Xd, Xq”, Xq’ (= Xq), Xq, Xl, X/R, Tdo”, Tdo’, Tqo” for Subtransient model Salient-Pole

machine type • S100, S120, H, and Damping • Sbreak for Generator Start-up Study • Exciter Type and all associated parameters or fixed excitation • Governor Type and all associated parameters or no governor action • Power System Stabilizer (PSS) Type and all associated parameters or no PSS control



Synchronous Motor Data • Synchronous motor ID • Bus Connections • Quantity • Rated kW/hp and kV • Power factors and efficiencies at 100%, 75%, and 50% loadings • Loading Category ID and % Loading • Equipment cable data • Model type (None, Equivalent, Transient or Subtransient) • Machine type (Round-Rotor or Salient-Pole) • Xd”, Xd’, Xd, Xq, Xl, X/R, Tdo’ for Equivalent model • Xd”, Xd’, Xd, Xq’, Xq, Xl, X/R, Tdo’ for Transient model Round-Rotor machine type • Xd”, Xd’, Xd, Xq”, Xq’, Xq, Xl, X/R, Tdo”, Tdo’, Tqo”, Tqo’ for Subtransient model Round-Rotor

machine type • Xd”, Xd’, Xd, Xq’ (= Xq), Xq, Xl, X/R, Tdo’ for Transient model Salient-Pole machine type • Xd”, Xd’, Xd, Xq”, Xq’ (= Xq), Xq, Xl, X/R, Tdo”, Tdo’, Tqo for Subtransient model Salient-Pole

machine type • S100, S120, H and Damping • Exciter Type and all associated parameters or fixed excitation • H • Load model Induction Machine Data • Induction machine ID • Bus Connections • Application type (motor or generator) • Quantity • Rated kW/hp and kV • Power factors and efficiencies at 100%, 75%, and 50% loadings • Loading Category ID and % Loading • Equipment cable data • Model type (None, Single1, Single2, DBL1, or DBL2) • Xlr, Xoc, X/R, and Tdo’ for Single1 model • Rs, Xs, Xm, Rr,fl, Rr,lr, Xr,fl, and Xr,lr for Single2 model • Rs, Xs, Xm, Rrl, Rr2, Xr1, and Xr2 for DBL1 and DBL2 model • H • Load model • % Start Loading for the First Starting Category (defines the motor start loading percent)



MOV Data • MOV ID • Bus Connection • Quantity • Initial Status & Associated Demand Factor • Rated kW/hp & kV • Power Factor & Efficiency • Rated Torque • Hammer Blow & Micro Switch Flags • Locked Rotor (LR), No Load (NL), Normal, & Rated Torque (Rated T) Time Duration • Loading Category ID & % Loading • Equipment Cable Data • % Voltage Limit

Static Load Data • Static Load ID • Bus Connection • Quantity • Status & Associated Demand Factor • Rated kVA/MVA & kV • Power Factor • Loading Category ID & % Loading • Equipment Cable Data

Lumped Load Data • Lumped Load ID • Bus Connection • Status & Associated Demand Factor • Rated kVA/MVA & kV Power Factor • % Motor Load & % Static Load • Loading Category ID & % Loading

Capacitor Data • Capacitor ID • Bus Connection • Status & Associated Demand Factor • Rated kV • Mvar/Band and # of Bank • Loading Category ID & % Loading • Equipment Cable Data



Harmonic Filter • Harmonic Filter ID • Filter Type • Rated kV & 3-Phase kvar for Capacitors • Xl & Q for Reactors • R, if applicable • Grounding Connection • Grounding Type

UPS Data • UPS ID • Bus Connection • AC Connections • Rated kW/MW & kV • AC Input & Output Rated kV • Power Factor & Efficiency • Loading Category ID & % Loading

VFD Data • VFD ID • Bus Connection VFD is Modeled as a Transparent Device in the Transient Stability Study

Charger Data • Charger ID • Bus Connections • Status & Associated Demand Factor • AC Ratings • Loading Category ID & % Loading

Inverter Data Inverter is not Modeled in the Transient Stability Study



Study Case Parameters • Study Case ID • Max. Number of Iterations • Solution Precision • Acceleration Factor • Simulation Time Step • Plot Time Step • Initial Loading Category • Initial Loading Condition (Loading Category, Operating Load) • Load Diversity Factor (None, Bus Maximum, Bus Minimum, or Global) • Charger Loading Condition (loading Category, Operating Load) • Total Simulation Time • Events & Actions • Dynamic Modeling Information • Starting Load Modeling Method • Plots/Tabulated Selection Study Case parameters are entered into the Transient Stability Study Case Editor.


