Ground

Definition

The ground element represents an earth connection where the earth is represented as an ideal conductor. A ground can be used to connect several elements. A ground is mandatory in a line model with shunt elements. The symbol of a ground element is:

A diagram of a ground element

This element adds the equation \(\underline{I_{\mathrm{g}}} = 0\), where \(\underline{I_{\mathrm{g}}}\) is the sum of the currents of all elements connected to the ground.

Warning

In electrical engineering, it is common to also add the equation \(\underline{V_{\mathrm{g}}}=0\) when defining a ground element. If you want to do so, you must add a PotentialRef element as defined in Potential Reference.

Usage

In Roseau Load Flow, several grounds can be defined leading to ground elements with a non-zero potential. Here is an example with two ground elements g1 and g2.

After solving this load flow, the following assertions will be verified:

  • The potential of the ground g1 will be 0V as defined by the potential reference pref.

  • There is no reason for the potential of g2 to be zero too.

  • The sum of currents flowing through the shunt admittances of the second line will be zero as they are all connected to the ground g2 and no other elements are connected to this ground.

  • The sum of currents flowing through the shunt admittances of the first line will be equal to the sum of the currents of the elements connected to phase “a” of the first bus.

import functools as ft
import numpy as np
import roseau.load_flow as rlf

# Define two grounds elements
g1 = rlf.Ground(id="g1")
g2 = rlf.Ground(id="g2")

# Define three buses
bus1 = rlf.Bus(id="bus1", phases="abc")
bus2 = rlf.Bus(id="bus2", phases="abc")
bus3 = rlf.Bus(id="bus3", phases="abc")

# Define a voltage source on the first bus
un = 400
vs = rlf.VoltageSource(id="source", bus=bus1, voltages=rlf.Q_(un, "V"))

# Define the impedance and admittance parameters of the lines (can be reused)
parameters = rlf.LineParameters(
    id="parameters",
    z_line=rlf.Q_((0.12 + 0.1j) * np.eye(3), "ohm/km"),
    y_shunt=rlf.Q_(2e-4j * np.eye(3), "S/km"),
)

# Define a line between bus1 and bus2 (using g1 for the shunt connections)
line1 = rlf.Line(
    id="line1",
    bus1=bus1,
    bus2=bus2,
    parameters=parameters,
    length=rlf.Q_(2, "km"),
    ground=g1,
)

# Define a line between bus2 and bus3 (using g2 for the shunt connections)
line2 = rlf.Line(
    id="line2",
    bus1=bus2,
    bus2=bus3,
    parameters=parameters,
    length=rlf.Q_(2.5, "km"),
    ground=g2,
)

# Add a load on bus3
load = rlf.PowerLoad(
    id="load",
    bus=bus3,
    powers=rlf.Q_(np.array([5.0, 2.5, 0]) * (1 - 0.3j), "kVA"),
)

# Set the phase "a" of the first bus to the ground g1
g1.connect(bus=bus1, phase="a")

# Set the potential of the ground element g1 to 0V
pref = rlf.PotentialRef(id="pref", element=g1)

# Create a network and solve a load flow
en = rlf.ElectricalNetwork.from_element(bus1)
en.solve_load_flow()

# Get the ground potentials
# The potential of g1 is 0 as defined by the potential reference element
# The potential of g2 has no reason to be zero
en.res_grounds.transform([np.abs, ft.partial(np.angle, deg=True)])
# | ground_id   |   ('potential', 'absolute') |   ('potential', 'angle') |
# |:------------|----------------------------:|-------------------------:|
# | g1          |                       0     |                    0     |
# | g2          |                     230.949 |                  149.997 |

# As requested, the potential of the phase "a" of bus1 is zero
en.res_buses.transform([np.abs, ft.partial(np.angle, deg=True)])
# |               |   ('potential', 'absolute') |   ('potential', 'angle') |
# |:--------------|----------------------------:|-------------------------:|
# | ('bus1', 'a') |                     0       |                    0     |
# | ('bus1', 'b') |                   400       |                 -180     |
# | ('bus1', 'c') |                   400       |                  120     |
# | ('bus2', 'a') |                     4.19152 |                 -126.007 |
# | ('bus2', 'b') |                   398.525   |                  179.238 |
# | ('bus2', 'c') |                   397.913   |                  120.016 |
# | ('bus3', 'a') |                     9.41474 |                 -126.102 |
# | ('bus3', 'b') |                   396.739   |                  178.283 |
# | ('bus3', 'c') |                   395.28    |                  120.043 |

# The requested voltages of the voltage sources are respected
en.res_buses_voltages.transform([np.abs, ft.partial(np.angle, deg=True)])
# |                |   ('voltage', 'absolute') |   ('voltage', 'angle') |
# |:---------------|--------------------------:|-----------------------:|
# | ('bus1', 'ab') |                   400     |            6.31922e-19 |
# | ('bus1', 'bc') |                   400     |         -120           |
# | ('bus1', 'ca') |                   400     |          120           |
# | ('bus2', 'ab') |                   396.121 |           -1.25675     |
# | ('bus2', 'bc') |                   393.528 |         -120.45        |
# | ('bus2', 'ca') |                   399.634 |          119.467       |
# | ('bus3', 'ab') |                   391.499 |           -2.85404     |
# | ('bus3', 'bc') |                   385.429 |         -121.026       |
# | ('bus3', 'ca') |                   399.18  |          118.807       |

API Reference

class Ground(id: Id)

Bases: roseau.load_flow.models.core.Element

This element defines the ground.

Only buses and lines that have shunt components can be connected to a ground.

  1. Connecting to a bus:

    To connect a ground to a bus on a given phase, use the Ground.connect() method. This method lets you specify the bus to connect to as well as the phase of the connection. If the bus has a neutral and the phase is not specified, the ground will be connected to the neutral, otherwise, an error will be raised because the phase is needed.

  2. Connecting to a line with shunt components:

    To connect a ground to a line with shunt components, pass the ground object to the Line constructor. Note that the ground connection is mandatory for shunt lines.

Ground constructor.

Parameters:

id – A unique ID of the ground in the network grounds.

allowed_phases

The allowed phases for this element type.

It is a frozen set of strings like "abc" or "an" etc. The order of the phases is important. For a full list of supported phases, use print(<Element class>.allowed_phases).

property res_potential

The load flow result of the ground potential (V).

property connected_buses

The bus ID and phase of the buses connected to this ground.

connect(bus: roseau.load_flow.models.buses.Bus, phase: str = 'n')

Connect the ground to a bus on the given phase.

Parameters:

  • bus – The bus to connect to.

  • phase – The phase of the connection. It must be one of {"a", "b", "c", "n"} and must be present in the bus phases. Defaults to "n".

classmethod from_dict(data: JsonDict, *, include_results: bool = True)

Create an element from a dictionary created with to_dict().

Note

This method does not work on all classes that define it as some of them require additional information to be constructed. It can only be safely used on the ElectricNetwork, LineParameters and TransformerParameters classes.

Parameters:

  • data – The dictionary containing the element’s data.

  • include_results – If True (default) and the results of the load flow are included in the dictionary, the results are also loaded into the element.

Returns:

The constructed element.