Pre-Start Checks & Permissives
Where Every Prior Track Converges
Module 7.1 covered how starting metal temperature shapes the warm-up sequence. Before that sequence can even begin, a set of pre-start permissives must all be satisfied — and each one traces back to a specific concept from earlier in this course. This module is where nearly everything the course has covered converges into a single decision point.
Five Key Permissives
Lube oil system ready: before any shaft rotation begins, lube oil pressure must be established and confirmed adequate. Bearings need oil film support (Module 2.4) from the very first moment of rotation — there's no acceptable window where the shaft turns without adequate lubrication.
Turning gear engaged, rotor even: operators confirm turning gear has run long enough to verify the rotor is running true, with no existing bow from uneven cooling (Module 2.6) still present. Attempting to roll up with an existing bow risks exactly the vibration and mechanical problems adequate turning gear time is meant to prevent.
Simply having turning gear engaged doesn't guarantee the rotor has actually run long enough to work out any bow. This permissive confirms both engagement and sufficient elapsed time — not just that the gear is turning, but that it's been turning long enough.
Condenser vacuum established: adequate vacuum must be confirmed before admitting steam, protecting the LP turbine from the back-pressure and windage heating concerns behind Module 5.3's low vacuum trip. Starting without adequate vacuum risks reaching the exact condition that trip exists to catch — this permissive prevents ever reaching that risky state in the first place.
Trip system armed and tested: the entire trip system (Track 5) must be confirmed armed and, per Module 5.4's periodic testing, verified to have passed recent testing. Protection must be demonstrably functional before the machine is allowed to operate — the practical convergence of Track 5's entire verification-not-assumption philosophy at a single decision point.
Drains open: steam line and casing drains must be confirmed open, allowing accumulated condensate to drain away rather than being carried into the turbine as water. This connects directly to Module 5.3's water induction discussion — condensate accumulating during an outage poses exactly the risk that trip covers, and open drains during startup is the preventive measure that keeps it from ever reaching the turbine.
AND-Logic, Not OR-Logic
Unlike trip logic (Module 5.2), which uses OR-logic where any single trip input can act, pre-start permissive logic uses AND-logic — every single condition must be satisfied simultaneously before startup is allowed to proceed. This is a deliberate contrast: starting requires everything to be right, while tripping requires only one thing to be wrong. The asymmetry makes sense given the very different consequences of a false start versus a missed trip.
Trip logic (Module 5.2): OR-logic, any single danger signal acts. Permissive logic: AND-logic, every readiness condition must be true. Both logic structures are correct for their purpose — protection should trigger easily, but starting should require full confidence across every system.
Why Permissives Aren't Optional
Each permissive exists because of a specific, real failure mode covered elsewhere in this course. Bypassing or overriding one doesn't eliminate the underlying risk — it just removes the safeguard specifically designed to catch it. Lube oil (Track 6), rotor bow (Module 2.6), condenser vacuum (Module 5.3), trip system readiness (Track 5), water induction (Module 5.3) — permissives aren't arbitrary bureaucratic hurdles. They're the accumulated lessons of this entire course, applied at the single moment that matters most.