TL;DR
Declining hydrogen purity or elevated makeup demand signals a leak. Check the shaft seal oil system first since shaft seals are the most common hydrogen leak path on large generators.
What you might see
- hydrogen purity reading declining
- hydrogen makeup rate above normal
- hydrogen detector alarm inside the generator hall
- shaft seal oil system consuming more oil than normal
Likely causes
Degraded shaft seal oil film allowing hydrogen to migrate past the seal
Cracked or corroded flange gasket on the generator casing
Faulty hydrogen control valve seat allowing uncontrolled purge
High hydrogen pressure exceeding the design limit weakening a seal
Required tools
- Combustible gas detector calibrated for hydrogen
- Seal oil system instrumentation
- DCS hydrogen purity and makeup rate trend
Safety first
- Hydrogen is flammable from 4% to 75% in air. If a fixed detector alarm sounds, evacuate non-essential personnel and eliminate ignition sources.
- Never vent hydrogen directly to atmosphere inside a confined space or near ignition sources.
- Purging procedures require trained personnel and must follow the OEM's step-by-step sequence.
Procedure
- 1
Note the current hydrogen purity and makeup rate from the control system. A purity below 95% or a makeup rate more than twice the baseline points to an active leak.
Warning: Hydrogen is flammable in air at 4-75% concentration. If a hydrogen detector alarm activates, do not create sparks or open electrical enclosures in the area. Follow your site hydrogen emergency procedure. - 2
Check the shaft seal oil differential pressure regulator to confirm the oil-to-hydrogen pressure differential is within specification. Low differential allows hydrogen to bypass the seal.
- 3
Inspect the seal oil detraining tank for excess hydrogen bubbling, which confirms the seals are allowing gas migration.
- 4
Survey the generator exterior flanges and terminal box covers with a combustible gas detector, moving slowly across each joint.[1]
- 5
If the leak is confirmed at a flange, the generator must be taken offline and the hydrogen purged to CO2 or nitrogen before the flange can be re-gasketed.
Warning: Only trained personnel may purge hydrogen from a generator. Follow the OEM purging procedure. Never purge directly to air without CO2 or nitrogen pre-fill. - 6
Contact the OEM service team if the leak is large or cannot be located from the exterior.
- 7
After repairs, perform a hydrogen leak test at normal operating pressure before returning to service.
Sources
GE GE Gen6 / Gen8 Generator (Large) general technical documentation, GE
Hydrogen-cooled generator operation and safety, general power generation references (general)
More guides for GE GE Gen6 / Gen8
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How to diagnose high stator winding temperature on a GE Gen6 / Gen8 generator
Elevated stator winding temperature with normal load usually means reduced cooling water flow or a blocked cooling passage. Check cooling water flow rate, inlet temperature, and compare RTD readings across all stator slots.
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