Energy Transition

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.

A: Grid-forming control sets voltage and frequency directly, giving inertial response without a PLL chase. B still hinges on PLL behavior, the weak link during fast transients. C helps voltage, not active power–frequency coupling. D adds inertia but doesn't let the inverter itself arrest frequency at the required speed.

A: Hydrogen speeds up flame kinetics and narrows stable operating windows; during ramps the control system can cross into blowout or dynamics zones. B would trend slowly and not correlate with ramps. C links to mechanical load, not fuel composition. D would trip on electrical faults, not after combustion alarms.

A: A mismatch means the instrument could be the weak point during pressure excursions; mitigation or re-rating is needed. B overlooks surge and isolation valve failures. C treats a design limit as optional, which invites MOC trouble. D misreads code intent; pressure-containing instrument bodies still have MAWP.

A: Clean agents knock down flames but don't remove heat inside cells; runaway can keep propagating internally. B and D are exactly where clean agents help by interrupting combustion. C is a mechanism of the safeguard, not a remaining hazard.

A: 1,000 kg/day at 50 kWh/kg is 50,000 kWh/day; divide by 24 h to land just over 2 MW. B drops a factor of four by mis-averaging. C treats energy per day as instantaneous power. D piles on contingencies without numbers, overshooting the order needed.

A: A provides a voltage reference, manages transformer inrush via sequencing, and sustains the island until generation picks up. B still needs another source to form the grid. C offers vars but no active power for cranking loads. D gives inertia and vars, yet can't energize a dead bus on its own.