PVcase

Complex MV Designs

PVcase enables the creation of complex Medium Voltage (MV) circuit designs by using workarounds such as creating multiple colocated Grid Connection points to simulate multiple MV bays at a single Point of Interconnection, employing "Transformer" objects combined with multiple Grid Connections to represent MV Dead Break Junction Boxes with Y branching, and adjusting labels and Single Line Diagrams accordingly to ensure accurate cable length calculations and correct Bill of Materials exports.

PVcase allows users to easily create MV Circuits in a linear or loop fashion. For more complex designs—such as those with multiple interconnection bays at the Point of Interconnection (POI), MV Junction Boxes, or Y branches at certain Transformers—some workarounds are necessary.

1. Multiple MV Bays at Grid Connection Point

One Grid Connection point cannot directly host multiple MV branches. The workaround is to create multiple Grid Connection points, one for each MV circuit connecting to the Substation. Each of these Grid Connections can be colocated and considered a Substation Bay.

  • The Overview will display the Bays as Grid Connections, but the number label in the Model Space can be modified to include “Substation Bay.”
  • The Single Line Diagram (SLD) will show the new labels, which can be further edited by exploding the SLD. Cable lengths for all MV Circuits will be calculated correctly.
  • The exported BOM Excel file will show the correct lengths and can be post-edited for proper naming conventions.

2. Y Branching at MV Dead Break Junction Boxes

Dead Break Junction Boxes are used to combine two or more MV lines into one, commonly when multiple MV lines converge and then go to the Substation. To generate an MV paralleling Junction Box:

  • Use the Grid Connection feature.
  • Generate a “Transformer” at the location where the Junction Box is to be placed, then create two or more Grid Connection points from there.
  • The Overview will show the Junction Box as a “Transformer” and the Junction Box Bays as Grid Connections, but number labels can be modified in the Model Space to show “Junction Box” and “JB Bay.”
  • The SLD will reflect the new labels, and cable lengths for all MV Branches will be calculated correctly.
  • The exported BOM Excel file can be post-edited for naming conventions.

3. Y Branching at MV Transformers

It is common to have two incoming (and one outgoing) MV voltage feeders at certain MV skid transformers. PVcase Transformers can only be linked in an open or closed MV line, not branched into multiple lines. The workaround is:

  • Create main lines of transformers to the Substation Bay.
  • Add a “Grid Connection” at specific transformers for each extra branch needed.
  • The Overview will show extra branches as Grid Connections, but the number label can be moved, eliminated, or modified to show “XFR Branch.”
  • The SLD will show the new labels, and cable lengths for all MV Branches will be calculated correctly.
  • The exported BOM Excel file can be post-edited for naming conventions.

4. Transformer with Multiple Co-located Central Inverters

Due to the increasing size of PV Transformer blocks and the limited MW capacity of commercially available Central Inverters, most MV skids/containers now have more than one co-located Central Inverter. This setup offers benefits such as more MPPTs, higher reliability, and more space for DC inputs.

To design such systems in PVcase:

  • Instead of using the standard “DC Combiner - Central Inverter” system type, select “DC Combiner - Inverter - Transformer.”
  • Quantities in the Configuration section should be based on the original numbers, divided among the co-located Central Inverters.
  • Change the Placement type from “Trench adjacent” to “Centralized.”
  • Generate the Electrical devices, selecting which strings are linked to each inverter (or allow the software to assign automatically).
  • The new block will appear in the Overview and SLD as a Transformer with two or more inverters associated.
  • DC and HV cabling can be generated as usual, and AC cabling at the skid/container can be added if needed.

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