Transient Stability Analysis Output Reports

17.6 Output Reports PowerStation provides transient stability study results at all different levels of detail, depending on your requirements. The results are reported in three different formats: a text output report, a one-line view display, and plots.

17.6.1 Transient Stability Report Manager Click on the View Output File button on the Transient Stability Toolbar to open the Transient Stability Report Manager. The Transient Stability Report Manager provides the format for text and consists of four pages.

Complete Page From this page you can select the report format that gives you the complete output report. Currently, only the TextRept format is available.

Input Page This page provides the formats for different input data. Currently, the formats in this page are not available for the transient stability study.

Result Page This page provides the formats for different calculation results. Currently, the formats in this page are not available for the transient stability study.

Summary Page This page provides the formats for different summaries from both input data and calculation results. Currently, the formats in this page are not available for the transient stability study.



17.6.2 Transient Stability Text Report The text output report can be viewed by clicking on the View Output File button in the Study Case Toolbar or from the Transient Stability Report Manager by selecting TextRept and clicking on OK. The transient stability analysis output report consists of several sections, as summarized below.

Cover Page This is the first page of the output report. It includes information on the number of different types of buses, the number of different types of branches, the number of different types of machines; system parameters such as initial loading category, frequency, and unit system; solution parameters such as maximum iterations and solution precision; study parameters such as integration time step and plot time step, as well as output and plot file names.

DYNAMIC STABILITY ANALYSIS

--------------------------

Swing Gen. Load Total

----- ----- ----- -----

Number of Buses: 1 1 6 8

XFRM XFRM3 React. Line Imp. C.B. SPDT Total

----- ----- ----- ----- ----- ----- ----- -----

Number of Branches: 3 1 0 2 0 0 0 6

Synch. Synch. Ind. Uti-

Gen. Motor Motor lity Total

----- ----- ----- ----- -----

Number of Machines: 1 2 2 1 6

Initial Loading: Design

Maximum Number of Iterations: 2000

Solution Precision for the Initial LF: 0.00000100

Acceleration Factor for the Initial LF: 1.45

Time Increment for Integration Steps: 0.0010 Sec.

Time Increment for Plots: 0.0200 Sec.

System Frequency: 60.0 Hz

Unit System: English

Data Filename: EXAMPLE

Bus Input Data This section contains information for all the buses in the system, including bus ID, bus type (swing, generator, or load), nominal voltage, initial voltage magnitude and angle, MW and Mvar generation, Mvar limits, MW and Mvar motor load, MW and Mvar static load, etc. These data are the same as those in load flow output report and thus a sample printout is omitted.

Branch Input Data This section contains the information for all branches in the system, including branch ID, R, X, Y, X/R, transformer tap and LTC, and all the related information on branch impedance. Branch connections are also reported. These data are the same as those in load flow output report, thus a sample printout is omitted.



Power Grid, Synchronous Machine Data This section contains the information for all utility equivalent machines, synchronous generators, and the dynamically modeled synchronous motors in the system, including machine ID, connected bus ID, machine type and model type, rated kV and MVA, impedance data, time constants, inertia, damping, and saturation factors. For synchronous motors, it also contains the information on the load model and parameters.

