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To represent the physical grid components, and the calculation results, this library uses 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 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

The type names in the hierarchy are exactly the same as the component type names in
the {py:class}`power_grid_model.power_grid_meta_data`, see [Native Data Interface](../advanced_documentation/native-data-interface.md)

This library uses a graph data model with three generic component types: node, branch, branch3 and appliance. A node is similar to a vertex in the graph, a branch is similar to an edge in the graph and a branch3 connects three nodes together. An appliance is a component which is connected (coupled) to a node, 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.
  • The node_1 and node_2 are connected by line_3 which is a branch (edge).
  • The 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. The source_5 is coupled to node_1 and the 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 model. For example, a power grid model can consist of both sym_load and asym_load. They are symmetric or asymmetric load components. On the other hand, the same model can execute symmetric or asymmetric calculations.

  • In case of symmetric calculation, the asym_load will be treated as a symmetric load by averaging the specified power through three phases.
  • In case of asymmetric calculation, the sym_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 {ref}user_manual/components:Appliance and {ref}user_manual/components: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 .