There is an entire science to modelling distribution and transmission circuits, and "guessing" various loads/voltages/PFs so you know how to adjust, compensate and protect a certain section of line or a station. There is some nice software for it, and it's one of those things you wonder how it ever gone done before computers. Not that it would be impossible, but you cant be as "creative" when it takes you several hours to re-test each scenario. Doing things manually (transparent sheets laid over each other ect) didn't allow you to push equipment closer to tolerances, so I think you actually ended up with a better designed system however. (Ie. If the computer says within specs, even if it's within 0.5%, you probably do it, but if the dot is right on the line, most engineeers would say NO and rethink their setup)
You will probably take this as a flame / personal attack, it isn't.
I want to pull my hair out when I read stuff like you just wrote, you are making the classic mistake, assuming the computer software is "modelling" something with accuracy.
If it was Open Source software and anyone could see the code then I would have some sympathy with anyone claiming they knew what was going on.
If it is closed source / proprietary code then it doesn't matter how accurate it appears to me, you are using the Magic 8 ball to get answers, because you cannot manually check the calculations that the computer is doing.
This software by the way will be written by coders, not qualified and experienced electrical engineers.
So you run some numbers manually, it is slower, and you get DIFFERENT ANSWERS.
So you turn around and ignore this discrepancy as being hugely significant, declare the computer to be accurate and the manual system to be less precise, and away you go.
The truth is hidden in what you said, computers are fast, you can run ten or twenty scenarios in the time it takes to do one manually.
The calculation process thus loses it's importance, and your respect, and as soon as that happens you stop adhering to all the traditional rules, based on experience, that were there simply because calculation took a long time to do right, so you didn't mess with it.
But the real problem is unless you have a set of "workings" for each calculation, you're using a Magic 8 ball, but nobody is admitting that, everyone is claiming the computer calculations are god.
I knew someone who used to work on finite element modelling at a university with close links to the auto industry, which uses it to design and predict things like crumple zones, so he decides to compare real wrecked cars with the models, and found HUGE differences, and started to investigate... he doesn't work in finite element any more...
I use computers all day, but when I started using them everyone constantly drummed a phrase in to you, Garbage In, Garbage Out, so unless your transmission line modelling software can include calculations for the effects of humidity, rain, ice on the cables (capacitance etc) precise grades of cable metal, wooden vs steel tube vs steel frame towers, etc etc etc etc, you have no way of assessing how much garbage is going in.