Conned Bus Synch. GEN./MTR Rating (base) Machine Impedance ( % )

============ ====================== =============== ==============================================================

Bus ID Machine ID TYP MDL kV MVA Ra Xd" Xd' Xd Xq" Xq' Xq Xl

------------ ------------ --- --- ------ ------- ------ ------ ------ ------ ------ ------ ------ ------

Sub 2B Gen1 GEN 4 13.800 8.824 1.00 24.00 37.00 115.00 34.00 75.00 75.00 15.00

Main Bus Utility UTL 0 34.500 1500.000 2.22 99.98

Sub 2B Syn1 MTR 4 13.200 1.170 0.56 15.38 23.00 110.00 12.00 23.00 108.00 11.00

Bus3 Syn4 MTR 4 13.200 2.982 0.33 15.38 23.00 110.00 12.00 23.00 108.00 11.00

Synch. GEN./MTR Time Constant (sec) H(sec), D(MWpu/Hz) & Sat. Gen./Loading

====================== ============================== ========================== ==============

Machine ID TYP MDL Tdo" Tdo' Tqo" Tqo' H % D S100 S120 MW Mvar

------------ --- --- ------ ------ ------ ------ ----- ----- ----- ----- ------ ------

Gen1 GEN 4 0.030 5.000 0.050 3.700 1.200 5.00 1.070 1.180 6.300 0.000

Syn1 MTR 4 0.002 5.600 0.002 3.700 1.000 2.00 1.070 1.180 0.995 -0.617

Syn4 MTR 4 0.002 5.600 0.002 3.700 1.000 2.00 1.070 1.180 2.770 1.105

Synch. MTR Load Model

====================== ================================================

Machine ID TYP MDL Model ID A0 A1 A2 A3

------------ --- --- ------------ ------ ------ ------ ------

Syn1 MTR 4 COMP CENT 10.00 -91.00 321.00 -147.00

Syn4 MTR 4 Centr. Comp 10.00 -91.00 328.00 -147.00

Exciter/AVR Data This section contains the information for all exciters installed in the system, including the generator ID to which the exciter is installed, exciter type, gains, time constants, and other parameters.

Generator Type Time Constants (Sec.) and Parameters

============== ======== ==================================================================================================

1,2,3&1S KA KE KF TR TA TE TF/TF1 TF2/XL VRmax VRmin SEm/KP SE7/KI Efd/VB

DC1 &DC2 KA KE KF TA TB TC TE TF TR VRmax VRmin SEmax SE75 Efd

DC3 KE KV TE TR TRH VRmax VRmin SEmax SE75 Efd

ST1, ST2 KA KC KE/KG KF/KJ KI KP KPreal KPimg TA TB TC TE TF TR

& ST3 XL VGmax VImax VImin VRmax VRmin SEmax SE75 Efdmax

AC1 &AC4 KA KC KD KE KF TA TB TC TE TF TR

VAmax VAmin VImax VImin VRmax VRmin SEmax SE75 Efd

AC2 &AC3 KA KB/KR KC KD KE KF KH/KN KL(V) TA TB TC TE TF TR

VLR VLV Efdn VAmax VAmin VRmax VRmin SEmax SE75 Efd

SR8F KA KF TR TA TB TF1 TF2 VRmax VRmin

HPC 840 C D Kpow KQ KE Bmax Bmin Amax Amin VRmax VRmin SEmax SE75 Efd

Te T4 TI TD TF Tdsty TP TQ CtlBus

AC5A KA KE KF VRmax VRmin SEmax SE75 Efd

TA1 TA2 TA3 TE TF1 TF2 TF3 TR

JEUM Ar1 Ar2 Ku1 Ku2 Kif Kae Ke Vres Vsup SEm SE7 Efdmax Te

Max1 Min1 Max2 Min2 Max3 Min3 Max4 Min4 Max5 Min5 Max6 Min6 Max7 Min7

Av1 Av2 Av3 Av4 Av5 Av6 Av7 Av8 Av9 Av10 Av11

Ai1 Ai2 Ai3 Ai4 Ai5 Ai6 Ai7 Ai8 Ai9 Ai10 Ai11 Ai12

ST1D KA KC KF KVF KVL TA TB TC TD TH TF TR TVL

ID VImax VImin VRmax VRmin RC XC VVLR Vdc Rf VHZ Vfb Ifb Vref

-------------- -------- ------- ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------

Gen1 1 250.00 1.000 0.060 0.005 0.030 1.250 1.000 17.50 -15.50 1.650 1.130 6.600



Governor/Turbine Data This section contains the information for all governors installed in the system, including generator ID to which the governor is installed, governor type, mode, gains, time constants, and other parameters.

