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ETAP PowerStation 4.0

User Guide

Copyright 2001 Operation Technology, Inc.

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Operation Technology, Inc. 27-1 ETAP PowerStation 4.0

Chapter 27

Underground Raceway Systems

Cable derating analysis is an important part of power system design and analysis. For designing a new system, it determines the proper size of cables to carry the specified loads. For analysis of an existing system, it examines cable temperatures and determines their ampacities.

Underground Raceway Systems Overview


PowerStation provides five types of calculations for cable derating analysis, namely, steady-state temperature calculation, uniform-ampacity cable ampacity calculation, uniform-temperature cable ampacity calculation, cable sizing, and transient temperature calculation. The steady-state temperature calculation, cable ampacity calculation, and cable sizing are based on the NEC accepted Neher-McGrath method. The transient temperature calculation is based on a dynamic thermal circuit model. All of the calculations can handle multi-raceway systems and consider the effect of heat generated by neighboring cables and external heat sources. This chapter contains the following sections: • The GUI section explains the various toolbars and their functions, how to launch calculations, open

and view an output report, and how to select display options. • The Editor section explains how to add/edit elements of the system, how to create a new study case,

what parameters are required to specify a study case, and how to set them. • The Display Options section explains what options are available for displaying some key system

parameters and the output results on the UGS diagram, and how to set them. • The Calculation Methods section briefly describes calculation methods for steady-state temperature

calculation, cable ampacity calculation, cable sizing, and transient temperature calculation. • The Required Data section describes what data is necessary to perform Cable Ampacity Derating

calculations and where to enter them. • The Output Reports and Plots section illustrates and explains the data contents of the output report

and how to interpret results on the plots. • The Tutorial section provides an overview of the operation and of some key functions of the

Underground Raceway Systems module.

Underground Raceway Systems GUI


27.1 Underground Raceway Systems GUI The UGS presentation is conceptually a cross-section of desired raceways, conduits/locations, cables, and heat sources, which are in the same vicinity. The UGS presentation allows you to graphically arrange raceways, conduits, cables, and external heat sources to represent cable routing and to provide a physical environment to conduct cable ampacity derating studies. Each UGS presentation is a different cross-section of the underground system. This is a different concept than the multi-presentation of the one-line diagram, where all presentations have the same elements.

You can create as many UGS presentations as you wish. There is no limit on the number of raceways and heat sources that can be created/added in one presentation. In UGS, each presentation acts independently. If you add a raceway to a UGS presentation, this raceway will not be shown in the other UGS presentations. However, raceways from any UGS presentation can be added to the other UGS presentations as existing raceways. Also, if you delete a raceway from a UGS presentation into the Dumpster, this raceway can be added to other UGS presentations as an existing raceway.

27.1.1 Create a New UGS Presentation When a new project is created, by default, no UGS presentation is created. You need to create UGS presentations when necessary. To create a UGS presentation, right-click on U/G Raceway System in the Project View, then click on Create New.

Creating A UGS Presentation



A graphical user interface window with a UGS presentation will be displayed on your screen. The ID (name) of the displayed presentation is UGS1 by default (default name appended with a number). The name may be changed to any unique name (maximum 12 characters) that you choose. To change the name, double-click on the UGS1 presentation. This will open its editor.

Change ID (Name) of a UGS Presentation

Another way you can change the name of a UGS presentation is to right-click on UGS1 in the Project View, then click on Properties, as shown below. Enter a new name from the dialog box.

Right-Click On UGS1, to View, Save, Rename, or Purge UGS1



27.1.2 Edit Toolbar

UGS Edit Toolbar

Pointer The mouse pointer allows you to select or move items. Clicking on the Pointer icon returns the cursor to its original shape after an element icon has been clicked on, displaying an element to be placed into the UGS.

Existing External Heat Source Click on the Existing External Heat Source icon to open a drop-down list from which you can choose an external heat source that has been previously created.

A message will appear if no existing external heat sources are available. These external heat sources can be found either in the Dumpster or in other U/G Systems. For more information on external heat sources see the External Heat Source Editor.

New External Heat Source Click on the New External Heat Source icon to create a new external heat source. This will enable you to place it in the UGS wherever there is space available. For more information on external heat sources see External Heat Source Editor.

Add Existing Heat Sources

Add Existing Cables

Add Existing Duct Bank RWs

Add Existing Direct Buried RWs

Add New Conduits for Duct Banks RWs

Display Options

Add New Heat Sources Add New Cables Add New Duct Bank RWs Add New Direct Buried RWs Add New Locations for Direct Buried RWs



Existing Cable Click on the Existing Cable icon to open a drop-down list from which you can choose a cable that has been previously created. This list includes one-line, equipment, and UGS cables.

The cables in this list can be found in the one-line diagram (either as a one-line or equipment cable), Dumpster (deleted cables), or in other U/G raceway systems (UGS cables). Cables selected from the one-line diagram will be converted from one-line or equipment cables to compound cables. A compound cable represents a cable that exits in the one-line diagram and UGS. For more information on cables, see the Cable Editor Overview. Note that you can graphically add existing one-line cables to any location (conduit) in UGS. To do this, press and hold Control+Shift and drag the cable, using the mouse, from the one-line diagram into a location in UGS. A message will appear if no existing cables are available. These cables can be found in the one-line diagram, Dumpster, or in other U/G Systems. Cables selected from the one-line diagram will be converted from one-line cables to compound cables. For more information on cables see the Cable Editor Overview.

New Cable Click the New Cable icon to create a new cable. This will enable you to place it in the UGS wherever there is space available. This cable will be a UGS cable since it only exists in the UGS. To add this cable (or any other cable in the UGS) to the one-line diagram press and hold Control+Shift and drag the cable, using the mouse, from the UGS into the one-line diagram. For more information on cables see the Cable Editor Overview.

Existing Duct Bank Raceway Click the Existing Duct Bank Raceway icon to open a dialog box from which you can choose a duct bank raceway that has been previously created.

A message will appear if no existing duct bank raceways are available. These duct bank raceways can be found either in the Dumpster or in other U/G Systems. For more information on duct bank raceways see Duct Bank Raceway Editor.



New Duct Bank Raceway Click the New Duct Bank Raceway icon to create a new duct bank raceway. This will enable you to place it in the UGS wherever there is space available. For more information on duct bank raceways see Duct Bank Raceway Editor. Existing Direct Buried Raceway Click the Existing Direct Buried Raceway icon to open a dialog box from which you can choose a direct buried raceway that has been previously created.

A message will appear if no existing direct buried raceways are available. These direct buried raceways can be found either in the Dumpster or in other U/G Systems. For more information on direct buried raceways see the Direct Buried Raceway Editor section.

New Direct Buried Raceway Click the New Direct Buried Raceway icon to create a new direct buried raceway. This will enable you to place it in the UGS wherever there is space available. For more information on direct buried raceways see the Direct Buried Raceway Editor section.

New Conduit Click the New Conduit icon to create a new conduit. This will enable you to place it in any duct bank raceway wherever there is space available. For more information on conduits see Conduit Editor.

New Location Click the New Location icon to create a new location. This will enable you to place any Direct Buried Raceway wherever there is space available. For more information on locations see the Location Editor section.

Display Option Click on the Display Options icon to change the appearance of element IDs and ratings in the UGS. For more information, see the Display Options section.

Underground Raceway Systems Study Toolbar


27.2 Study Toolbar

Steady-State Cable Temperature Calculation Click on this icon to calculate the steady-state temperature of cables in the raceway system under the specified loading conditions. PowerStation uses the NEC accepted Neher-McGrath method for these calculations. It determines steady-state conductor temperature for the specified cable loading and raceway system configuration, considering the effect of heat generated by neighboring cables and external heat sources.

