Generator Gas Replacement During Startup and Shutdown: Full Procedure and Key Safety Precautions

Generator Gas Replacement During Startup and Shutdown: Full Procedure and Safety Precautions

Generator gas replacement must be carried out only after the generator has passed its air-tightness test and its insulation is qualified. The replacement can be performed while the rotor is stationary or running on the turning gear. This article walks through pre-checks, precautions, the startup and shutdown replacement processes, and routine hydrogen makeup.

1. Pre-Replacement Checks

• Put the turbine lube oil system and seal oil system into service.
• Carry out a full inspection of the hydrogen system to confirm replacement conditions are met.
• Before replacement, stop the circulating fan and isolate the online humidity meter and purity meter.
• Tools: power reel, copper wrench, copper hook (never use iron wrenches or hooks), and lamps (for baking piping and valves when using CO2).

2. Key Precautions During Replacement

1. No hot work is allowed in the surrounding area during gas replacement.
2. Copper wrenches and hooks must be used — iron tools are forbidden to avoid sparks.
3. When working around the hydrogen system, the site must be well ventilated and well lit.
4. Closely watch that the oil-hydrogen differential pressure tracks automatically and correctly; if not, adjust manually.

3. Startup Gas Replacement

Step 1 — Replace air with CO2:

1. Connect the CO2 cylinder outlet to the manifold interface.
2. Open the generator CO2 inlet valve.
3. Slowly open the CO2 discharge valve and let CO2 enter the generator, carefully controlling the charging rate.
4. Maintain the generator internal gas pressure at 0.02–0.03 MPa during replacement.
5. Repeatedly purge the dead corners, sampling valves and oil-water detector drains. When CO2 purity reaches ≥ 85%, purity is qualified and CO2 replacement is complete.

Step 2 — Replace CO2 with hydrogen:

1. Drain the CO2 from the generator.
2. Contact the hydrogen plant operator and confirm the makeup method.
3. Maintain the generator internal gas pressure at 0.02–0.03 MPa during replacement.
4. Control the hydrogen charging rate to prevent a hot spot from excessive hydrogen velocity at pipe reducers, which could cause an accident.
5. Repeatedly purge the dead corners, sampling valves and oil-water drains. When hydrogen purity reaches ≥ 96%, purity is qualified and hydrogen replacement is complete.
6. Put the hydrogen dryer, circulating fan, purity meter, humidity meter and generator insulation device into service.

4. Shutdown Gas Replacement

1. First replace the generator hydrogen with CO2; purity ≥ 95% is qualified.
2. Then replace the generator CO2 with air; purity reaching 15% is qualified.
3. The shutdown process is similar to startup — only the required purity differs at each stage.

5. Hydrogen Makeup During Operation

• Open the hydrogen makeup valve.
• Contact the hydrogen plant for makeup.
• Adjust the makeup pressure.
• When hydrogen pressure is sufficient, contact the hydrogen plant to stop makeup; after the makeup pressure drops, close the makeup valve.
• Control the makeup rate throughout the process.

6. Summary of Key Points