Electric distribution
MV feeders to meter
The Electric skill turns Nexma into a medium-voltage distribution-design platform. It models the network from substation to meter, validates voltage drop end to end, and balances three-phase load across feeders. The organizing rule here is the voltage budget — every routing and sizing decision answers to it.
What this skill models
The ontology captures a distribution feeder with the entity types, link types, and constraints a distribution planner expects.
- Entity types.
Substation,Transformer,Switchgear,Panel,Meter,ProtectionDevice,CableTray, andGroundingEquipment. Each carries typed properties — kVA rating, impedance, fuse curve, conductor size. - Link types.
HVFeeder,LVDistributionCable,ServiceDrop, andGroundWire. Conductors carry ampacity, voltage class, and ICEA stranding. - Key constraints. Voltage drop capped at 5% end to end; thermal capacity bounded by conductor size; three-phase load balanced within plus or minus 10%; and ground-fault clearing times that stay inside protection coordination.
The ontology ships the engineering reference data a planner needs: IEEE conductor tables, NEC ampacity matrices, transformer impedance defaults, and fuse and recloser curves.
What Jax can do
Jax reasons electrically because the Skill binds its capabilities to this ontology.
- Generate feeder loops. "Lay a 15kV feeder loop through this neighborhood. Cap voltage drop at 4%. Use 1/0 ACSR on the trunk and #2 on laterals." Jax derives load points from OSM footprints with land-use multipliers if no meter layer exists.
- Size transformers for diversified load with a chosen safety margin.
- Balance phases across single-phase laterals to hold imbalance within IEEE recommendations.
- Coordinate protection — proposes fuse and recloser curves that nest correctly so the nearest device clears first.
- Validate voltage drop, thermal capacity, and ground-fault coordination, flagging violations inline.
The voltage-drop solve and phase rebalance run through the Nexma MathEngine, writing results back to the world model so transformer loading updates the moment Jax finishes.
Tip: Lock the feeder voltage and the trunk conductor before asking Jax to balance phases. Voltage drop is dominated by trunk impedance, so settling that first keeps the phase-balance pass from undoing the voltage solve.
Constraints and standards
The skill enforces the rules a distribution design must satisfy to be coordinated and safe.
| Concern | Rule enforced | Standard |
|---|---|---|
| Voltage drop | 5% maximum end to end | IEEE distribution practice |
| Ampacity | Thermal limit by conductor | NEC (NFPA 70) / ICEA |
| Phase balance | Within plus or minus 10% | IEEE recommendation |
| Short circuit | Fault levels within rating | IEC 60909 |
| Protection | Clearing times coordinated | IEEE coordination |
Export targets include CYME, SynerGEE, and GeoJSON from Project to Export.
Out of scope today: transmission planning above 69kV, transient stability analysis (steady-state only), and substation primary-equipment layout such as busbars and breakers.
Where to go next
- Gas distribution — pressure staging with the same network model.
- Water distribution — the budget-and-validate pattern for hydraulics.
- Skills overview — the full catalog.
- Nexma MathEngine — the solver behind the voltage and phase passes.