Network Area Definitions

This page details the different implementations of network areas and how their net positions are computed.

Border-based Implementations

Border-based areas compute the net position by looking at the “perimeter” of the area. The net position is the sum of active power flows leaving the area through its boundaries.

Implementations

  • BorderBasedCountryArea: Defined by a list of Country objects.

  • BorderBasedVoltageLevelsArea: Defined by a list of voltage level IDs.

Net Position Calculation

For border-based areas, the net position is calculated as:

\[NP = \sum P_{leaving\_flow}\]

This includes:

  • Flows on Tie lines (Boundary lines).

  • Flows on Lines and HVDC lines where one end is inside the area and the other is outside.

  • For voltage-level based areas, it also includes Transformers (two-windings and three-windings) connecting a voltage level inside the area to one outside.

The flow is counted positively if it leaves the area. For AC lines, the flow is usually calculated as \((P_{side1} - P_{side2}) / 2\) to account for losses, oriented from the internal side to the external side.

Warning: If a HVDC line connects a first synchronous component with load flow convergence to another non-synchronous component with load flow divergence, the flow is only computed on the side with load flow convergence. There is no split of the losses. This approximation is used to simplify the calculation and provide a reasonable estimate of the net position on the converged synchronous component. But the implementation relies on the power flow result at the conversion stations of the HVDC lines to determine if a divergence has occurred. It can lead to inaccuracies with other load flow implementations.

Injection-based Implementations

Injection-based areas compute the net position by summing all power injections located inside the area.

Implementations

  • InjectionBasedCountryArea: All generators and loads within the specified countries.

  • InjectionBasedVoltageLevelsArea: All generators and loads within the specified voltage levels.

Net Position Calculation

The net position is calculated as the sum of internal generations minus the sum of internal loads:

\[NP = \sum P_{generators} - \sum P_{loads}\]

Specifically, it uses:

  • Generator.getTargetP() for productions.

  • Load.getP0() for consumptions.

Load Flow Balancing

Both types of implementations support an optional parameter subtractLoadFlowBalancing in the getNetPosition(boolean) method.

Why is it needed?

In a load flow study, the calculated physical flows on lines might not perfectly match the initial target injections due to:

  • Network losses.

  • The presence of a slack mechanism (single slack bus or distributed slack) that absorbs the global mismatch.

  • Differences between target power (targetP, p0) and actual computed power (p) after load flow convergence.

Effect on calculation

When subtractLoadFlowBalancing is set to true:

  1. For Injection-based areas: Currently, the implementation might ignore this flag or handle it by returning the raw injection balance. (Refer to specific implementation details).

  2. For Border-based areas: The net position is adjusted by the local “mismatch” found within the area:

    \[NP_{adjusted} = NP_{physical\_borders} - (\sum (P_{target} - P_{computed}))\]

    This helps in aligning the border-based net position with the intended injection-based balance by removing the influence of the load flow’s balancing mechanism (like slack adjustments) if they occurred inside the area.