Uniform-Ampacity Cable Ampacity Calculation Click on this icon to calculate cable ampacity under uniform ampacity conditions for all cables in the raceway system. This calculation assumes that the loading of all cables is increased/decreased uniformly based on cable base ampacity, which is defined in the cable library. The cable ampacity is calculated by increasing the loading of all cables until the temperature of the hottest cable reaches the maximum allowable limit. PowerStation uses the Neher-McGrath method for this calculation.

Uniform-Temperature Cable Ampacity Calculation Click on this icon to calculate cable ampacity under uniform temperature conditions for all cables in the raceway system. This calculation adjusts individual cable loading to maintain uniform temperature throughout the raceway system. The cable ampacity is obtained when the cable temperature reaches its maximum allowable limit. PowerStation uses the Neher-McGrath method for this calculation.

Steady-State Cable Temperature Calculation

Cable Ampacity Calculation, Uniform-Ampacity

Cable Ampacity Calculation, Uniform-Temperature

Cable Sizing

Transient Cable Temperature Calculation

Display Options

View Output Report

Cable Temperature Plots

Halt Current Calculation

Get On-Line Data

Get Archived Data

Underground Raceway Systems Study Toolbar


Cable Sizing Click on this icon to automatically optimize cable sizes for the specified cable loading and cable temperature limit. The result of this study yields the smallest possible sizes for all cables in the raceway system that can carry the specified loading within the temperature limit. PowerStation uses the Neher-McGrath method for this calculation.

Transient Cable Temperature Calculation Click on this icon to calculate cable transient temperatures as a function of time. The cables carry time-varying loads, as defined in the Load Profile of the Cable Editor. This study allows you to investigate cable transient operating conditions and verify cable temperatures against time for determining the short-time loading limit. This calculation is based on a dynamic thermal circuit model.

Display Options Click on this icon to open the Cable Derating Display Options dialog box to display calculation results.

View Output Report To view the contents of the last output report, click on the View Output File button on the toolbar. The output file name is displayed on the Study Case Toolbar. You can also view output reports by clicking on the View Output File button on the Study Case Toolbar. A list of all output files in the selected project directory is provided for cable ampacity derating calculations. To view any of the listed output reports, click on the output report name, and then click on the View Output File button.

The output reports for cable derating studies have a .cdr 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. The text 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 recommended settings that are explained in the Printing and Plotting chapter.

Cable Transient Temperature Plot Click on the Plot icon to select and plot the calculated temperatures of the cables in the raceway.

Get On-Line Data If the ETAP key installed on your computer has the on-line feature (PSMS), you can copy the on-line data to the cables in the current U/G system. Get Archived Data If the ETAP key installed on your computer has the on-line feature (PSMS), you can copy the archived data to the current U/G system.

Underground Raceway Systems Study Case Editor


27.3 Study Case Editor

The Cable Derating Study Case Editor contains solution control variables, cable loading parameters, and options for output reports. PowerStation allows you to create and save an unlimited number of study cases. Cable derating calculations are conducted and reported in accordance with the settings you have specified in the study case editor. Note that you can have an unlimited number of study cases and can easily switch between the 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. To conduct studies, you first need to switch to the calculation mode by clicking on the U/G Cable Raceways button on the Mode Toolbar.

The Cable Derating Study Case Editor can be accessed by clicking on the Study Case button located on the Study Case Toolbar. You can also access this editor from the Project View by clicking on the Cable Derating Study Case folder.



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

Study Case ID Study case ID is shown in this entry field. Here you can rename a study case by deleting the old ID and entering the new ID. The study case ID can be up to 25 alphanumeric characters. Use the Navigator button at the bottom of the editor to move between study cases.

Initial/Steady-State Amp Here you can specify the cable loading for the study case. The loading amps are entered into the Loading page of the Cable Editor. Note that the cable current specified in the Cable Editor is the phase current, and the current each conductor carries is equal to the phase current divided by the number of conductors per phase.

Load Profile When this option is selected, the first current value in the Transient Load Profile list in the Loading page of the Cable Editor will be used as the initial load current for the transient temperature calculation, and as the load current for the steady-state temperature calculation.

Operating Load When this option is selected, the operating load in the Loading page of the Cable Editor will be used as the initial load current for the transient temperature calculation and as the load current for the steady-state temperature calculation. Note that operating load current can be updated with the load flow calculation result by clicking on the Update Cable Load Current button on the Load Flow Tool Bar.

Multiplication Factor ETAP PowerStation provides several multiplication factors, which allow you to vary the cable loading both individually and globally. These options furnish flexibility in raceway system design and allow you to project future load variation.



Global Projection MF The cable load, which you have specified in the Cable Editor, is multiplied by this factor prior to calculation, allowing you to globally change the system load.

Use Individual Projection MF Select this option to apply the individual load projection multiplication factor that you have entered in the Loading page of the Cable Editor. The cable load will be multiplied by this factor prior to calculation.

Use Application MF When this box is checked, the Application MF selected in the Ampacity page of the Cable Editor will be utilized to modify the cable load. Prior to performing the cable derating calculation, the cable load current is multiplied by the Application MF.

Transient Temperature Study Enter the time limit and plot time step for a cable transient temperature study in this section.

Max. Time Maximum Time is the length of time, at the unit selected, for which the transient temperature calculation will be performed.

Output Step Size Output Step Size specifies the time step, at the unit selected, at which plot points will be generated. The total number of plot points generated is approximately equal to the Max. Time divided by the Output Step Size.

Unit The Unit selection box allows you to select time units for the Max. Time and Output Step Size. Time unit selections include days, hours, minutes, and seconds.

Update This section is provided for you to flag PowerStation to update your cable data.

Currents from Ampacity Calculation If the box is checked, after running a UT ampacity or UA ampacity calculation, PowerStation will update the allowable current for each cable involved with the calculated ampacity.

Size from Cable Sizing Calculation If the box is checked, after running a cable sizing calculation, PowerStation will update all the cables involved with the calculated optimal size.

Underground Raceway Systems Display Options


27.4 Display Options for UGS

27.4.1 Cable Derating Result Display Options This dialog box allows you to specify the format for information annotations associated with an Underground Raceway presentation.

Default This check box is used to edit the display options specified by the Project Default Display Options. When this option is selected, the Info section in this dialog box will be disabled and all the customized selections displayed will be ignored and replaced by the default settings.

Info This section becomes accessible only when the Use Default Display Options box is not checked; otherwise, the information in this section will not apply.

Color This selection box allows you to select one of the sixteen available colors for information annotations.

Cable ID Select the check box to display the cable ID in the raceway view.

Conduit/Location ID Select the check box to display the conduit/location ID in the raceway view.

Raceway ID Select the check box to display the raceway ID in the raceway view.

Heat Source ID Select the check box to display the external heat source ID in the raceway view.



27.4.2 U/G Raceway Display Options This dialog box is used to specify the format and content of the annotations to be displayed for each individual element on the UGS presentation.

Default If the Use Project Default Options box is selected, the project default settings will be used on the UGS presentation.

Options

Color Select from a variety of colors to display annotations for each element.

ID For each element type (cable, conduit/location, raceways, and heat sources) choose whether or not to display their ID in the UGS presentation.

Size For each element type (conduit/location, raceways, and heat sources) choose whether or not to display their size (in inches or cm) on the UGS presentation.



27.4.3 Default Display Options - UGS This dialog box is used to specify the default format and content of the annotations to be displayed for each individual element on UGS presentations.

Underground Raceway System Annotations

Color Select the color for information annotations to be displayed.

ID For each element type (cable, conduit/location, raceways, and heat sources) choose whether or not to display their ID on the UGS presentation.

