Building & field-validating a synchronous-generator EMT model.
For a synchronous generation plant, we built a full electromagnetic-transient model — generator, excitation system, stabiliser and protection — in PSCAD/EMTDC, then validated it against field measurements and assessed it against the a grid-code EMT model checklist under the connection grid code.
Why a connection like this needs a full EMT model.
Under the the connection grid code, generators connecting to the transmission system must provide an electromagnetic-transient (EMT) model that reproduces the plant's real dynamic behaviour — not a simplified phasor-domain approximation. For synchronous plant with fast excitation, power-system stabilisers and multi-stage protection, the time-domain detail matters: it is where sub-cycle voltage recovery, stabiliser damping and protection coordination actually live.
The added complexity here was the controllers. Machine ratings, reactances and inertia were available from the operator's PowerFactory model — but the excitation, the stabiliser and the protection had no equivalent in the phasor tool and had to be built from manufacturer data sheets directly in PSCAD. The model then had to stand up to the hardest test there is: agreement with measurements taken on the real machines.
Every control loop that shapes the transient response.
Select a subsystem to see what was represented and the parameters that define it. The full PSCAD control structure is shown in the figure below.
Synchronous machine dynamics
Excitation system (AVR)
Power system stabiliser
Excitation limiters — UEL & OEL
Generator protection module
Transformers & external grid
POI measurement & FFCI
Two independent checks, ending at the field measurements.
Confidence in an EMT model is earned, not asserted. The model was validated in two stages — first against the phasor-domain tool, then against reality.
PSCAD vs PowerFactory cross-validation
With the controllers de-activated, a 100 ms three-phase short circuit was applied on the HV side of the step-up transformer in both PSCAD and PowerFactory. Matching the bare machine response across the two solvers confirms the generator electrical and mechanical model is right before any control behaviour is layered on top.
PSCAD vs field measurements
With the full controllers active, simulated terminal voltage, field current, field voltage, active and reactive power were overlaid against measurements recorded on the real units across a range of operating points. Close agreement is what demonstrates the model reflects the actual plant — the core of the compliance case.
Field vs simulation — terminal-voltage step response
Illustrative of the validation method (Section 9.4). Measured and simulated traces overlay closely through the rise, overshoot and settle — the same comparison was run for no-load, on-load, unity-power-factor and maximum-leading operating points, and for fault ride-through.
The cases the model was put through.
Protection that trips like the real relay.
Ride-through is only half the picture. The model carries a configurable protection module so disturbances that should trip the unit actually do — with the right thresholds and the right time delays.
Over- and under-voltage and over- and under-frequency protection are each implemented as two independent stages, alongside a volts-per-hertz (over-flux) function. Every threshold and time delay is exposed on the component so the protection can be set to match the real generator's relay schedule — and each function was tested individually to confirm it operates and clears as intended.
Mapped to the the system operator EMT model checklist.
The model and its documentation were structured around the seven Basic Checks of the the system operator EMT model checklist. Expand each to see how it is met.
The Fast Fault Current Injection requirement is supported by the POI measurement block, which plots positive-sequence reactive current at the connection point during fault ride-through. The checklist's Detailed Checks are reviewed once the Basic Checks are accepted; the remaining categories — voltage control, fault ride-through and FFCI — are supported by the model framework, which is also structured so a turbine-governor model can be added for future frequency-response work.
All seven the system operator Basic Checks met — and field-validated.
Validated against field measurements
Simulated and measured responses agreed across the full operating envelope and through fault ride-through — the evidence a compliance reviewer looks for.
A checklist-ready package
Model, user guide and verification-and-validation report aligned to all seven Basic Checks, with FFCI plotting in place at the connection point.
Built to extend
Accessible controls for grid strength, taps, voltage steps and faults — and a framework ready for a governor model when frequency-response studies are needed.
One model in a full connection package.
An EMT model is a single deliverable in a grid connection. Velon has delivered multiple grid connection studies for clients — taking projects through the full set of studies a GB connection actually needs.
Planning a grid connection?
Send us the machines, the connection point and your target Gate 2 date — we'll tell you which studies it needs and how we'd evidence them.
Grid-connection and EMT studies, model validation and grid-code support for developers, OEMs, DNOs and TSOs.