There are three distinct processes in monitoring hydrogen-cooled turbo generators: normal operation, filling and emptying. The measuring task entails preventing a gas mixture of hydrogen and air outside the specified limits, or detecting the risk of this happening in good time, as well as monitoring the hydrogen purity.
During normal operation, the purity of the generator cooling gas is monitored. If the purity falls below a specific limit (e.g. < 95 % H2), a message is output. The monitored range is 80 to 100 % H2 in air.
Filling the generator is a two-stage procedure: first, the air in the generator is replaced by inert gas (argon or CO2), and then this is replaced by hydrogen. During this, the concentration trends of the gases are measured and the replacement processes monitored. To prevent explosive mixtures from being formed, it is necessary to monitor the measuring range of 0 to 100 % inert gas in air in the first step and 0 to 100 % H2 in inert gas in the second step.
The procedure is performed in reverse when emptying the generator: The hydrogen is first replaced with inert gas and the generator is then filled with air. The measuring tasks remain unchanged in this case. Here it is necessary to monitor the measuring ranges of 0 to 100 % H2 in inert gas first, and then 0 to 100 % inert gas in air.