Size For each element type (conduit/location, raceways, and heat sources) choose whether or not to display their size (in inches or cm) on the UGS presentation.

Annotation Font

IDs Select the font, style, and size to display all IDs selected in Display Options.

Ratings Select the font, style, and size to display all ratings selected in Display Options.

Results Select the font, style, and size to display all study results selected in their respective Display Options.

Underground Raceway Systems Edit A UGS


27.5 Edit A UGS This section addresses editors for elements in the U/G Raceway Systems (UGS). Except for the element’s ID, all other data that appear in the editors are considered engineering properties. The elements that are included in this chapter are shown below. Underground System Raceway External Heat Source

Add Elements Duct bank raceways and direct buried raceways, conduits for duct bank raceways, locations for direct buried raceways, external heat sources, and cables are the elements available for adding to an underground raceway system which can be done by clicking on the Edit Toolbar. Rules • Elements can be added ONLY in Edit mode when the Base Data is active. • Elements CANNOT be added when you are in study mode or in a Revision level of the database. • You CANNOT drop two raceways on top of each other. • You CANNOT drop an external heat source inside a raceway. • Cables can ONLY be placed inside of a conduit or location. • Conduits and locations can ONLY be added inside of their respective raceway types. • Conduits and raceways CANNOT overlap each other.



A UGS Presentation

To add a new element to your UGS presentation, select a new element from the Edit Toolbar, which changes the cursor symbol to a picture of that element. You may place the element anywhere in the UGS (where there is room) by clicking the mouse. After dropping the element, the cursor goes back to its original arrow shape. If you double-click on an element in the Edit Toolbar, you can place multiple copies of the same element in the UGS. To add an existing element to a UGS presentation, select an existing element in the Edit Toolbar (red symbols), which changes the cursor shape to a picture of that element. Move the cursor into the UGS presentation and click. It will open an editor (dialog box), which allows you to select an element from the list box to be added as an existing element, and then click on OK. The element will be added with the same ID (name) with all of the engineering properties preserved.

External Heat Source Cable Duct Bank Raceway Direct Buried Raceway

Dialog Boxes for Adding Existing Elements to UGS Presentations

Add Raceways and External Heat Sources Click on the Raceway or External Heat Source button on the Edit Toolbar, move the cursor to the UGS presentation, and drop it into place by clicking. If a new raceway or heat source is selected from the toolbar, PowerStation creates the new raceway or external heat source using the default values. If an existing raceway or heat source is selected, PowerStation prompts you with a drop-down list to select an element from the already existing ones.

Add Cables Click on the Cable button on the Edit Toolbar, move the cursor inside of a conduit or location, and drop it into place by clicking. If you select new cables from the toolbar, a new cable (UGS cable) is created with a dummy cable diameter. If an existing cable is selected, PowerStation provides a drop-down list to select from. You can select a one-line cable, equipment cable, or UGS cable.

Add Conduits Click on the Conduit button on the Edit Toolbar, move the cursor inside of a duct bank raceway, and drop it into place by clicking. Conduits are always created. You cannot add existing conduits to a raceway. The drop point of a conduit or location is its center. The cursor is marked with an X if your drop point is too close to the raceway’s edge causing it to overlap the outside of the raceway.



Add Locations Click on the Location button on the Edit Toolbar, move the cursor inside of a direct buried raceway, and drop it into place by clicking. Locations are used for placing and locating cables in direct buried raceways and do not physically exist. Locations are always created. You cannot add existing locations to a raceway. The drop point of a location is its center. The cursor is marked with an X if your drop point is too close to the raceway edge causing it to overlap outside of the raceway.

Add One-Line Cables You can graphically add cables from one-line diagrams (one-line cables) to underground raceways. To do this from a one-line diagram presentation, use <Ctrl><Shift>+Drag to select and graphically drag a one-line cable to a conduit or location in a UGS presentation. At first, the cursor becomes a cable symbol with a big X marked on top of it. Once the cursor inside a conduit or location, the X disappears and you can drop it. The cable that you have just placed inside a U/G raceway appears both in the one-line diagram and the UGS presentations. The property of this cable can be changed from either presentation. Note that you can also use <Ctrl><Shift> + Drag to add UGS cables to the one-line diagram.

Select Elements To select an element, click the left mouse button while the cursor (arrow shape) is on top of the element. To rubber-band multiple raceways, click the left mouse outside the raceway and drag the mouse across the raceways you want to select. It will show you a dotted rectangle. When the mouse is released, only the raceways inside the rectangle will be selected. Note that when a raceway is selected, no matter how many conduits, locations, or cables it contains, the raceway is considered to be one element. For example, if you cut or copy a selected raceway, the raceway and its contents will be cut or copied.

Selecting & Deselecting Multiple Elements <Ctrl>Click on the elements that you want to select or deselect. Move / Relocate Elements When an element (other than a cable) is added to a UGS presentation, according to the drop point, its coordinates (x and y) are updated automatically in its editor and in the Help line at the bottom of your screen. You may relocate the element to new coordinates, either from its editor (Ref. X and Ref. Y for raceways and external heat sources, and Horiz. Dist. and Vert. Dist. for conduits and locations relative to their raceways reference point) or by dragging the element and watching the Help line change to the desired position, as shown below.

X and Y coordination of an element in the Help Line

To drag an element, first select the element that you want to move, place the cursor on top of the selected element. Click and hold the left mouse button, drag the element to the desired position, and release the left button.

Move Raceways, Heat Sources, and Locations (Conduits) Select the element, hold the left button, drag it to the new position, and then release the left button. When the cursor is placed on a selected element, the cursor becomes a movement symbol.



The following graph shows the relationship between raceway reference points and other elements.

The value of the reference Y for raceways and heat sources represents the depth of the elements below the earth’s surface. The value of the reference X determines the relative horizontal distance between raceways and heat sources. For a UGS presentation that has only one raceway, the reference X is irrelevant. Rules • Elements CANNOT be relocated in study mode or in a Revision level of the database. • Elements CANNOT be overlapped. • All three phases of a cable must be routed through the same raceway, i.e., if you move one of the

conductors, PowerStation prompts you to move all conductors (placed together). You can also move a raceway (reference X and Y) or a location/conduit (horizontal and vertical distance) from its editor as shown below.



Move Cables You can graphically move any cable within a UGS. To move a cable, select the cable, hold the left button, drag it to the new location (conduit), and then release the left button. When you move a cable from one raceway to another raceway, all conductors for that cable will be moved.

Move Cable2 from One Conduit to Another

Move Cable4 from Raceway RW1 to RW2

Cut (Delete) Elements When elements are cut, they are placed into the Dumpster (inside a Dumpster Cell). To cut an element that is selected, click on the Cut button in the Project Toolbar or press Delete on the keyboard. You can cut elements in Edit mode only. When you cut an element or group of elements, they are deleted from UGS and placed in the Dumpster with the same IDs (engineering properties are preserved). Elements can be cut (deleted) three ways. • Click on Edit in the menu bar, and then click on Cut. • Click on the Cut button on the Project Toolbar. • Press the Delete key on the keyboard.



Rules • Elements can be cut in Edit mode ONLY when Base Data is active. • Elements have to be selected in order for them to be Cut (deleted). • When a conduit or location that contains cables is cut, the cables are not deleted. They are moved

into a container attached underneath of the raceway. This container is used to hold cables that belong to this raceway but are not assigned to a specific conduit or location.

• When one or more raceways, cables, or heat sources are placed in the Dumpster, PowerStation forms a new Dumpster Cell (element group) that holds these elements. PowerStation automatically assigns the name of the Dumpster Cell.

