What was going wrong
The planning consultant had delivered a steady-state load flow study showing the corridor was technically feasible. But the study used RMS stability models that treat HVDC as a simple power injection. It did not model the converter controls, did not simulate DC pole-to-ground faults, and did not examine what happens when three offshore wind farms trip simultaneously and the remaining inverters must hold grid voltage without synchronous support.
The grid operator knew the study was insufficient for construction, but did not have the in-house expertise to challenge it or produce what was missing.
How we ran it
We rebuilt the model from component physics: modular multilevel converter (MMC) switching behaviour, DC cable travelling-wave dynamics, AC filter interactions, and protection relay logic. We ran electromagnetic transient (EMT) simulations in PSCAD/EMTDC at 10 microsecond time step, then cross-checked key results against published field measurements from three comparable commissioned HVDC links.
Every protection setting was derived from fault current waveforms, not from rule-of-thumb tables. Every control parameter was tested against pole faults, AC faults, and commutation failures at multiple operating points.
Where it landed
The grid operator received a complete design package: converter station single-line diagrams, DC protection philosophy with relay settings, EMT study reports with waveform evidence, and grid-forming control specifications tested against the actual fault scenarios the corridor would face.
The package was submitted to the regulator and accepted without revision. Construction tender was issued six months later.
