Energy Transition

A: A fits the fast RoCoF with a shallow nadir: PLL instability can drop inverter output almost instantly, removing inertia-like support and forcing UFLS logic to act. B explains a deep nadir and slow recovery, not a sharp RoCoF spike. C could shed load, but it wouldn't line up with the inverter-rich period nor explain the RoCoF signature. D causes slow frequency wander; it doesn't create an abrupt event that trips protection within seconds.

A: The square with diagonal slash is the generic breaker symbol on many IEC-style SLDs; interrupting duty lives in the equipment list, not the graphic. B tempts people coming from motor control, but contactors are usually drawn with coil notation. C mixes up North American fused switch symbols with IEC conventions. D would normally be shown on the neutral leg with an earth symbol, not inline on the phase conductors.

A: Panels vent pressure; they don't address directed jet flames from choked hydrogen releases that can torch nearby assets. B and C are exactly what venting mitigates by giving pressure a weak path out. D is a civil load case unrelated to combustible gas safeguards and sits outside the cause–consequence chain being evaluated.

A: Hydrogen LHV is ~120 MJ/kg; multiply by 1,000 kg and divide by 3.6 GJ/MWh to land near 33 MWh before conversion losses. B forgets the MJ-to-MWh conversion. C bakes in downstream inefficiencies that weren't asked for and shrinks the figure too far. D confuses gravimetric energy with packaged system energy like batteries.