Copy Elements Elements are copied into the Dumpster (inside a Dumpster Cell). To copy an element or group of elements, place the mouse on top of the element, click the right mouse button, and then select Copy. When you copy an element or group of elements, they get copied into the Dumpster with new IDs while the engineering properties are preserved. Elements can be copied two ways: • Click on Edit in the menu bar, and then select Copy. • Click on the Copy button in the Project Toolbar. Rules • Element can be copied in Edit mode ONLY when Base Date is active. • Element must be selected before they can be copied. • When one or more raceways, cables, or heat sources are placed in the Dumpster, PowerStation forms

a new Dumpster Cell (element group) that holds these elements. PowerStation automatically assigns the name of the Dumpster Cell.

To graphically copy raceways from a UGS presentation to the Dumpster, use <Shift>+Drag. After you select a raceway, hold the <Shift> key down, and click and hold the left mouse button down while you drag the mouse. At first, the cursor becomes a preventive symbol (a red circle with a line across it). When you move the cursor on top of the Dumpster, it becomes a box symbol with a plus sign indicating that you can copy it to the Dumpster. Paste Use the Paste command to copy the selected cell from the Dumpster into the UGS presentation. To paste a copy of the elements from a Dumpster Cell, first select the Cell from the Dumpster, activate the UGS presentation view you want the element to be pasted into, and then click on Paste. When you paste elements, they get copied into the UGS presentation with new IDs (engineering properties are preserved). Elements can be pasted two ways: • Click on Edit in the menu bar, and then select Paste. • Click on the Paste icon in the Project Toolbar.



Rules • Pasting CANNOT be done if there are no Cells (element groups) in the Dumpster. • Pasting can be done in Edit mode ONLY when Base Data is active. • In the Dumpster, conduits or locations CANNOT be deleted or purged unless the raceway containing

these conduits or locations is deleted or purged. • You can paste any Dumpster Cell you desire by making it active from the Dumpster presentation. • When you cut or copy elements to the Dumpster, the newly created Dumpster Cell becomes the

active Cell. • You CANNOT paste part of a Dumpster Cell; the entire contents of a Cell are pasted. • You CANNOT paste Dumpster Cells that contain one-line diagram elements in UGS presentations. • A UGS presentation can contain multiple raceways, but not a duplicate raceway, i.e., a raceway

CANNOT be placed twice in the same UGS presentation.

Size Elements When an element is added into a UGS presentation, its size is set to the default. You can graphically change the width and height of raceways, as well as, the outside diameter of conduits, locations, and heat sources. To change the size, select the element, move the cursor to the corner or edges of the selected element, and, when the cursor changes its shape, release the mouse button. You can see the new sizes on the Help Line. Note that you can also change the sizes from the raceway editor. Outside diameter (OD) of cables can only be changed from the Cable Editor. Rules • Sizing elements can be done in Edit mode ONLY when Base Data is active. • Elements CANNOT overlap each other.

Underground Raceway Systems Underground System Editor


27.6 Underground System Editor The Underground System (UGS) Editor provides details regarding the overall layout of the underground system. This includes global properties such as soil type and temperature.

ID Enter a unique alphanumeric ID with a maximum of 25 characters. PowerStation automatically assigns a unique ID to each UGS. The IDs consist of the word UGS plus an integer starting with the number one and increasing with the addition of each UGS. The default ID can be changed from the Defaults menu in the menu bar or from the Project View.

Soil Soil refers to the surrounding earth for the raceway system. Backfill soil or concrete for raceways is specified in the Raceway Editor.

Type Select the soil type from the drop-down list. • Average Dry • Average Wet • Clay Dry • Clay Wet • Sandy Dry • Sandy Wet Note that the selection of soil type will not affect the value of RHO.

RHO Enter the thermal resistivity of the earth (soil) in degrees C-cm/Watt.

Underground Raceway Systems Underground System Editor


Temperatures

Ambient Ambient refers to the soil ambient temperature specified in degrees Celsius. The soil temperature is a constant from the surface of the soil to the deepest point considered in the underground raceway system.

Warning Warning refers to the conductor warning temperature specified in degrees Celsius. Each conductor, whose temperature is above the warning level and below the alarm level, will be shown in magenta after a cable temperature calculation study has been performed.

Alarm Alarm refers to the maximum allowable conductor temperature specified in degrees Celsius. Each conductor, whose temperature is above the alarm level, will be shown in red after a cable temperature calculation study has been performed.

Heat Sources This is the list of all external heat sources located in this underground raceway system. Each heat source is specified by an ID as well as its (center-point) X and Y coordinates. X and Y coordinates are specified from the upper left corner of your underground raceway system.

Raceways This is the list of all raceways (direct-buried or duct bank) located in this underground raceway system. Each raceway is specified by its ID, as well as, its reference point X and Y coordinates. The reference point is the upper-left corner of the raceway.

Underground Raceway Systems Raceway Editor


27.7 Raceway Editor The Raceway Editor consists of three separate pages or screens. These are the Raceway, Location, and Cable pages. The Location and Cable pages will not be displayed if there are no conduits/locations or cables in the raceway.

27.7.1 Raceway Page

Raceway Info

ID Enter a unique alphanumeric ID with a maximum of 25 characters. PowerStation automatically assigns a unique ID to each raceway (direct buried or duct bank). The default ID consists of RW plus an integer starting with the number one and increasing as the raceway numbers increase. The default ID can be changed from the Defaults menu in the menu bar or from the Project View.

Ref.X Ref.X is the X coordinate for the reference point in inches or cm. The reference point is the upper left corner of the raceway. X and Y coordinates are specified from the upper left corner of your underground raceway system.

Ref.Y Ref.Y is the Y coordinate for the reference point in inches or cm. The reference point is the upper left corner of the raceway. X and Y coordinates are specified from the upper left corner of your underground raceway system.



Width Width specifies the raceway width in inches or in centimeters. The width of the raceway begins from the raceway reference point and extends to the right.

Height Height specifies the raceway height in inches or in centimeters. The height of the raceway begins from the raceway reference point and extends down.

Fill Type Select the type of fill (material) from the list of options used in the construction of the raceway. Light Aggregate and Heavy Aggregate are options for duct bank raceways, and Average Dry, Average Wet, Sandy Dry, Sandy Wet, Clay Dry, and Clay Wet are options for direct buried raceways.

Fill RHO Fill RHO specifies the thermal resistance of the fill material. Units are specified in degrees Celsius centimeters per Watt.

Cables in Raceway Displays a list of all the cables located in this raceway. Each cable is described with its ID, the number of conductors per phase, the number of conductors per cable, and which location (conduit) the cable is located in.

27.7.2 Location Page

Conduit / Location Info

Conduit Enter a unique alphanumeric ID with a maximum of 25 characters. PowerStation automatically assigns a unique ID to each location or conduit. The default IDs consist of Loc (for direct buried locations) or Cond (for duct bank conduits) plus an integer starting with the number one and increasing as the location / conduit numbers increase. The default ID can be changed from the Defaults menu in the menu bar or from the Project View.



Horiz.Dist Horiz. Dist specifies the horizontal distance of the center point of the location (conduit) from the raceway reference point. The horizontal distance is specified in inches or in centimeters.

Vert. Dist Vert. Dist specifies the vertical distance of the center point of the location (conduit) from the raceway reference point. The vertical distance is specified in inches or in centimeters.

