General EMF Workstation Questions
How do I determine which module of the EMFW should be used to
solve my EMF problem?
This is a good question and the answer depends on what sort of
output you want. However, you can use the following guidelines to help make a decision:
Use EXPOCALC if you need to calculate electric fields over a 2-D
area, or if you want to compute human exposure to EMF. But EXPOCALC will not compute EMF
for lines that converge or for multiple transmission line circuits in a right of way.
Use ENVIRO if you need a simple magnetic field, electric field or
audible noise lateral profile from a single span of transmission or distribution line. If
the lines you are modeling contain shield wires that are grounded at each tower then
ENVIRO is the only module that will compute the induced current on the shield wires.
Use either RESICALC or SUBCALC for most other EMF problems. They
are the most versatile and comprehensive modules on the EMFW. They only calculate magnetic
fields, but can model very complex arrays of conductors such as those found in substations
and distribution systems. They also produce presentation-quality graphics that can be
imported into word processors. They are the only modules that produce 3-D surface maps of
the magnetic fields. Use these modules if you need to compute a profile around the
perimeter of a building or property boundary. SUBCALC should be used if the problem
involves modeling substation equipment such as bus, transformers, cap banks or reactors.
RESICALC should be used if you want to model the effects of ground currents in residential
ground systems. Otherwise the two programs are identical and the choice is yours.
How can I compute induced currents on shield wires?
Although the programs currently do not have the ability of
calculating induced currents on shield wires (this feature is coming), you can use ENVIRO
to help out with this task. Do the following:
If your model consists of a simple transmission line right of way you
can compute the induced currents in the shield wires using ENVIRO.
Take the induced currents computed by ENVIRO and type them into the
load configurations for the towers.
Calculate the final magnetic fields.
You must rerun the induced current calculations in ENVIRO for each
loading condition that you wish to model.
How do I include the graphics generated by the programs into my
Do the following:
Once you have the desired graphic displayed on the screen, choose
Copy from the Edit menu.
Make sure the "Copy Graphic As Metafile" is selected in
the Clipboard Copy dialog box then click the OK button (this copies the graphic to the
Windows Clipboard in metafile format).
Choose Edit, Paste in your word processor. You may have to resize
the graphic in your word processor, but it should scale nicely.
Note: the Edit,
Paste feature does not work properly in any of the Microsoft Office 97 products.
How do I import the calculation results into other applications
such as a spreadsheet program or statistical package?
As long as the program importing the results supports reading
delimited ASCII files then do the following:
Choose ASCII Output from the Options menu.
Make sure the "Delimited" radio button is selected and
that the proper delimiter is selected (most programs recognize commas or spaces as
Next choose either Output, ASCII, Reference Grid or Output, ASCII,
Profile depending on what data you want to import into your spreadsheet.
From your spreadsheet program follow the instructions for
importing ASCII files. Microsoft Excel 5.0 and 7.0 provides a nice wizard for doing this.
Do the programs support drag and drop?
Yes, when opening new files. Try this for RESICALC (the same
technique also works for SUBCALC):
Start the RESICALC program.
Next, open File Manager.
Resize and arrange the two applications so you can see both
windows side by side.
From File Manager choose any RESICALC data file (.RDW extension)
and drag it over to the RESICALC window.
That file will now become the active model in RESICALC.
This is a great way to quickly view the contents of files without
having to go to the File Open dialog box each time. This process also works with the
Windows 95 Explorer.
Why do the programs take such a long time to redraw large models?
One reason is the amount of detail displayed with the model. You
should turn off the conductor indicators in RESICALC while you are modeling a very complex
situation that contains a large number of conductor segments. This will help speed up the
redrawing process that constantly occurs during the layout of a model. Once you have
completed the model, and you want to print a copy, turn them on. Remember to turn them off
again after printing. Also, if you have modeled Capacitor Banks in SUBCALC, then these
objects always take a long time to paint.
Can the programs model underground cables?
The current versions of RESICALC and SUBCALC have no specific
tools for modeling underground cables such as pipe-type cables and cables with concentric
neutrals. The existing tools are primarily designed to model overhead lines but have the
flexibility to model just about any line above or below the ground. You can use the
distribution line tool in RESICALC and the buswork tool in SUBCALC to simulate the
When modeling underground cables, you should keep in mind that
you will most likely get magnetic fields that are overestimated near the cables because
the program does not calculate induced currents on pipes and thus will not attenuate the
Is it important to model uneven terrain?
Just as with any scientific modeling, you should not take any
shortcuts when building your model when you can avoid it. Oversimplifying your model can
invalidate it. Certainly, those who will be scrutinizing your work will be looking for any
inconsistencies and could question it.
Probably the best way to avoid criticism is to validate your
model by having close correlation between measured and calculated magnetic fields. If
there are significant deviations, you will want to adjust the conductor heights to account
for uneven terrain.
