Large RMS models aren’t built for EMT.
Wide-area RMS models carry tens of thousands of buses, node-breaker substations, split-up circuits and distribution detail that an EMT simulation has no use for. These tools get the model ready for conversion, then show with measurements where the EMT study boundary should sit.
- No.
- 04
- Type
- RMS to EMT
- Client
- Internal tooling
- Our role
- Tool development and boundary studies
- Inputs
- PowerFactory, PSS®E
- Output
- EMT-ready model for PSCAD
- Part of
- Velon Suites
- Status
- In use
More connections now need EMT studies before an offer is made, as inverter-based generation and very large loads such as data centres join the transmission system. The studies are only as good as the model behind them, and getting a wide-area RMS model into EMT with a boundary the system operator accepts is usually the slow part.
Three things stop a wide-area RMS model converting to EMT.
Too big for the EMT solver
Tens of thousands of buses, deep distribution feeders and neighbouring networks. None of it matters to the study, but all of it slows the simulation. It has to be reduced, not ignored.
Topology the converter rejects
Node-breaker substations with hundreds of switch nodes, multi-segment circuits, duplicate IDs and out-of-service clutter. Any of these can make an RMS to EMT importer fail before a simulation starts.
Boundaries drawn by habit
Even after a clean conversion, the study area is usually drawn by judgement. Too wide wastes solver time; too tight distorts the impedance seen at the POI. Neither holds up in a system-operator review.
Part 01 fixes the first two in the RMS model, before anything is converted. Part 02 fixes the third by placing the boundary with a repeatable measurement.
DSO network reduction
The distribution network has no place in an EMT model. Aggregate it from the bottom up, climbing toward the study area until a second connection (a leakage path) blocks a clean cut, then place a Ward equivalent that keeps power flow and short-circuit level exact.
Open tool →02Substation collapse
A node-breaker substation can have hundreds of switch nodes that the converter will reject. Collapse each station to its electrical nodes: one bus per closed group, split where a coupler is open.
Open tool →03Branch merge & cleanup
Multi-segment lines, duplicate IDs, voltage controllers left pointing at removed buses, out-of-service clutter. Each one can make the importer fail, and this step clears them before conversion.
Open tool →Impedance-scan reduction
The study area has to reproduce the full network’s harmonic impedance at the POI. Grow the boundary one bus at a time, re-scan each time, and stop when the reduced scan matches the reference within the agreed threshold.
Open tool →05Voltage-dip screening
Apply a three-phase fault at the connection point and find where residual voltage recovers above the operator’s threshold. That boundary is the study area for FRT and protection screening.
Open tool →Five tools, one pipeline.
Climb until a leakage path stops you, then place a Ward equivalent.
A large transmission and distribution model in PowerFactory can carry far more nodes than an EMT study needs, and an importer brings every one of them across. This tool reduces the distribution network first, in the RMS model. It aggregates feeders upward until a leakage path (a second connection back into the retained network) blocks a clean cut, and places a Ward equivalent there that keeps power flow and short-circuit level true. Click any leakage tie to add or remove it and watch the boundary re-solve.
Four-busbar substation → single bus.
A typical UK 132 kV substation: two double-busbar sections (north and south), each with a main and reserve bar joined by a bus coupler, and the two sections linked by section couplers on both bars. With every coupler closed it is one electrical node, so the whole station collapses to a single busbar. Open any coupler and the station splits along it. Click any coupler to open or close it, or click a bay to move it.
Clear every barrier before the converter sees it.
DSO reduction and substation collapse deal with size and topology. This step deals with the rest: the structural errors and missing housekeeping that make an RMS to EMT importer reject a model before anything can run.
Multi-segment branch → single line
A circuit built from many series line elements becomes one equivalent π, with the same impedance and charging and a fraction of the nodes, before it reaches the importer.
Unique element identifiers
Every bus, line and transformer keeps a stable, unique ID that can be traced through the conversion back to the source.
Station controller handling
Voltage and reactive station controllers are resolved and re-pointed so the reduced model regulates exactly as the original did.
Out-of-service cleanup
Open switches and out-of-service elements are stripped, so no dead branches or noise cross into the EMT model.
Connectivity & island checks
Dangling terminals and isolated islands are detected and flagged before they trip the importer or distort the solution.
Load & generation aggregation
Downstream demand and embedded generation are lumped onto the retained boundary, preserving the net injection.
Grow the boundary until the scans match.
Starting at the point of interconnection, the boundary grows outward one bus at a time, and the harmonic impedance is checked against the full network at every step. As soon as the reduced scan sits on the reference within threshold, it stops. That is the smallest study area that still gives the right impedance at the POI. Watch the boundary grow on the network while the scan locks on beside it.
The boundary sits one bus from the POI. Far too tight: the impedance match is poor, so the automation keeps expanding.Reduction stops here · study area exported for EMT
Apply the fault. Watch the dip spread.
A three-phase fault at the point of interconnection pulls the voltage there to zero. Further out, residual voltage recovers. The boundary sits where it crosses the operator’s threshold, far enough out that remote inverters never see a fault-ride-through trigger. Move the controls to see the study area change.