Type Operation Limits Time Constants(Sec.) and Parameters

====== ============= ============== ====================================================================

All ST %Droop Mode Pmax Pmin Tsr Tc Tch Trh1 Trh2 Tco Fhp Fvhp Fip

GT&GP %Droop Mode Pmax Pmin Tsr Tc Tt Tdrp Ta

DT,GTF %Droop Mode Pmax Pmin T1 T2 T3 T4 T5 T6 T7 T8 T9

&STM %Droop Mode Pmax Pmin K1/Kr K2/Kf K3/KD K4/Ff K5 K6 K7 DB UO/VU UC/VL

UG8 Mode Pmax Pmin A1 A2 A3 B1 B2 C1 K1 Ad T7 T8

Generator GTH& Ki Mode Max. Min. X Y Z A/a B/b C/c D Kf T.Ctl A.Ctl

GTS Tf/R Tcr/S Tcd/T Ttd T Tt Tr

505E Mode P1 I1 SDr1 L1 L2 Ta1 Tm1 Ts Prior Ramp

ID HPa HPb HPc HPmax Sa Sb Sc Smax EFmax

P2 I2 SDr2 L3 L4 Ta2 Tm2 EP EF

2301A %Droop Mode eMax eMin Alpha Beta Rho K1 Tao T1 T2 LS GP Pmax Pmin

MARS %Droop Mode T1 T2 T3 T5 T6 T7 Ks Kt Ko Ku

Kl MaxGv MinGv Maxo Mino Max2 Min2 Max3 Min3

DDEC %Droop Mode Pmax Pmin K1 K2 R1 Ts T1 T2 T3

GHH VLmax VLmin VMmax VMmin VHmax VHmin PLmax PLmin PMmax PMmin

PHmax PHmin Kp1 Kp2 Kp3 Kp4 GL GM GH m1

m2 m3 e1 e2 HP MP Pa Pb Pc Pd

Pe Pf LFa LFc LFd EX2f LFV1 LFV2 LFV3 LF1

LF2 LF3 FL0 KFL0 FL1 FM0 KFM0 FM1 Tn1 Tn2

Tn3 Tn5 Tn6 TL TM TH Esf1 Esf2

HYDR VO VC1 VC2 Gmax1 Gmax2 Gmin Q GC RP RT

TP TG TR Zt Zp1 ft fp1 Tt Tp1 At1

Damp QNL Q2 RPM1 RPM2 RPM3 GBUFF Wref Href m

B

SGT Mode Pmax Pmin T1 T2 T3 T4 T5 T6 TR K1 K2 K3

Pref

PL-A Fuel TP TL TQ TLD TLG TA TC TD TV TPL

TPG TC1 TC2 TX1 TX2 TX3 TX4 TX5 KL KI

KA KC KT DL JRL1 JRL2 TFLD Tref Plimit GOVBase

============ ------ ------ ----- ------ ------ ----- ----- ----- ----- ----- ----- ----- ----- ----- -----

Gen1 ST1 5.0 Droop 8.33 0.00 0.100 0.100 0.150 5.000 0.700

PSS Data This section contains the information for all PSS installed in the system, including generator ID to which the PSS is installed, PSS type, and all PSS parameters.

Generator Type Time Constants (Sec.) and Parameters

============== ======== ==================================================================================================

PSS1A KS VSTmax VSTmin VTmin TDR A1 A2 T1 T2 T3 T4 T5 T6

PSS2A KS1 KS2 KS3 VSTmax VSTmin VTmin TDR Tw1 Tw2 Tw3 Tw4 N M T1

ID T2 T3 T4 T5 T6 T7 T8

-------------- -------- ------- ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------

Gen1 PSS1A 3.150 0.900 -0.900 0.000 0.200 0.000 0.000 0.760 0.100 0.760 0.100 1.000 0.100



Induction Machine Data This section contains the information for all dynamically modeled induction machines in the system, including machine ID, connected bus ID, rated kV and MVA, model type and model parameters, load model and model parameters, inertia, initial MW and Mvar loading, and slip.