Type (Conduit) Type specifies the type of material used in the fabrication of the conduit for duct bank raceways. This field is not active for direct buried raceways. You can select from a variety of options including: • Metal • Fiber • Transite • PVC-40 • PVC-80 • PVC-A • Other

Size (Conduit) Size specifies the standard diameter of a conduit in inches or centimeters. There are a variety of sizes to choose from including: • 0.50 • 0.75 • 1.00 • 1.25 • 1.50 • 2.00 • 2.50 • 3.00 • 3.50 • 4.00 • 5.00 • 6.00

OD (Conduit) OD specifies the outside diameter of a conduit in inches or centimeters. For standard size conduits, PowerStation provides the outside diameter of the conduit based on the conduit type.

Thickness (Conduit) Thickness specifies the thickness of the material used to fabricate the conduit in inches or centimeters. For standard size conduits, PowerStation provides the conduit thickness based on the conduit size and type.



27.7.3 Cable Page

Cable Type Cable type specifies details regarding the selected cable header and size. The details include manufacturer, type, voltage rating, loading factor, number of conductors per cable, conductor material type, and magnetic or non-magnetic installation type.

Size Size specifies the cable size using international standards. The units for cable sizing are AWG/kcmil for English unit cables and mm2 for Metric unit cables. Note that for quick selection, PowerStation provides the list of all available cable sizes from the selected library. Changing the cable size will update pertinent cable data from the library.

Cable Editor Clicking on the Cable Editor button will open the editor for the selected cable. The Cable Editor contains electrical and physical data used in both the one-line diagram and the underground raceway systems. Any changes made in the Cable Editor will be reflected on the Cable page of the Raceway Editor.

Cable Routing Cable routing specifies the conduit or location where this cable is installed (routed) in every underground raceway system for this project. Details include the raceway ID, the type of raceway, i.e. direct buried or duct bank, and which underground raceway system the raceway is located in.

Underground Raceway Systems External Heat Source


27.8 External Heat Source

External heat sources can be placed in underground raceway systems to simulate steam pipes or other sources of heat in the vicinity of raceways.

Info

ID Enter a unique alphanumeric ID with a maximum of 25 characters. PowerStation automatically assigns a unique ID to each external heat source. The IDs consist of HS plus an integer starting with the number one and increasing as the external heat source numbers increase. The default ID can be changed from the Defaults menu in the menu bar or from the Project View.

Ref. X Ref. X is the X coordinate reference for the focal (center point) of the external heat source in inches or cm. X and Y coordinates are specified from the upper left corner of your underground raceway system.

Ref. Y Ref. Y is the Y coordinate reference for the focal (center point) of the external heat source in inches or cm. X and Y coordinates are specified from the upper left corner of your underground raceway system.

Outside Diameter Outside diameter specifies the diameter of the external heat source in inches or cm. The thermal energy produced by the external heat source uses a constant temperature for the entire external heat source. The larger the diameter, the greater the thermal energy provided by the external heat source. The outside diameter is specified in inches or in centimeters.

Operating Temp. Operating Temp. specifies the surface operating temperature of the external heat source in degrees Celsius. The temperature is constant throughout the external heat source.

Underground Raceway Systems Calculation Methods


27.9 Calculation Methods PowerStation provides five types of cable derating calculations, namely, steady-state temperature calculation, uniform-ampacity ampacity calculation, uniform-temperature ampacity calculation, cable sizing, and transient temperature calculation. In the calculations, all conductors from the same cable branch are presumed to equally share the total line current. They can be located in the same conduit/location or different conduits/locations in the same raceway. Note that the cables located in different conduits/locations in general will not have the same temperature, even though they carry the same load current. However, if they are located in the same conduit/location, the calculated temperature will be the same. The raceway system can contain several raceways and external heat sources. The calculation considers the mutual heat effect of cables in the same raceway as well as in different raceways. It also considers the heat effect from external heat sources.

Cables with De-Energized Conductors For a DC or a single-phase cable branch, it is possible that some of the cable conductors may not carry current. For example, consider that a single-phase branch needs five conductors per phase to carry its load. Since a single-phase circuit has a forward and a return path, it requires ten conductors in total. If for some reason three-conductor cables are used for this branch, four, three-conductor cables will be needed, which equals a total of twelve conductors. This leaves two of the twelve conductors as non-current-carrying (de-energized) conductors. PowerStation will spread non-current-carrying conductors among individual cables for the branch. In this case, two of the four cables will have only two conductors carrying current. In the Cable Temperature section of the output report, PowerStation reports the number of energized conductors for each individual cable.

Voltage Used for Calculating Cable Dielectric Losses Since the cable dielectric losses are directly related to the voltage applied on the insulation layer, the cable operating voltage should be used for this calculation. In PowerStation, if a cable is a branch cable or an equipment cable, the nominal kV of the cable terminal bus will be used. For an underground cable (no terminal bus), the cable rated voltage is used. In the report, the voltage applied on the insulation layer is printed under the “Insulation Layer kV” column.

27.9.1 Steady-State Temperature Calculation The Steady-State Cable Temperature calculation determines the temperature of all the cable conductors involved in the raceway system under a specified loading condition. The calculation is based on the NEC accepted Neher-McGrath approach, which employs a thermal circuit model to represent heat flow situations. It is assumed that the cables have been carrying the specified load long enough that the heat flow has reached its steady-state and no more changes of temperature will occur throughout the raceway system. The cable temperature calculated is dependent on raceway system configuration, cable loading, and the location of each particular cable.



Maximum Number of Iterations The maximum number of iterations for the steady-state and transient temperature calculations is set to 50. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. Note that you must close PowerStation and launch it again to see the results of the changes made in the ETAPS.INI file. MaxIterForTempCalc=50

27.9.2 Cable Ampacity Calculation The Cable Ampacity calculation determines the maximum allowable load current that the cables in a raceway system can carry under the specified system conditions and the cable conductor temperature limit. PowerStation provides two approaches to ampacity calculation: Uniform-Ampacity calculation and Uniform-Temperature calculation. Both approaches employ the NEC accepted Neher-McGrath method to calculate cable temperature, but they differ in the criteria used to determine the maximum allowable load current.

27.9.3 Uniform-Ampacity (UA) Ampacity Calculation This approach is based on the equal loading criterion for ampacity calculation. It determines the maximum allowable load currents when all the cables in the system are equally loaded to the same percentage of their base loading. The base load is obtained from the Cable Library for the appropriate system configuration type, such as duct bank or directly buried raceways. The calculation involves an iterative process of cable temperature calculation and load adjusting, as listed below. 1. Determine an initial loading level based on the base ampacity from the Cable Library and using cable

derating factors for the given configuration. 2. Calculate cable temperature as in the steady-state temperature calculation described above. 3. Check cable temperature values against the cable temperature limit. 4. If the temperature of the hottest cable is within close range of the temperature limit, the solution has

been reached. If not, adjust the cable loading uniformly at the same percentage, either increasing or decreasing the loading in order to make the highest cable temperature come closer to the temperature limit. Then go to back to step 2 to recalculate cable temperature.

If the Update Currents from Ampacity Calc option is checked in the study case, the cable allowable current is updated by the calculated ampacity.

Maximum Number of Iterations The maximum number of iterations for uniform-ampacity and uniform-temperature calculations is set to 200. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. Note that you must close PowerStation and launch it again to see the results of the changes made in the ETAPS.INI file. MaxIterForAmpCalc=200



Cables with Fixed Current If the Fixed Current box in the Leading page of the Cable Editor is checked for a cable, the load current for this cable will be held constant in the ampacity calculation. The cable current used in the calculation depends on the Initial/Steady-State Amp selection in the study case.

