Startup/Shutdown Sequences

A Generic Sequence Across Plant Types

Every plant type in this course starts and stops differently in its specifics — a simple cycle gas turbine start looks nothing like a coal boiler light-off in terms of timing and equipment involved. But the underlying sequence of phases is remarkably consistent across all of them. This module covers that generic structure; refer back to the plant-type modules (BTA-105 through 107) for the equipment-specific details of each phase.

Cold, Warm, and Hot Starts

Not all starts are equal. A cold start begins from a fully cooled-down state after an extended outage; a hot start begins shortly after shutdown, while equipment is still warm. Hot starts are faster because less time is needed to bring metal temperatures up gradually, but they carry their own risks if thermal transients aren't respected. Warm starts fall in between. Every start procedure accounts for which category applies, adjusting timing and hold points accordingly.

Permissives and Interlocks

Before any start sequence can proceed, a series of permissives — conditions that must be satisfied — are checked automatically by the control system: lube oil pressure established, cooling water available, no active trips, required equipment lined up correctly. Interlocks are the logic that prevents a step from occurring unless its permissives are met, and prevents dangerous combinations of conditions (like fuel admission before adequate purge). These aren't obstacles to work around — they exist because someone, at some point, learned the hard way what happens without them.

The Phases

• Pre-start checks — verifying equipment lineups, permissives, and readiness before the sequence begins. AOs often perform field verification of valve positions and equipment status feeding into this checklist.
• Start initiation — the control system (or operator) commands the sequence to begin; starting devices engage, purge cycles run where applicable.
• Warm-up/acceleration — the unit brings itself up to operating speed or temperature gradually, with built-in hold points at critical thresholds to allow thermal equalization.
• Synchronization and loading — once at speed, the generator synchronizes to the grid and load is raised gradually to the target setpoint, following a loading rate that respects thermal stress limits.
• Steady-state operation — the unit settles into normal, sustained operation — this is where most of the "rounds" content from this entire course applies day to day.
• Unloading/shutdown — for a normal (not emergency) shutdown, load is reduced gradually, following its own rate limits, before the unit is finally taken offline.
• Cooldown and securing — equipment cools gradually (turning gear often continues on large turbines to prevent uneven cooling and rotor bowing), and systems are secured per procedure for the outage.

Why Patience Matters

Every plant-type module in this course mentioned some version of the same lesson: rushing a start or shutdown, particularly around thermal transients, risks real equipment damage that dwarfs the time saved. A turbine rotor that needs turning gear time to straighten from thermal bow, or a boiler drum that needs a controlled heat-up rate — these aren't arbitrary conservatism. The cost of patience during a start or shutdown is measured in minutes or hours; the cost of impatience can be measured in a very expensive piece of rotating equipment.