Processing simulation data from power flow analysis

The intro is a bit long. If you're not interested, then please read the update, and have a look at the specific parts I'm highlighting.

I'm very interested in any improvements, but you can assume that all calls starting with psspy. are correct and can't be changed. Also, the calls to psspy that are inside a loop have to be inside a loop, I can't call the functions with several input values.

The code is written in Python 2.7. This is because the simulation tool doesn't work with newer versions.

Update:

In case the code is too long for anyone to bother reviewing it, I'll write up some specific lines that probably could need some reviewing:

• The way I create branch_string. First: nodes_from_string = [str(x) for x in nodes_from], followed by branch_string = [nodes_from_string[x] +'-' +nodes_to_string[x] for x in range(0, len(nodes_from))].

• Is this a good way of doing this. I'm not using nodes_from_string later in the code, but I do nf = nodes_from[branch] and nf_str = str(nf) inside the loop.

• What about the part where the plots are created? Starting with fig = plt.figure().

• Should I do this outside the loop instead? If so, how could this be done in a simple manner?

• Can I simplify the way I'm creating datasheets and writing to Excel?

• Do I use enumerate as it should be used in the last 3 rows? Izero_3 is a np.array.

Explanation:

The code below calls a simulation software (called Power System Simulator for Engineering), and runs power flow analysis using the module psspy (PSS/E to Python).

The code works fine, but unfortunately you can't run it as it stands now, since the software is not a free program, and you don't have the power system model. I've provided sample input variables that can be used instead of the function calls (there are only a few lines that must be changed). This way, the bottom half of the code can be tested properly. I'll also provide an overview of the different outputs the simulation tool gives, and

There's only a single thing I can spot as a non-python programmer:

if ierr == 0:
    print "Case loaded: " + CASE

if ierr != 0:
    sys.exit("Case could not load. Check name and folder!")

You can use else here.

if ierr == 0:
    print "Case loaded: " + CASE
else:
    sys.exit("Case could not load. Check name and folder!")

StackExchange Code Review Q#136618, answer score: 3