27.9.4 Uniform-Temperature (UT) Ampacity Calculation This approach is based on the equal temperature criterion for ampacity calculation. It determines the maximum allowable load currents when all the cables in the system have their temperature within a small range of the temperature limit. Since all the conductors in a cable branch are assumed to equally share the load current, in the case where these conductors are not located in the same conduit/location, they may not have the same temperature. When this situation occurs, the temperature of the hottest conductor in this cable branch will be used to represent this cable branch. The calculation involves an iterative process, which adjusts cable loading current in each iteration so that the cable temperature approaches the temperature limit. The load adjustment in each step is determined based on the gradient of cable temperature change and therefore offers fast convergence to the solution. The following steps are involved in the calculation: 1. Determine an initial loading level based on the base ampacity from the Cable Library and using cable

derating factors for the given configuration. 2. Calculate cable temperature as in the steady-state temperature calculation described above. 3. Check cable temperature values against the cable temperature limit. If the temperature values of all

the cables are within close range of temperature limit, the solution has been reached. If not, determine the load change required for the cable temperature to approach the temperature limit based on the gradient of cable temperature change.

4. Update cable loading and go back to step 2 to recalculate cable temperature. If the Update Currents from the Ampacity Calculation option is checked in the study case, the cable allowable current will be updated by the calculated ampacity. Maximum Number of Iterations The maximum number of iterations for uniform-ampacity and uniform-temperature calculations is set to 200. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. MaxIterForAmpCalc=200

Acceleration Factor The uniform-temperature ampacity acceleration factor has a range between 0.0 and 2.0. The value can be set higher than the default setting of 0.7 to speed up the calculation; however, the calculation may diverge. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading.

UTAmpAccelFactor=0.7 Note that you must close PowerStation and launch it again to see the results of the changes made in the ETAPS.INI file.



Cables with Fixed Current If the Fixed Current box in the Leading page of the Cable Editor is checked for a cable, the load current for this cable will be held constant in the ampacity calculation. The cable current used in the calculation depends on the Initial/Steady-State Amp selection in the study case.

27.9.5 Cable Sizing The Cable Sizing calculation determines the minimum size for each cable that will carry the specified load current without violating the cable temperature limit. The cables considered as candidates for cable sizing are the ones that are flagged as available cables in the Cable Library of the same cable type, that is, they have the same voltage, insulation, conductor type, etc., as the cable to be sized. The calculation is an iterative process involving repetitively adjusting the cable size and calculating cable temperature. The cable temperature calculation is done in the same way as the steady-state temperature calculation described above. If there are no available alternative sizes for a cable, the cable will be considered not changeable. If a solution is reached, calculation results will be reported in the output report and the cables involved in the study will be changed to the new sizes if the Update Size option is checked in the study case.

Maximum Number of Iterations The maximum number of iterations for cable sizing calculations is set to 1000. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. Note that you must close PowerStation and launch it again to see the results of the changes made in the ETAPS.INI file. MaxIterForCableSizeCalc=1000

Cables with Fixed Size If the Fixed Size box in the Loading page of the Cable Editor is checked for a cable, the size of this cable will not be changed in the Cable Sizing studies.

27.9.6 Transient Temperature Calculation The transient temperature calculation yields cable temperature variations as a function of time in accordance to load changes. While the steady-state temperature calculation can be used to check the cable temperature under constant loading, the transient temperature calculation provides a tool to verify operation conditions of the raceway systems against the cable short-time or emergency temperature limits. In most cases, the short-time maximum allowable temperature of a cable is considerably higher than its steady-state temperature limit. For loads that have high peak values for only a short period of time, the transient temperature calculation can be used to determine the cable peak temperature and its duration, and to compare against its short-time maximum allowable temperature, resulting in a more economical design of your raceway systems.



The transient temperature calculation is based on a dynamic thermal model of the raceway system, constructed mainly from thermal resistance, thermal capacitance, and heat sources. The thermal resistance is used to represent different thermal layers from the cable conductor to ambient soil. The thermal capacitance is used to represent the capability of each layer to absorb the heat. When you change the cable loading, the heat generated by the loss in the conductor will change accordingly, resulting in a variation of the heat flow dissipated from the cable conductor to the ambient soil. As a result, the cable conductor temperature will vary to follow the load change pattern, at a rate of temperature change that depends on the resistance and capacitance values of the circuit. The cable load variations are defined in the Load Profile of the Cable Editor. The initial state of the raceway system is based on the initial load specified in the Cable Derating Study Case, either the load profile (the first current value in the profile list) or the operating load. It is assumed that all cables initially carry the initial load and have reached the steady-state.

Maximum Number of Iterations The maximum number of iterations for the steady-state and transient temperature calculations is set to 50. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. MaxIterForTempCalc=50

Maximum Transient Steps Maximum number of transient steps is set to 5000. To modify this value, enter the following command line in the ETAPS.INI file under the [ETAP PowerStation] heading. Note that you must close PowerStation and launch it again to see the results of the changes made in the ETAPS.INI file. MaxTransientStep=5000

Underground Raceway Systems Required Data


27.10 Required Data

27.10.1 Underground Raceway System Data The data for the underground raceway system can be entered from the Underground System Editor. The minimum requirement for underground system data includes soil type, soil thermal resistivity, and ambient temperature.

27.10.2 Raceway Data Two types of raceways are supported in the current version of PowerStation: Duct Bank Raceway and Direct Buried Raceway. Raceway data can be entered from the Raceway page of the Raceway Editor. The minimum requirement for raceway data includes raceway dimension, raceway fill type, and its thermal resistivity. You can run studies with raceways that contain no cables. However, you cannot run studies if the raceway contains unassigned cables (cables that are assigned to a raceway but are not located in a specific conduit or location).

Conduit/Location Data The data for conduit/location can be entered into the Location page of the Raceway Editor. A conduit/location can be empty (contain no cables).

Conduit A conduit can only be placed in a duct bank raceway. The minimum requirements for conduit data include location, type, outside diameter, and thickness.

Location A location is a specified space in a direct buried raceway in which cables are placed. Location can only be assigned to a direct buried raceway. The only requirement for location data is its location.

Cable Data Cable data is entered into several pages of the Cable Editor.

Data from the Info Page The cable type data must be available before performing any cable derating calculation. You can select cable type from the Cable Library by clicking on the Library button. Other data that is needed for cable derating calculations and can be entered into the Info page including the cable size and the number of conductors per phase. Special attention should be given to the Link to Library box. When this box is checked, the cable derating calculation will extract the cable physical data directly from the Cable Library; otherwise it will use the data from the Physical page of the Cable Editor.

Underground Raceway Systems Required Data


Physical Page This page is designed especially for entering parameters employed in cable derating calculations. The parameters describing the physical aspect of a cable are required to calculate cable electrical resistance, thermal resistance of different layers, dielectric losses, etc.

Loading Page The data entered in this page describe the loading condition of a cable. The Transient Load Profile data is used for transient temperature calculation. The Operating Load or the first current value in the Transient Load Profile list are used, depending on the selection in the Cable Derating Study Case, as the initial or steady-state load current in the transient temperature calculation, steady-state temperature calculation, and cable sizing. The Load Factor is used in all types of cable derating calculations to represent cyclic load conditions. The Projection Multiplication Factor is used to modify cable loading in the transient temperature calculation, steady-state temperature calculation, and cable sizing, if the corresponding option is checked in the Cable Derating Study Case. The Sheath/Armor Current is specified as a percentage of the load current. It represents the situation where the sheath/armor is intentionally utilized to carry part of the load current. In all other situations, sheath/armor current should be set to zero.

Ampacity Page The Application Multiplication Factor is used to modify cable loading in the transient temperature calculation, steady-state temperature calculation, and cable sizing, if the corresponding option is checked in the Cable Derating Study Case.

External Heat Source Data The external heat source data required for cable derating calculations include the location of the external heat source, its outside diameter, and its temperature.

Study Case Prior to performing any type of cable derating calculations, a Cable Derating Study Case must be selected. The study case contains information necessary to carry out the calculation.

