To represent the physical grid components and the calculation results, this library utilizes a graph data model. In this document, the graph data model is presented with the list of all components types, and their relevant input/output attributes.

Component Type Hierarchy and Graph Data Model

The components types are organized in an inheritance-like hierarchy. A sub-type has all the attributes from its parent type. The hierarchy tree of the component types is shown below.

graph LR base-->node base-->branch branch-->line branch-->link branch-->transformer base-->branch3 branch3-->three_winding_transformer base-->appliance appliance-->generic_load_gen generic_load_gen-->sym_load generic_load_gen-->sym_gen generic_load_gen-->asym_load generic_load_gen-->asym_gen appliance-->source appliance-->shunt base-->sensor sensor-->generic_voltage_sensor generic_voltage_sensor-->sym_voltage_sensor generic_voltage_sensor-->asym_voltage_sensor sensor-->generic_power_sensor generic_power_sensor-->sym_power_sensor generic_power_sensor-->asym_power_sensor classDef green fill:#9f6,stroke:#333,stroke-width:2px class node,line,link,transformer,three_winding_transformer,source,shunt,sym_load,sym_gen,asym_load,asym_gen,sym_voltage_sensor,asym_voltage_sensor,sym_power_sensor,asym_power_sensor green

Note

The type names in the hierarchy are exactly the same as the component type names in the power_grid_model.power_grid_meta_data, see Native Data Interface.

There are four generic component types: node, branch, branch3 and appliance. A node is similar to a vertex in a graph, a branch is similar to an edge in a graph and a branch3 connects three nodes together. An appliance is a component that is connected (coupled) to a node, and it is seen as a user of this node.

The figure below shows a simple example:

node_1 ---line_3 (branch)--- node_2 --------------three_winding_transformer_8 (branch3)------ node_6
 |                             |                                 |
source_5 (appliance)       sym_load_4 (appliance)             node_7

  • There are four nodes (points/vertices) in the graph of this simple grid.

  • node_1 and node_2 are connected by line_3 which is a branch (edge).

  • node_2, node_6, and node_7 are connected by three_winding_transformer_8, which is a branch3.

  • There are two appliances in the grid. source_5 is coupled to node_1 and sym_load_4 is coupled to node_2.

Symmetry of Components and Calculation

It should be emphasized that the symmetry of components and calculation are two independent concepts in the power-grid-model. For instance, a model can consist of loads of both sym_load and asym_load types, which is symmetry on component level. Meanwhile, both symmetric and asymmetric calculations can be run on the same model:

  • In symmetric calculation, an asymmetric loads will be treated as a symmetric load by averaging the specified power through three phases.

  • In asymmetric calculation, a symmetric load will be treated as an asymmetric load by dividing the total specified power equally into three phases.

Reference Direction

The sign of active/reactive power of the Appliance and Sensor depends on the reference direction.

  • For load reference direction, positive active power means the power flows from the node to the appliance/sensor.

  • For generator reference direction, positive active power means the power flows from the appliance/sensor to the node.