How do you model Uneven Terrain?
Currently, the only way to model uneven terrain is to adjust the
conductor heights. To do this, we must first choose some location in our model as our
reference. This location will provide our base elevation from which we will make
adjustments to the conductor heights. We will not make any adjustments to the conductor
heights at or near the reference location. The conductor heights away from the reference
location will be offset by the difference in the terrain elevations from the base
Probably the easiest approach to this problem is to first ignore
the terrain elevations and lay out the model assuming a flat earth. We can then save this
model for future comparison once we have made the elevation adjustments. To make these
adjustments we will select each line in turn and edit the tower/pole locations. The Tower
and Pole Locations dialog boxes will not only let us change the location of a tower or
pole, it will also let us change the attachment and midspan heights of the lowest
The attachment and midspan heights of the conductors are relative
to ground zero, which is also the fixed elevation of each tower and pole. If our base
elevation is assumed to be ground zero, then we will need to add the difference of the
base elevation and the actual elevation of the tower or pole or at midspan to the
attachment and midspan heights of the lowest conductor. The program will then adjust the
heights of the other conductors relative to the height of the lowest conductor so that
there is no change to the conductor configuration.
To illustrate this, refer to
Figure 1 (6Kb .gif file). In this example, a
transmission line slopes down the ridge of a hill. The lines initial configuration
puts the attachment height of the lowest conductor at 55 feet and the midspan height at 45
feet. After laying out the line, the conductor heights are modified using the Tower
Locations dialog box. The attachment and midspan heights of the lowest conductor are
recalculated using Equation 1 and are
summarized in Table 1 and
It is not difficult to model uneven terrain even though the program
does not provide an explicit interface for defining the elevation of the terrain. Most of
us have found that when we specify the location of the towers and poles of transmission
and distribution lines the program only accepts the (x, y) coordinates. Thus, we do the
next best thing and adjust the attachments and midspan heights of the conductors to take
into account the terrain elevation.
Adjusting the heights of the conductors to model uneven terrain is
only part of the solution to accurate magnetic modeling. The other part involves adjusting
the height of the reference grid and profile definitions to take into account the terrain
elevation. The process for doing this is the same as described above for adjusting the
conductor heights. Simply offset the reference grid or profile height by the difference in
the base elevation and the terrain height. However, the reference grid can only be used to
calculate the magnetic field over a flat area.
Typically, the reference grid is best used to map the magnetic field
in a flat area such as within some building space. Thus, it will be ineffective over an
area of uneven terrain. In this case, it will be better to use the profile tool to map the
magnetic field. Typically, the profile is used to map the magnetic field around the
perimeter of some property or transverse some line. However, it can be used to map the
magnetic field over some area. In any case, the key point to remember is that the profile
will have multiple segments so that it can be modified to fit the terrain.
The number of segments in the profile will depend on the contour of
the terrain. Where the terrain changes significantly there will be more profile segments
than where it does not. The more segments used, the more accurate the profile will be
along the segment. The profile segments can be made to follow the terrain contour by
adjusting the height at the beginning and end of each profile segment. The height
adjustments are made in the Profile Definition dialog box and can be calculated using the
same technique (Equation 1) set forth for height adjustments to conductors.
It is not impossible to model the magnetic field over an area of
uneven terrain. It only requires a little resourcefulness and reformulation to overcome
this program limitation. Thus, using the techniques described above, it is even possible
to define a profile such that it serves as a reference grid for the magnetic field
calculations. Since the program has an option to output an ASCII file of the calculation
results, these can then be imported into other applications such as a spreadsheet program
to produce graphical output such as contour and surface plots.
How do I model buswork?
This depends on what exactly you are trying to model with the
buswork tool. In SUBCALC, the buswork tool is designed to help you model buswork where the
are parallel, i.e., maintain constant spacing
have a flat configuration, either horizontal or vertical
make 90 degree bends.
Simple buswork generally satisfies these criteria. In other
cases, the buswork tool can be used to model underground lines, as well as equipment such
as switchgear. When using it for more complicated modeling, it is best to:
determine the number of supports you need (adding extra supports
when not knowing exactly how many are needed)
lay out the buswork in some general way such as horizontally
across the screen
select the entire bus and use the Bus Support Locations dialog box
to relocate each bus support to their proper position and change their rotation to 90
degrees (to simplify visualization of the sub conductors in the Bus Support Configuration
using the Bus Support Configuration dialog box, adjust the
configuration of each bus support as needed to model the path of the conductors
One thing to watch out for when modeling buswork are conductors
that end up occupying the same space (i.e., they physically cross or coincide with each
other). SUBCALC will not warn you of this condition and it can significantly impact your
magnetic field calculations.