Underground Raceway Systems Output Reports


27.11 Output Reports A text report is generated after performing a cable derating calculation. Printed on the top of each page of the output report is the general information about the project, the study cases, and the version of PowerStation, etc. The first page of the report contains information about the underground raceway system, including the number of raceways and external heat sources in the system. If there are external heat sources in the underground system, this information is printed on the second page. It is followed by raceway and cable information. Input data and calculation results for raceways and cables are grouped together according to raceways, namely, the conduits/locations and cable information, as well as the related calculation. Results will be printed together with the information of the raceway in which the conduits/locations and cables are located. This section of the output report is formatted according to the type of calculation being performed.

Steady-State Temperature Calculation This section of the output report starts with raceway information, followed by conduit/location information. It then presents information for cables, including cable parameters, calculated cable insulation thermal resistance, dielectric losses, etc. As the cable conductor temperature is the main result from the steady-state temperature calculation, these values are presented in the final portion of this section. Note that conductors that belong to the same cable and are located in the same conduit/location have the same temperature; therefore, the temperature for only one conductor is printed. CABLE AMPACITY DERATING ======================= Project: Example PowerStation 4.0.0C Page: 1 Location: Lake Forest, California Date: 10-12-2000 Contract: OTI-12345678 SN: 85OTI30125 Engineer: Operation Technology, Inc. Study Case: CD File: EXAMPLE _________________________________________________________________________________________________________________________________ This info is printed on top of every output report, 1st remark line. (120 characters) ================================================================================================================================= ETAP PowerStation _________________ Cable Derating Analysis _______________________ Cable Steady State Temperature Calculation UGS System Number of EHS Number of Raceway ____________ _____________ _________________ UGS1 1 1 Ambient Conductor Soil Earth Temp (°C) Temp (°C) Type RHO _________ _________ _____________ ______ 35.00 90.00 Clay Wet 90.00 Multiplication Factor: Global Projection MF = 100 % Initial/Steady State Amp: Operating Load Output File: C:\ETAPS30\PowerStn\Example\TranTemp.cdr



External Heat Source Information ________________________________ Horiz. Vertical Distance Distance OD Temp. No. ID (in) (in) (in) (°C) ___ ____________ ________ ________ _____ ______ 1 Steam Pipe 75.40 35.90 6.00 80.00 Raceway Information ___________________ Horiz. Vertical Fill Number Number Raceway Distance Distance Height Width ______________________ of of ID (in) (in) (in) (in) Type RHO Conduit Cable ____________ ________ ________ ______ ______ _____________ ______ _______ ______ RW1 19.20 30.00 20.40 43.50 Light Aggreg. 90.00 9 8 Conduit/Location Information ____________________________ Horiz. Vertical Duct Distance Distance Size Thick Fill No. ID (in) (in) Type (in) (in) (%) ___ ____________ ________ ________ _____________ _____ _____ _____ 1 Cond1 6.55 6.55 PVC__40 5.56 0.258 30.04 2 Cond2 14.05 6.55 PVC__40 5.56 0.258 18.49 3 Cond3 29.05 14.15 PVC__40 5.56 0.258 20.32 4 Cond4 6.55 14.05 PVC__40 5.56 0.258 13.36 5 Cond5 14.00 14.00 PVC__40 6.62 0.280 23.03 6 Cond6 21.50 14.00 PVC__40 6.62 0.280 12.66 7 Cond7 29.00 6.50 PVC__40 2.87 0.203 28.37 8 Cond8 21.50 6.50 PVC__40 2.87 0.203 28.37 9 Cond9 36.50 6.50 PVC__40 2.87 0.203 28.37 Cable Information _________________ No. Cab Insul Sheath of per Volt Cable Load Cond Insul Thick Shield Sheath Thick No. ID Size Cond Phs kV I Factor Type Type (mil) Status Type (mil) ___ ____________ ____ ____ ___ ____ ______ ______ _____ ________ _____ ______ ______ ______ 1 Cable8 500 1 1 15 234.00 100.00 CU RUBBER 2 295.0 Y None 0.00 2 Cable6 3/0 1 1 15 156.00 100.00 CU RUBBER 2 295.0 Y None 0.00 3 Cable2 4/0 3 1 5 203.09 100.00 CU RUBBER 190.0 Y None 0.00 4 Cable5 4/0 1 1 5 78.00 100.00 CU RUBBER 2 190.0 Y None 0.00 5 Cable1 4/0 1 1 15 94.00 100.00 AL RUBBER 2 295.0 Y None 0.00 6 Cable3 2 1 1 15 47.00 100.00 CU RUBBER 2 295.0 Y None 0.00 7 Cable4 350 1 1 5 60.66 100.00 CU RUBBER 2 190.0 Y None 0.00 8 Cable9 4/0 1 1 15 102.00 100.00 CU RUBBER 2 295.0 Y None 0.00 Jacket Cable Insul Insul Dielec Cable Cond Jacket Thick O.D. DC Res. Ther.R Layer Losses Temp Losses No. ID Type (mil) (in) (uOhm/ft) (Ohm/ft) kV (W/ft) Yc Ys (°C) (W/ft) ___ ____________ ______ ______ _____ _________ ________ _____ ______ ______ ______ ______ ______ 1 Cable8 None 0.00 1.60 21.63 1.735 8.66 0.107 0.018 0.000 79.37 4.37 2 Cable6 None 0.00 1.25 64.23 2.585 8.66 0.072 0.002 0.000 90.71 5.89 * 3 Cable2 None 0.00 2.28 50.98 0.603 2.40 0.008 0.007 0.021 101.65 8.22 * 4 Cable5 None 0.00 1.07 50.98 1.724 2.89 0.012 0.003 0.000 72.65 1.10 5 Cable1 None 0.00 1.31 83.50 2.385 8.66 0.078 0.001 0.000 82.55 2.72 6 Cable3 None 0.00 1.05 162.67 3.514 8.66 0.053 0.000 0.000 81.93 1.31 7 Cable4 None 0.00 1.25 30.77 1.410 2.89 0.015 0.008 0.000 76.93 0.41 8 Cable9 None 0.00 1.31 50.98 2.385 8.66 0.078 0.003 0.000 77.87 1.92 Cable Temperature _________________ Conduit No. of No. of Cable Cable Location Conductors Engergized Temp No. ID ID per Cable Cond/Cable (°C) ___ ____________________ ____________ __________ __________ ______ 1 Cable8-1A Cond1 1 1 79.37 2 Cable8-1B Cond1 1 1 79.37 3 Cable8-1C Cond1 1 1 79.37 4 Cable6-1A Cond2 1 1 90.71 * 5 Cable6-1B Cond2 1 1 90.71 * 6 Cable6-1C Cond2 1 1 90.71 * 7 Cable2 Cond3 3 3 101.65 * 8 Cable5-1C Cond4 1 1 72.65 9 Cable5-1B Cond4 1 1 72.65 10 Cable5-1A Cond4 1 1 72.65 11 Cable1-1A Cond5 1 1 82.55 12 Cable1-1B Cond5 1 1 82.55 13 Cable1-1C Cond5 1 1 82.55 *Indicates cables with conductor temperature exceeding its limit.



Ampacity Calculation The ampacity calculation results are reported in the same format as the steady-state temperature calculation, the only difference being that the cable current value reported is the cable maximum allowable load instead of the actual cable load current.

Cable Sizing Calculation The cable sizing calculation results are reported in the same format as the steady-state temperature calculation, the only difference being that the cable size reported is the smallest cable size that can carry the specified load current without violating the cable temperature limit.

