Connecting Components

One of the main goals of a network model, is specifying how constituent components are connected together. The patterns explained here, are equally applicable to the engineering and mathematical data model.

The available connections of each component connect to bus terminals. Take for example a bus with four terminals, terminals=["a","b","c","n"].

Node objects

Node objects always connect to a single bus (and perhaps also the universal ground, as can be the case for shunts). Therefore, they always have at least two key fields controlling the connectivity: bus and connections. Most node objects also have a configuration field, which affects the interpretation of the values supplied in connections. We will illustrate this for loads below.

Loads

A multi-phase load consists of several individual loads, the number of which is implied by the length of properties such as pd_nom, qd_nom etc. The table below illustrates how the length of the field connections and the value of the field configuration determines the layout of the load.

connections	configuration==WYE	configuration==DELTA
2
3
4		undefined

For example, we wish to connect a wye-connected load consisting of 2 individual loads (|connections|=3 and configuration=WYE) to our example bus with four available terminals. If we specify connections=["a","c","n"], this leads to

.

Edge objects

Edge objects connect two buses (except for generic transformers, which can connect N buses). Therefore, they have the fields

• f_bus and f_connections, specifying the from-side bus and how the object connects to it;
• t_bus and t_connections, specifying the same for the to-side.

Lines

A line can have a variable number of conductors, which is implied by the size of the fields rs, xs, g_fr, b_fr, g_to and b_to. The fields f_connections and t_connections should specify for each conductor, to which terminals it connects. The figure below illustrates this for a line with 2 conductors,

.

Transformers

Transformers also have a configuration field. For

• generic transformers, this is specified per winding, and configuration is therefore a vector of ConnConfig enums (WYE or DELTA);
• AL2W transformers however are always two-winding, and the secondary is always wye-connected. Therefore, configuration is a scalar, specifying the configuration of the from-side winding.

Generic transformers have a field buses, a Vector containing the buses to which each winding connects respectively (these do not have to be unique; a split-phase transformer is typically represented by having two windings connect to the same bus). The AL2W transformer however, since it is always two-winding, follows the f_connections/t_connections pattern.