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RMS to EMT network reduction & validation

An EMT study can't carry a whole transmission network, so the wider system is reduced to an equivalent that behaves the same at the study boundary. We turn a large RMS model into an EMT-ready one without losing the dynamics the study depends on.

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Frequency scan · full against reducedIllustrative
1101001k101001k2kf (Hz)|Z| (Ω)range checked
Impedance error100 Hz to 1 kHz–%limit 5%
Run timeper EMT case– minlimit 30 min
Cases a dayin 8 hours–at least 16
When it's needed

When you need it.

  1. A detailed EMT study needs a runnable model of a very large grid.
  2. A PowerFactory or PSS®E model has to move into EMT.
  3. The boundary and the equivalent have to be justified to a reviewing operator.
  4. Several EMT studies will reuse one consistent, validated reduced network.
Method

How we run it.

  1. 01

    Boundary

    Decide what stays detailed and where the reduction starts.

  2. 02

    Prepare

    Clean up the source RMS model and pull the data the equivalent needs.

  3. 03

    Reduce

    Form the equivalent, Ward-type for example, keeping fault level and frequency behaviour.

  4. 04

    Validate

    Compare reduced and full models on the responses the study needs.

  5. 05

    Document

    Write up the boundary, the equivalent and the checks as evidence.

Tools and scenarios

Every scenario through every study.

  • PowerFactory · PSS®ERMS source
  • PSCADEMT target
  • Velon Suites toolkitNetwork reduction
Frequency scanLoad flow matchFault level matchEMT run time
Peak demand
Minimum demand
Outages near the boundary
High renewables
Network changes
New connections

Outages near the boundary · Frequency scanWith a nearby line out, the reduced model missed a resonance at 700 Hz. Two more buses at the boundary bring it back.High renewables · EMT run timeKeeping every converter in detail took 50 minutes a case. Equivalents for distant plants cut it to 12.Network changes · Load flow matchA new circuit changed the load flow by 4%. The script rebuilt the reduction in an hour.

21 checks · 3 led to a change · every case scripted and rerunnable
Deliverables

What you get.

  • ModelAn EMT-ready reduced network model
  • EvidenceChecks comparing reduced and full models at the boundary
  • BoundaryA written case for the study boundary that holds up in review
  • FilesReusable, version-controlled model files

How we check it

We check the reduced model against the full one on the specific responses the EMT study relies on, and record the boundary choice so a reviewer can see what was kept, what became an equivalent, and why.

Selected work

Related case studies.

Case 04 · RMS to EMTNetwork reduction for large RMS modelsThree tools that get a wide-area RMS model ready for EMT.Case 03 · SSO and compliance40 MW battery: SSO screening and NESO complianceImpedance scan, Nyquist, voltage injection, FRT and FFCI from one model.
FAQ

Questions engineers ask.

Why not just model the whole network in EMT?
EMT is computationally heavy; a full transmission model would be impractical to run and maintain. Reduction keeps the study area detailed while representing the rest by an equivalent that preserves the relevant behaviour.
How do you know the equivalent is good enough?
By validating it against the full model for the responses that matter at the boundary (short-circuit behaviour and the frequency range of interest), and by documenting where the equivalent is and isn't valid.
Can the reduced network be reused?
Yes. A validated, version-controlled equivalent can underpin several EMT studies, which is part of what the Velon Suites toolkit is designed to support.
Next step

Have a study like this coming up?

Discuss a project [email protected]

Related: Consultancy hub · Network reduction case study · PSCAD / EMT studies · The Velon Suites