Transient Temperature Calculation The results of the transient temperature calculation are represented in both text and plot formats. The text report has the same format as the report generated by the steady-state temperature calculation. As the cable temperature varies with time, the temperature values reported in the text report is the highest temperature value during the simulation period. The temperature plots can be viewed by clicking on the View Cable Temperature Plots button on the Cable Derating Toolbar. The Printing and Plotting Chapter describes features that will be helpful in viewing the plot.

Underground Raceway Systems Plots


27.12 Plots Click on the Plot icon to open the Cable Selection dialog box, which contains all the cables in the raceway system. Clicking on a cable will select the cable for plotting its temperature. If a cable is already selected, clicking on it again will deselect that cable. Clicking the OK button will open the Plot View, which will display the transient temperature for the selected cables. The Cable Selection dialog box displays the cable ID along with the conduit/location ID in which the cables are located and the raceway ID. Note that you can have more than one raceway in a U/G system, and the same cable can be placed in more than one raceway.

Temperatures for up to sixteen cables can be displayed in one plot. If more than sixteen cables are selected, the temperature for the first sixteen cables will be displayed in the plot. The Cable Transient Temperature plot indicates temperatures of selected cables as functions of time. You can change the size and font of the text (labels) by double-clicking on the labels. You can also change the type and color of plots (curves) by double-clicking on them. For more details, refer to Printing and Plotting.

Plots, which are generated as a result of transient temperature calculations, can be printed by any printer supported by your Windows platform. To print a plot, display the plot view, make formatting modifications, if required, and select the Print command from the File menu. You may have several plot views displayed on your screen; however, only one plot can be active at any time. The printed plot size is currently set to the size of the paper on which it is being printed.

Modifying Plot Parameters Plot parameters such as plot line type, axis, legend, and text can be modified directly from the plot view. For example, to modify plot line type, double-click on the plot line and change the line type from the Plot Parameter Editor. For more details see the chapter on Printing and Plotting.

Underground Raceway Systems Tutorial


27.13 Underground Systems Tutorial This tutorial provides a brief overview of the operation of the Underground Raceway System (UGS). Once you finish this tutorial, you will be familiar with some the key features and capabilities of the program and the various options available for performing cable derating analysis. Cable derating analysis is an important part of power system design and analysis. For designing a new system, it determines the proper size of cables to carry the specified loads. For analysis of an existing system, it examines cable temperatures and determines their ampacities.

Starting the PowerStation Program and Opening the Example Project

Start the ETAP PowerStation program by double-clicking on the icon. PowerStation organizes your work on a project basis. Each project provides all the necessary tools and support for modeling and analyzing an electrical power system. A project consists of an electrical system that requires a unique set of electrical components and interconnections. In PowerStation, each project provides a set of users, user access controls, and a separate database in which its elements and connectivity data are stored. Follow these simple steps to open the EXAMPLE project file.

Enter your User Name in the Logon Editor and select the Project Editor option in the Select Access Level Editor.



The Example project includes a one-line diagram of an electrical system. Notice the UGS1 view located behind the Study View. Click on the UGS1 view to bring it to the front and maximize it.

27.13.1 Cross Section Diagrams and Editors PowerStation provides a fully graphical Underground (U/G) Raceway System. Each PowerStation project supports a unique U/G raceway system with multiple views of the U/G system. Each view is conceptually a cross-section of the desired raceways and heat sources that are in the same vicinity.



Notice the toolbars on the top and the right-hand side of the U/G raceway cross-section view.



Editors Double-click on the raceway RW1 and view the Raceway Editor. This editor includes Raceway,

Location, and Cable information. Flip through the pages and familiarize yourself with the Raceway Editor. Note that the Help button is available on each page of all editors.

Click on OK and close the editor.

Double-click on the underground system and view Underground System Editor. This editor provides details regarding the overall layout of underground raceways, which includes global properties such as soil type and temperature.




Double-click on the External Heat Source. External heat sources can be placed in underground raceway systems to simulate steam pipes or other sources of heat in the vicinity of raceways.

27.13.2 Menu Bars and Toolbars

Power Station Menu Bar

The PowerStation Menu Bar contains a comprehensive collection of menu options. This menu bar is displayed when a UGS view is active. The PowerStation menu bar contains a list of menu options which, when an option is selected, activates a drop-down list of commands. Some of the menu options also activate an additional list of menus (an arrow pointing to the right denotes an additional menu). For example, select Project, Settings, and Data Type.

Project Toolbar

The Project Toolbar contains icons that allow you to perform shortcuts of many commonly used functions in PowerStation.



Mode Toolbar

Underground raceway system has two modes of operation, Edit, and U/G Cable Raceway.

Edit Mode Edit mode allows you to create a cross-section view of your underground raceway system.

Click on the Edit mode of the UGS Mode Toolbar.

To add elements to the UGS view you click on the elements on the Edit toolbar and add it to the UGS view.

Lets start by adding a New Duct Bank Raceway to the UGS View. Then add two New Conduits to the raceway.

Resize a conduit as follows:

• Click once on one of the conduits so it is selected. • Then move your cursor to one corner of the selection

box. A double-end arrow appears. • Left-click, hold, and drag the cursor. • Release the cursor when the desired conduit size is

reached. Note that you can also resize a conduit from its editor.





Next click on the New Cable icon on the Edit Toolbar and add a cable to the conduit. Then double-click on the cable cross-section and select a cable from the library.

• Select different cable sizes and notice how the cross-section size of the cable changes

accordingly. • Click on one conductor and notice the cable phase annotation. • Select a conductor and drag it to the second conduit.

Study Mode Cable Derating Study mode enables you to create and modify study cases, perform system analysis, and view output reports and plots.

Click on the U/G Cable Raceway icon on the Mode Toolbar to go to the Cable Derating Study Mode. Cable Derating Study Toolbar and Cable Derating Study Case Toolbar are available in the Study mode of operation.

Cable Derating Study Toolbar When a study mode is active (selected), the Study Toolbar for the selected study is displayed on the right side of the screen. By clicking on the buttons on the Study Toolbar, you can run studies, view output reports, view plots, and change display options. Cable Derating Study Case Toolbar and Editor When program is in Study mode, the Study Case toolbar appears on the top toolbar. This toolbar contains Cable Derating Study Case, output report name, and viewer.



Click on the Edit Study Case icon on the Study Case toolbar.

The Cable Derating Study Case Editor contains solution control variables, cable loading parameters, and options for output reports. PowerStation allows you to create and save unlimited numbers of study cases. Cable derating calculations are conducted and reported in accordance with the settings you have specified in the study case editor. Note that you can have an unlimited number of study cases and can easily switch between the 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.




27.13.3 Exercise Lets do an exercise to get the feel of how the program works. You have learned how to add elements to the UGS view earlier in this tutorial. In this exercise you can run a study and study the calculation results.

Steps 1. Go to the Project View and open UGS2 view. This is a working example and you can perform all

Cable Derating Analyses for learning purposes.

This example consists of one Raceway (RW2), six conduits, and six routed cables. There is a steam pipe in the close vicinity of this raceway. 2. Activate UGS2 view by clicking once on the view. Study toolbar appears on the right-hand side. 3. Run Steady-State Temperature analysis by clicking on its icon.



4. View the output report for the calculated results. 5. Perform other calculation methods and view the output report.



Cable Temperature _________________ Conduit Cable Cable Location Temp No. ID ID (°C) ___ ____________________ ____________ ______ 1 Cable10 Loc1 54.84 2 Cable2 Loc2 70.41 3 Cable4-1A Loc3 66.08 4 Cable1-1A Loc4 76.18 5 Cable8-1A Loc5 88.51 6 Cable3-1A Loc6 81.94

CalculatedResults

Temperature Warning

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