Conned Bus Ind. Motor Rating (base) Eqiv. Model (%Z & seconds) CKT or Double Cage Models (% impedance)

============ ================ ============== =========================== ================================================

Bus ID Machine ID MDL kV MVA Ra Xlr Xoc Tdo' Rs Xs Xm Rrfl,1 Rrlr,2 Xrfl,1 Xrlr,2

------------ ------------ --- ------ ------- ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------

Bus3 Mtr2 CKT2 13.200 0.649 3.83 10.29 365.20 1.52 1.23 11.67 9.30

Sub3 Swgr Pump 1 CKT1 4.000 0.434 3.83 19.36 375.50 0.81

Conned Bus Ind. Motor H(sec) Load Model Normal Loading

============ ============ ====== ================================================ ==============================

Bus ID Machine ID H Model ID A0 A1 A2 A3 % Slip MW Mvar % Load

------------ ------------ ------ ------------ ------ ------ ------ ------ ------ ------ ------ ------

Bus3 Mtr2 0.310 a k***3 0.00 0.00 100.00 0.00 1.41 0.599 0.297 0.0

Sub3 Swgr Pump 1 0.200 FAN 10.00 -91.00 321.00 -147.00 1.18 0.400 0.188 30.0

Initial Load Flow Report An initial load flow study is performed to determine all initial settings for machines, exciters/AVRs, and governors/turbines with the specified initial loading condition. The initial load flow result is printed for you to inspect the system pre-event operating conditions. The format for the initial load flow report is similar to those of the load flow output report and thus a sample printout is omitted. Load Flow Report @ T=*.* This is the load flow report prior to the occurrence of a specified event. Following this section should be a detailed list of actions for the event. Note that for each event, there will be a corresponding pre-event load flow report. The format of this section is similar to those of the load flow output report and thus a sample printout is omitted.

Event/Action Data This section lists detailed information on each action included in an event. This section appears right after a load flow report performed before this event and its associated actions occur.

Bus / Machine Revision (Modification)

=====================================

Bus/Mach ID Existing Type New Type

------------ ------------- ----------

Main Bus Swing Bus Faulted

This page indicates bus/machine revisions occurring at simulation time T = 0.1000 seconds.

Final Load Flow Report This is the load flow reported for the time at the end of the simulation. Formats of this section are similar to those of the load flow output report and thus a sample printout is omitted.



Tabulated Simulation Result This section tabulates, for each device that is selected for tabulation in the study case, the simulation results as functions of time at the specified plot time step. The type of tabulated results is the same as the plot curves, as defined in Plot Options.

Gen. (Gen1 ) Syn. MT (Syn1 ) Syn. MT (Syn4 )

====== ================================== ================================== ==================================

Time Ang. Freq. Mech. Elec. Term. Ang. Freq. Mech. Elec. Term. Ang. Freq. Mech. Elec. Term.

(Sec.) (deg) (Hz) (MW) (MW) I (A) (deg) (Hz) (MW) (MW) I (A) (deg) (Hz) (MW) (MW) I (A)

------ ----- ----- ----- ----- ------ ----- ----- ----- ----- ------ ----- ----- ----- ----- ------

0.000 30.92 60.00 6.34 6.30 265.1 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.020 30.92 60.00 6.34 6.30 265.1 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.040 30.91 60.00 6.34 6.30 265.0 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.060 30.91 60.00 6.34 6.30 265.0 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.080 30.91 60.00 6.34 6.30 265.0 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.100 30.90 60.00 6.34 6.30 264.9 -27.60 60.00 0.99 0.99 48.9 -55.88 60.00 2.76 2.77 123.6

0.101 30.90 60.01 6.34 0.53 1202.6 -27.60 59.99 0.99 0.37 328.9 -55.87 59.98 2.76 -0.79 834.8

0.121 31.92 60.28 6.34 0.48 998.3 -28.86 59.62 0.98 0.37 231.1 -58.01 59.35 2.73 -0.30 495.4

0.141 35.00 60.57 6.34 0.51 908.8 -32.82 59.26 0.97 0.42 233.1 -64.69 58.73 2.69 -0.31 491.0

0.161 40.15 60.86 6.33 0.56 877.5 -39.25 58.93 0.97 0.49 235.3 -75.83 58.12 2.65 -0.29 485.6

