The central class of the krangpower package is the eponymous Krang. It is designed to provide easy and intuitive interaction. Let’s see the basics of Krang usage with a small walkthrough.

>>> import krangpower as kp
>>> um = kp.UM
>>> src = kp.Vsource(basekv=15000*um.V)
>>> myKrang = kp.Krang('mighty_krang', src)
  • @2 Krangpower uses the physical quantity management package pint, so the first thing we did here is to bring in the local namespace krangpower’s UnitRegistry: the constant UM. Think of it as an object whose attributes are the measurement units.
  • @3 Every circuit has to be initialized with a slack voltage source, so Krang will need one. In krangpower, voltage sources are represented by Vsource. You can initialize Vsource, or any other electrical entity, with a set of keyword arguments to override the default values. We will call them “parameters”. Here we edited just the parameter ‘basekv’ to a value of 15000 Volts. More on parameters later.
  • @4 Here we instantiate a Krang with a name string and our Vsource. Both parameters are optional; if not provided, they will default to 'Unnamed_Krang' and kp.Vsource(). We can now start to add stuff to myKrang.
>>> lc = kp.LineCode_S('lcs1', r0=1*um.ohm/
>>> myKrang << lc
>>> myKrang['sourcebus', 'alpha']
<BusView('sourcebus', 'alpha')>
>>> myKrang['sourcebus', 'alpha'] << kp.Line(length=45*um.ft).aka('line1') * lc
>>> myKrang['line1']
<PackedOpendssElement: line1>
>>> myKrang['line1']['r0']
<Quantity(0.001, 'ohm / meter')>

More irons in the fire.

  • @5 We instantiate a LineCode_S. The syntax is the same as the Vsource, except that we must specify a name as first parameter. Because they’re not made of iron & copper but of information, LineCodes have a name of their own and do not have to be aliased every time they’re used (see line 9).
  • @6 Linecodes are meant to be associated to Lines. To make use of lc, we first have to inform myKrang of its existence. A Linecode is not bound to a bus or couple of buses; so we add it directly. In krangpower, the operator that adds a component to a Krang is left shift, <<.


Since version 0.2.1, it’s optional to explicitly declare abstract entities before declaring objects to which they are associated. Krangpower automatically declares associated entities that were not previously declared.

  • @7 This line demonstrates bracket indexing Krang with a tuple. The object returned is a BusView. You can add object that require topological collocation to BusView, in the same way of Krang themselves.

  • @9 This line has a lot going on.
    • We are instantiating a Line specifying its length in feet - we can use any length unit, krangpower will take care of the conversion. In order to be added to the circuit, the line has to be aliased with the method aka; in this way, it will have a name inside the circuit.
    • The line is then associated with lc, so it will make use of it in defining its impedance; the association operator is multiplication, *.
    • The line is added to the BusView we saw at point 7.

    Note: The default name of the output bus of the circuit’s slack Vsource is ‘sourcebus’. You can customize it by passing it as a third parameter to Krang constructor.

  • @10 Now that ‘line1’ is inserted into myKrang, we can retrieve it by bracket indexing Krang with a string with its name. The object retrieved is a PackedOpendssElement.

  • @12 Suffice to say, for now, that we can retrieve a PackedOpendssElement’s parameters with bracket indexing; here we print its r0. As expected, it’s a pint Quantity, and it’s coincident with lc

>>> myKrang['alpha']
<PackedOpendssElement: alpha>
>>> myKrang['alpha',]
>>> myKrang['alpha',] << kp.load(kv=15*um.kV, kW=130*um.kW)
  • @14,@16 Demonstrate again, in the tricky case of buses, bracket indicization with strings and tuples. In the first case, as expected, we get the bus ‘alpha’ as a PackedOpendssElement; in the second case, we get a BusView of the single bus ‘alpha’.
  • @18 We can add components bound to a single bus to the BusView; in this case, for example, we add a Load, instantiated with the usual keyword arguments passed to the constructor.