Extra features¶

roseau-load-flow comes with some extra features that can be useful for some users.

Graph theory¶

ElectricalNetwork.to_graph() can be used to get a networkx.Graph object from the electrical network.

The graph contains the geometries of the buses in the nodes data and the geometries and branch types in the edges data.

Note

This method requires networkx which is not installed by default in pip managed installs. You can install it with the "graph" extra if you are using pip: pip install "roseau-load-flow[graph]".

In addition, you can use the property ElectricalNetwork.buses_clusters to get a list of sets of IDs of buses in galvanically isolated sections of the network. In other terms, to get groups of buses connected by one or more lines or a switches, stopping at transformers. For example, for a network with a MV feeder, this property returns a list containing a set of MV buses IDs and all sets of LV subnetworks buses IDs. If you want to get the cluster of only one bus, you can use Bus.get_connected_buses

If we take the example network from the Getting Started page:

>>> set(source_bus.get_connected_buses())
{'sb', 'lb'}
>>> set(load_bus.get_connected_buses())
{'sb', 'lb'}
>>> en.buses_clusters
[{'sb', 'lb'}]

As there are no transformers between the two buses, they all belong to the same cluster.

Conversion to symmetrical components¶

roseau.load_flow.converters contains helpers to convert between phasor and symmetrical components. For example, to convert a phasor voltage to symmetrical components:

>>> import numpy as np
>>> from roseau.load_flow.converters import phasor_to_sym, sym_to_phasor
>>> v = 230 * np.exp([0, -2j * np.pi / 3, 2j * np.pi / 3])
>>> v
array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j])
>>> v_sym = phasor_to_sym(v)
>>> v_sym
array([[ 8.52651283e-14-1.42108547e-14j],
       [ 2.30000000e+02+4.19109192e-14j],
       [-7.10542736e-14-2.84217094e-14j]])

As you can see, for this positive-sequence balanced voltage, only the positive-sequence component is non-zero. Converting back to phasor, you get the original voltage values back:

>>> sym_to_phasor(v_sym)
array([[ 230.-7.21644966e-16j],
       [-115.-1.99185843e+02j],
       [-115.+1.99185843e+02j]])

You can also convert pandas Series to symmetrical components. If we take the example network of the Getting Started page:

>>> from roseau.load_flow.converters import series_phasor_to_sym
>>> series_phasor_to_sym(en.res_buses_voltages["voltage"])
bus_id  sequence
lb      zero        8.526513e-14-1.421085e-14j
        pos         2.219282e+02+4.167975e-14j
        neg        -5.684342e-14-2.842171e-14j
sb      zero        9.947598e-14-1.421085e-14j
        pos         2.309401e+02+3.483159e-14j
        neg        -4.263256e-14-2.842171e-14j
Name: voltage, dtype: complex128

Roseau Load Flow also provides useful helpers to create three-phase balanced quantities by only providing the magnitude of the quantities. For example, to create a three-phase balanced positive sequence voltage:

>>> import numpy as np
>>> import roseau.load_flow as rlf
>>> V = 230 * rlf.PositiveSequence
>>> V
array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j])
>>> np.abs(V)
array([230., 230., 230.])
>>> np.angle(V, deg=True)
array([   0., -120.,  120.])

Similarly, you can use rlf.NegativeSequence and rlf.ZeroSequence to create negative-sequence and zero-sequence quantities respectively.

Potentials to voltages conversion¶

roseau.load_flow.converters also contains helpers to convert a vector of potentials to a vector of voltages. Example:

>>> import numpy as np
>>> from roseau.load_flow.converters import calculate_voltages, calculate_voltage_phases
>>> potentials = 230 * np.array([1, np.exp(-2j * np.pi / 3), np.exp(2j * np.pi / 3), 0])
>>> potentials
array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j,
          0.  +0.j        ])
>>> phases = "abcn"
>>> calculate_voltages(potentials, phases)
array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j]) <Unit('volt')>

Because the phases include the neutral, the voltages calculated are phase-to-neutral voltages. You can also calculate phase-to-phase voltages by omitting the neutral:

>>> calculate_voltages(potentials[:-1], phases[:-1])
array([ 345.+199.18584287j,    0.-398.37168574j, -345.+199.18584287j]) <Unit('volt')>

To get the phases of the voltage, you can use calculate_voltage_phases:

>>> calculate_voltage_phases(phases)
['an', 'bn', 'cn']

Of course these functions work with arbitrary phases:

>>> calculate_voltages(potentials[:2], phases[:2])
array([345.+199.18584287j]) <Unit('volt')>
>>> calculate_voltage_phases(phases[:2])
['ab']
>>> calculate_voltage_phases("abc")
['ab', 'bc', 'ca']
>>> calculate_voltage_phases("bc")
['bc']
>>> calculate_voltage_phases("bcn")
['bn', 'cn']

Constants¶

roseau.load_flow.utils.constants contains some common constants like the resistivity and permeability of common conductor types in addition to other useful constants. Please refer to the module documentation for more details.

An enumeration of available conductor types can be found in the roseau.load_flow.utils.types module.

Voltage unbalance¶

It is possible to calculate the voltage unbalance due to asymmetric operation. There are many definitions of voltage unbalance (see [GMR19]). In roseau-load-flow, you can use the res_voltage_unbalance() method on a 3-phase bus to get the Voltage Unbalance Factor (VUF) as per the IEC definition:

\[VUF = \frac{|V_{\mathrm{n}}|}{|V_{\mathrm{p}}|} \times 100 (\%)\]

Where \(V_{\mathrm{n}}\) is the negative-sequence voltage and \(V_{\mathrm{p}}\) is the positive-sequence voltage.

Note

Other definitions of voltage unbalance could be added in the future. If you need a specific definition, please open an issue on the GitHub repository.

Bibliography¶

[GMR19]

Kshitij Girigoudar, Daniel K. Molzahn, and Line A. Roald. On the relationships among different voltage unbalance definitions. In 2019 North American Power Symposium (NAPS), volume, 1–6. 2019. doi:10.1109/NAPS46351.2019.9000231.