0.181 47.31 61.13 6.32 0.61 869.6 -47.87 58.65 0.96 0.55 239.0 -91.32 57.52 2.62 -0.26 479.2

0.201 56.39 61.38 6.30 12.44 756.5 -58.48 58.44 0.96 4.33 264.8 -111.07 56.99 2.58 9.23 837.0

0.221 64.76 60.91 6.26 15.28 756.7 -65.16 59.93 0.99 4.22 195.3 -127.85 58.58 2.67 11.12 689.2

0.241 69.21 60.32 6.21 16.48 769.4 -60.51 61.48 1.02 3.89 176.2 -132.76 60.20 2.77 10.88 706.9

0.261 69.32 59.72 6.16 16.13 732.8 -45.69 62.64 1.04 2.69 117.3 -126.29 61.73 2.85 10.58 656.7

0.281 65.30 59.19 6.10 14.40 639.6 -24.93 62.99 1.04 0.73 35.6 -109.13 63.14 2.93 9.59 533.6

0.301 57.95 58.80 6.05 11.67 508.4 -5.05 62.29 1.03 -1.25 54.2 -82.88 64.16 2.98 6.56 331.3

0.321 48.44 58.59 6.02 8.53 366.8 6.90 60.79 1.01 -2.35 99.7 -51.73 64.33 2.99 1.22 105.3

TS Action Summary This section lists all the actions in the study, including both specified in the Transient Stability Study Case Editor and those initiated by relay actions.

Device Action Time

============ ========== ========

Main Bus Faulted 0.100

Main Bus Normal 0.200


Transient Stability Analysis One-Line Diagram Displayed Results

17.7 One-Line Diagram Displayed Results In addition to the text report, PowerStation displays the transient stability calculation results on the one-line diagram.

Transient Stability Time-Slider Once a transient stability study is completed, a Transient Stability Time-Slider, as shown below, will appear next to the Configuration & Mode Toolbar. The slider ranges from zero to the total simulation time. Initially, the reference pointer is at the far left, corresponding to t = 0 seconds. You may click on either end of the ruler to move the pointer one grid at a time, or hold the mouse button down to move the pointer continuously. You may also click on the pointer, hold the mouse button down, and then drag the pointer to the desired position. The time corresponding to the pointer position is also displayed next to the ruler in units of seconds. As you move the pointer along the slider, the displayed results change accordingly, providing you with a quick way to examine the calculation results.

The one-line diagram displays are only available for those devices that are selected for plot options. Depending on the device type, different calculation results are displayed as defined below:

Buses • Voltage – bus voltage magnitude in kV or percent • Frequency – bus frequency in Hz or percent

Syn. Generators • Power Angle – synchronous generator rotor angle in degree or radian • Frequency – synchronous generator frequency in Hz or percent • Efd – synchronous generator field voltage in per unit • Real and Reactive Power – synchronous generator electrical power generation in kW+jkvar or

MW+jMvar • Apparent Power – synchronous generator electrical power generation in kVA or MVA • Current – synchronous generator terminal current in Amp

Syn. Motors, MV • Power Angle – synchronous motor rotor angle in degree or radian • Frequency – synchronous motor frequency in Hz or percent • Voltage – synchronous motor terminal voltage in kV or percent • Real and Reactive Power – induction machine electrical power loading in kW+jkvar or MW+jMvar • Apparent Power – induction machine electrical power loading in kVA or MVA • Current – induction machine terminal current in Amp



Syn. Motors, LV • Power Angle – synchronous motor rotor angle in degree or radian • Frequency – synchronous motor frequency in Hz or percent • Voltage – synchronous motor terminal voltage in kV or percent • Real and Reactive Power – induction machine electrical power loading in kW+jkvar or MW+jMvar • Apparent Power – induction machine electrical power loading in kVA or MVA • Current – induction machine terminal current in Amp

Ind. Machines, MV • Speed – induction machine speed in RPM or percent slip • Voltage – induction machine terminal voltage in kV or percent • Real and Reactive Power – induction machine electrical power loading in kW+jkvar or MW+jMvar • Apparent Power – induction machine electrical power loading in kVA or MVA • Current – induction machine terminal current in Amp

