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Frequently Asked Questions

By EMFW Programmers



Questions

The following questions are answered in this article:

 


 

Questions and Answers

Q:

How do I determine which module of the EMFW should be used to solve my EMF problem?

A:

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:

  1. 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.
  2. 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.
  3. 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.

 


 
NOTE: The following RESICALC tips will also work in SUBCALC.  

Q:

How can I compute induced currents on shield wires in RESICALC?

A:

Although RESICALC currently does not have the ability of calculating induced currents on shield wires (this feature is coming), but you can use ENVIRO to help out with this task. Do the following:

  1. If your model consists of a simple transmission line right of way you can compute the induced currents in the shield wires using ENVIRO.
  2. Take the induced currents computed by ENVIRO and type them into the load configurations for the towers in RESICALC.
  3. Calculate the final magnetic fields in RESICALC.
  4. You must rerun the induced current calculations in ENVIRO for each loading condition that you wish to model in RESICALC.

 


 

Q:

How do I include the graphics generated by RESICALC into my word processor?

A:

Do the following:

  1. Once you have the desired graphic displayed on the screen, choose Copy from the Edit menu in RESICALC.
  2. 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).
  3. Choose Edit, Paste in your word processor. You may have to resize the graphic in your word processor, but it should scale nicely.

 


 

Q:

How do I import the calculation results into other applications such as a spreadsheet program or statistical package?

A:

As long as the program importing the results supports reading delimited ASCII files then do the following:

  1. Choose ASCII Output from the Options menu.
  2. Make sure the "Delimited" radio button is selected and that the proper delimiter is selected (most programs recognize commas or spaces as delimiters).
  3. Next choose either Output, ASCII, Reference Grid or Output, ASCII, Profile depending on what data you want to import into your spreadsheet.
  4. 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.

 


 

Q:

How do I model buswork?

A:

This depends on what exactly you are trying to model with the buswork tool. The buswork tool is designed to help you model buswork where the conductors:

  1. are parallel, i.e., maintain constant spacing
  2. have a flat configuration, either horizontal or vertical
  3. 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:

  1. determine the number of supports you need (adding extra supports when not knowing exactly how many are needed)
  2. lay out the buswork in some general way such as horizontally across the screen
  3. 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 dialog box)
  4. 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.

 


 

Q:

Is it important to model uneven terrain in RESICALC and SUBCALC?

A:

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.

 


 

Q:

Do RESICALC and SUBCALC support drag and drop?

A:

Yes, they do for opening new files. Try this:

  1. Start the SUBCALC program.
  2. Next, open File Manager.
  3. Resize and arrange the two applications so you can see both windows side by side.
  4. From File Manager choose any SUBCALC data file (.SDW extension) and drag it over to the SUBCALC window.
  5. That file will now become the active model in SUBCALC.

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.

 


 

Q:

Why do RESICALC and SUBCALC take such a long time to redraw large models?

A:

One reason is the amount of detail displayed with the model. You should turn off the conductor indicators in RESICALC and SUBCALC 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.

 


 

Q:

Can RESICALC or SUBCALC model underground cables?

A:

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.

When modeling underground cables, you should keep in mind that you will most likely get magnetic fields that are over estimated near the cables because the program does not calculate induced currents on pipes and thus will not attenuate the fields.

 

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