Electrical Engineering & MS Excel 2

[cherryg]

As an electrical engineer, I have used numerous excel sheets for various purposes. The most common ones are:
a. Cable sizing-Ampacity
b. Cable sizing-Voltage drop & Short circuit
c. Heat Load Calculation
d. Load List
e. Lightning protection risk calculation
f. Cable Tray sizing
g. Cable Pull Calculation
h. pu calculation for short circuit
i. Motor starting time
j. Overhead sag-tension calcs
k. DC Battery sizing (IEEE485)
l. Battery Charger sizing

If you have used excel sheets for any of the above or other purposes, please share your thoughts.

 

[electricpete]

I've done quasi-static motor starting time calcs using excel.
T = J * dw/dt
t = integral {J / T((w))} dw

where w is radian speed and
where T((w)) would be motor torque speed curve minute pump torque speed curve.

If you tried to integrate until T(w) is 0, you face an interesting dilemma... the motor never gets there because acceleration approaches zero as w approaches the point where T((w)) = 0. You could create smaller and smaller step sizes and in theory I think accelerating time if you had perfect precision calculations would be infinite. So we can see the calculated time is very sensitive to the endpoint of the calculation.

Luckily, it is usually sufficient to cut off when the motor reaches full load speed rather than integrating until T(w) = 0

Comments - excel is a good tool for many calculations.

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(2B)+(2B)' ?

 

[magoo2]

I've done some calculations involved with induced voltages involving a transmission line and a distribution line based on capacitive coupling. It was a three-phase calculation with matrices.

I've done something similar with induced voltages on a light rail system from a nearby distribution line.

I've also set up worksheets to do fault calculations based on symmetrical components.

Pete's motor starting calcs sound interesting.

 

[cherryg]

Yes Electricprete..this is exactly the way I did the calcs...the laborious part is noting down the torque values for each speed value from 0 to near synchronous speed for both the motor and the load. The method has been lucidly explained in the attached link. Also, attention is required for the units (lb-ft to Nm). Also, the load torque may not be at the same speeds on the graph as the motor torques. Thus, interpolation is required to bring the torques to the same speed values.

 

[cherryg]

Some more calculations that I remember having done is:

a. the calculation of magnetic field at a certain coordinate, based on sections of DC Bus bars carrying 96kA of current in an Aluminum Smelter
b. Regression analysis to derive a two layer soil resistivity model using formula in Appendices of IEEE 80. This comes useful since ETAP grounding module can only use a two layer soil resistivity model.

One useful task that can be done using excel is to generate Data Sheets using a master table, and a macro, which serves to replace the certain characters. Important thing to remember is 95% of a Data sheet remains the same. The rest needs to be changed for a particular equipment.

Macros with suitably filled excel sheet can also be used to generate Microstation schematics! There is a bit labor in preparing the template schematics. But once it is done, schematic generation is a breeze.

 

[cherryg]

One good source for Electrical engineering spreadsheets is Professor C.S Indulkar's site as given below. One can always improvise on these sheets.