Small steam turbines and industrial engines ask their governors for different things, which is why Woodward's catalog holds both the TG-13 — a self-contained mechanical-hydraulic governor with droop and its own oil sump — and the ProAct II digital electronic system driving high-output actuators. Matching architecture to machine is the whole exercise: the TG-13 survives where power and instruments are unreliable; the ProAct II wins where precision and integration are the product.
The TG-13: governance without a power cord
The TG-13 (8516-039 class) drives from the turbine shaft, carries roughly 1.7 liters of its own oil, and holds speed on flyweight-hydraulic physics with droop characteristics. On small mechanical-drive turbines — pumps, fans, small generator sets in austere sites — its independence is the specification: speed holds through electrical events that would blind any electronic control. The costs are mechanical maintenance and droop-class accuracy; on a machine whose process tolerates both, that trade is simply correct.
The ProAct II: precision with an actuator budget
The ProAct II (9907-1290 class) is the digital route: precise speed and load control, configurable dynamics, and a high-output driver feeding ProAct electric actuators at up to 200 mA. It is the choice when the turbine feeds a process that measures the governor's error — extraction control, tight frequency on a process generator, or integration with a plant DCS through standard interfaces. Its prerequisites are honest: reliable control power, a speed sensor, and commissioning time for the dynamics.
The decision rule
Austere site, mechanical-drive duty, no power reliability: TG-13, and service it like the engine it lives on. Process-critical, electrified, integration-hungry: ProAct II. The same logic splits Woodward's whole governor family, and both routes coexist in one plant without ceremony — the control-room sees them as two signal conventions, not two philosophies.
Can a TG-13 hold isochronous load share?
Not in the modern sense — droop is its native character, and sharing implies the electronic loop's precision. Plants needing isochronous sharing upgrade the governor; the turbine does not care, but the bus does.
What wears on the TG-13?
Oil quality and linkages — the hydraulic circuit is the machine. Clean oil and annual service keep it honest for decades; neglected, it degrades exactly as predictably as the recipe says.