Ind. Machines, LV • Speed – induction machine speed in RPM or percent slip • Voltage – induction machine terminal voltage in kV or percent • Real and Reactive Power – induction machine electrical power loading in kW+jkvar or MW+jMvar • Apparent Power – induction machine electrical power loading in kVA or MVA • Current – induction machine terminal current in Amp

MOV • Real and Reactive Power – mov electrical power loading in kW+jkvar or MW+jMvar • Apparent Power – mov electrical power loading in kVA or MVA • Current – mov terminal current in Amp The units for the displayed results are defined in the Results Page of the Transient Stability Display Options. The following is a sample of one-line diagram display from the Transient Stability study.




Transient Stability Analysis Plots

17.8 Plots PowerStation also provides simulation plots for you to examine Transient Stability calculation results in a graphic form. To view the plots, click on the Transient Stability Plots button on the Transient Stability Toolbar. It will bring up a dialog box for the Transient Stability Plot Selection, as shown below, from which you can specify the devices and types of plots to view.

Device Type Select a device type for plotting.

Device ID From this list, select the devices (up to 16 devices at a time) to be plotted. This list contains the devices that have been selected for plots from the study case editors.

Plot Type Check plot type(s) for plot. Different device types have different plot types.

Syn. Generators • Power Angle – synchronous generator power angle in degree • Frequency – synchronous generator frequency in Hz • MWm – synchronous generator shaft mechanical power generator in MW • MWe – synchronous generator electrical power generation in MW • Current – synchronous generator terminal current in Amp • Efd – synchronous generator field voltage in per unit • Ifd – synchronous generator field current in Amp • Machine Z – synchronous generator terminal impedance in % on machine base



Syn. Motors, MV (medium voltage motors) • Power Angle – synchronous motor power angle in degree • Frequency – synchronous motor frequency in Hz • MWm – synchronous motor mechanical power in MW • MWe – synchronous motor electrical power in MW • Current – synchronous motor terminal current in Amp • Voltage – synchronous motor connected bus voltage in % of the bus nominal kV • Machine Z – synchronous motor terminal impedance in % on machine base Syn. Motors, LV (low voltage motors) • Power Angle – synchronous motor power angle in degree • Frequency – synchronous motor frequency in Hz • MWm – synchronous motor mechanical power in MW • MWe – synchronous motor electrical power in MW • Current – synchronous motor terminal current in Amp • Voltage – synchronous motor connected bus voltage in % of the bus nominal kV • Machine Z – synchronous motor terminal impedance in % on machine base

Ind. Machine, MV (medium voltage machines) • Slip – induction machine slip in % • Accel Torque – induction machine acceleration power in MW • MWm – induction machine mechanical power in MW • MWe – induction machine electrical power in MW • Current – induction machine terminal current in Amp • Voltage – induction machine connected bus voltage in % of the bus nominal kV • Machine Z – induction motor terminal impedance in % on machine base

Ind. Machine, LV (low voltage machines) • Slip – induction machine slip in % • Accel Torque – induction machine acceleration power in MW • MWm – induction machine mechanical power in MW • MWe – induction machine electrical power in MW • Current – induction machine terminal current in Amp • Voltage – induction machine connected bus voltage in % of the bus nominal kV • Machine Z – induction motor terminal impedance in % on machine base

Buses • Voltage Angle – bus voltage angle in degree • Frequency – bus frequency in % of system frequency • MW – bus real power loading in MW • Mvar – bus reactive power loading in Mvar • Voltage/Hz – bus voltage per Hz in volt/Hz • Voltage – bus voltage magnitude in % of the bus nominal kV



MOVs • Slip – MOV slip in percent • Acce l Power – MOV acceleration power in kvar • kvar – MOV reactive power loading in kvar • kW – MOV real power loading in kW • Current – MOV current in Amp • Voltage – MOV terminal voltage in % of the connected bus nominal kV base Note that for synchronous motors and induction machines, terminal voltages are also displayed on the one-line diagram. The following is a set of sample plots from the Transient Stability study:

Combine Plots Curves for the selected item will be plotted on the same graph. Multiple scales will be used.


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