Step Transformers for Distribution

While distribution transformers mediate between the MV and LV voltage classes, step transformers mediate between two different VoltageGroup values that both lie within the range of the MV voltage class.

Recommended Configuration

• Unlike distribution transformers, which tap power from a primary (MV) circuit and sends it to a secondary (LV) circuit, a step transformer sits in the path between two MV circuits of differing VoltageGroup values. For this reason, a step transformer is always expected to be positioned at an endpoint that is shared by two primary conductor features of different voltage levels. No special tap feature is needed for this arrangement.

• Similar to distribution transformers, a step transformer can contain a single three-phase unit that is for a symmetrical three-phase bank. It can also contain up to three single-phase units, for a one-phase transformer or if it has different sized units per phase.

Step Transformer Diagram

Open Delta Transformers

Recommended Configuration

• We model an open delta transformer as a transformer bank that contains two units, each carrying a 2-phase value in the PhasesNormal attribute, such as AB, to indicate the pair of phases connected across the primary winding of each unit.

• The derived phase will be assigned to both transformer units.

Product Limitation

• UN phase propagation will not properly propagate the phase from a two-phase MV Conductor to three-phase LV Conductor

• ArcFM Designer XI does not support an open delta transformer.

Unbalanced: Open Delta Transformer

CSP Transformers

CSP Transformers that contain fuses used without ADMS (Option 1)

Some transformer units include protective devices on either the primary side, secondary side, or both. A transformer may have a fuse in line with the primary winding, for example. If the customer is not implementing ADMS, the ArcFM UN recommendation is to map these attributes to the Asset Group Asset Type used when for a CSP type of Transformer; either RatedCurrent, MaxInterruptingAmps, or FuseLinkType. The transformer can be modeled as either in-line or tapped.

CSP Transformers that contain fuses and used with ADMS (Option 2)

ADMS requires the fuse to be present for CSP Transformers. These fuses must be spatial. With this approach, a simple configuration technique can enable the GIS/ADMS integration infrastructure to map the GIS representation of a transformer with a contained fuse into the ADMS representation required to support the ADMS functions that depend upon the fuse data.

Required Configurations

• Use a spatial feature in the ElectricDevice feature class to represent the transformer.

• The transformer must in the E:Transformer – Inline category.

• The transformer unit records in the electric JunctionObject table must have an asset group and asset type that belong to the E:Transformer and E:Unit network categories.

• Use a separate spatial feature in the ElectricDevice feature class to represent the fuse.

• Junction-to-Junction connectivity cannot be used to connect the fuse to the primary line, or to the transformer. You must use a conductor connector. (Tip: If using Designer XI, the user can create a template that makes placing CSP Transformer easy).

CSP Transformer requirement in ADMS

A three-winding transformer is modeled as a device that has three terminals, where each terminal is connected a circuit of a different voltage level. This design is currently under review by the development team.