Turbogenerators

Safety Equipment for Hydrogen Operation

Safety Instructions

1 General J During normal operation practically no hydrogen can enter

The use of hydrogen as coolant in generators requires spe- the turbine system via the loop seal together with the
cial safety equipment to effectively prevent the occurrence of drained seal oil because the hydrogen is degassed from the
hazardous operating conditions which could pose a danger to seal oil in the seal oil storage tank.
the operating personnel and the plant. J In the event of loss of the seal oil supply system, the loop
This section details the safety precautions for generators. seal prevents the hydrogen from flowing into the partially
The required measuring and alarm systems are detailed in a filled oil drain pipes and thus from entering the turbine sy-
different section (see Section 2.1--8400 Measuring and stem. To limit the hazard caused by such a fault in terms of
Supervisory Equipment). time, the fast hydrogen depressurization system (if pro-
vided) is tripped automatically or the fire protection valve
2 Uncontrolled Hydrogen Losses must be opened manually.
The small leaks which can develop during operation can
result in a continuous escape of hydrogen. Provided the total 4 Permanent Ventilation of Seal Oil Storage Tank
hydrogen losses due to such leaks do not exceed 18 m3 (at The seal oil storage tank is designed as a permanently
standard temperature (0_C) and pressure (1.013 bar) as per ventilated vessel and is connected to the bearing vapor
DIN 1343) over a 24-hour period, it is not necessary to exhauster. The exhauster creates a slight vacuum in the seal
implement restrictions in terms of generator operation. See oil storage tank so that the hydrogen can degas from the seal
also DIN EN 60034, Part 3. oil. After a specified holding time, the degassed oil is routed to
If the gas losses should be so high that the rated hydrogen the turbine oil tank (which also receives the bearing oil) via a
pressure cannot be maintained, the so-called fire protection loop seal.
valve and, if installed, the fast hydrogen depressurization The permanent ventilation of the seal oil storage tank pre-
system should be tripped (cf. Section 2.3--9640 Gas Pressure vents the formation of explosive hydrogen-air mixtures even
and Volume Flow Rates). The turbine trip is activated upon under faulted conditions when hydrogen degasses from the
tripping of the fire protection valve and/or the fast hydrogen de- oil.
pressurization system. 5 Hydrogen Bottle Supply
Following activation of the fast depressurization system To avoid any undue hazard to the plant by the hydrogen
(comprising two solenoid valves in the vent gas system plus supplies, the volume of hydrogen that can be stored inside the
the fire protection valve) the generator hydrogen pressure is turbine buildings is limited to 80 m 3 (s.t.p.). Only two hydrogen
reduced to near-atmospheric pressure within 5 to 10 minutes. bottles may be opened at any one time during normal opera-
Depressurization via the fire protection valve alone is slightly tion (this does not apply to gas filling).
slower.
6 Prevention of Formation of Explosive
3 Removal of Hydrogen Pockets Loop Seal Gas Mixtures in Turbine Building
Downstream of Seal Oil Storage Tank Care should be taken to ensure that a sufficient air change
Special precautions are taken with regard to faults affecting rate is maintained at locations of potential hydrogen leaks. This
the seal oil supply. Because the shaft sealing effect breaks includes the hydrogen unit, the gas dryer, the vent gas system
down in the event of a loss of the seal oil system hydrogen can and the area underneath the generator and the foundation
flow into the bearing compartments. This hydrogen is plate. In these areas, it must be ensured that the air movement
extracted from the compartment by exhausters and vented to is perceivable (i.e. air velocities of > 0.1 m/s) in order to reliably
the environs. Under normal operating conditions, the prevent the formation of explosive hydrogen / air mixture and
exhauster creates a slight vacuum which prevents oil vapor to achieve the specified air change rate.
from escaping from the bearing compartments along the shaft. The air velocity should be measured with an anemometer.
Exhauster operation is monitored by a pressure transmitter, In cases where the specified air velocity cannot be
and if one exhauster should fail, a standby exhauster is achieved in critical locations, special ventilation measures
automatically started up. must be implemented or fans installed to ensure reliable
To prevent any hydrogen which enters the bearing mixing of the air (cf. DIN EN 60034, Part 3).
compartment from escaping via the oil drain pipes, the oil is
7 Generator Safety Zone
returned to the turbine oil tank via the seal oil storage tank and
A safety zone must be specified around the generator.
a loop seal. The loop seal is permanently filled with oil to
Within this safety zone, the performance of spark-inducing
prevent the escape of gas. The loop is designed to withstand
activities or use of naked lights is prohibited. The safety zone
transient pressure surges.
should be clearly marked with barriers (color code on floor,
The above measures have the following effects:
signs or tape). The safety zone should be 3 to 5 meters in
J The bearing compartments and oil drain pipes are perma- width. The same applies for the hydrogen unit, the hydrogen
nently ventilated and are thus not rated as explosive spaces bottle rack, the liquid level detector rack, the gas dryer and the
during normal operation. vent gas lines on the turbine building roof.

MKG
Siemens AG MKQ &MDB 2.1--8310--0004
Energy Sector MKW 0908E