Why must the cooling water pressure not be higher than the hydrogen pressure, and why must the water temperature be higher than the hydrogen temperature?

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Why must the pressure of the cooling water in a generator not be higher than the hydrogen pressure? If the cooling water pressure is higher than that of the hydrogen, then in the event of a leak in the cooling water system within the generator, water will flow into the generator, causing the stator to become grounded and posing a threat to the safe operation of the generator. Therefore, during operation, the pressure of the cooling water for the generator should be kept below the hydrogen pressure by a certain amount. What if the hydrogen pressure is high and it leaks into the water? Since the hydrogen pressure is higher than that of the chilled water, the chilled water may carry some of the leaked hydrogen during operation, which will gradually accumulate in the chilled water tank as part of the water circulation. Therefore, the chilled water tank needs to be filled with nitrogen at a certain pressure. Since hydrogen has a lower density than nitrogen, it accumulates at the top of the chilled water tank. When the amount of hydrogen accumulated exceeds the operating pressure of the tank’s exhaust safety valve, this valve activates – it also has a function for measuring the amount of gas exhausted, which can be used to calculate the hydrogen leakage rate – thereby expelling the excess hydrogen outside the facility and ensuring that the hydrogen concentration inside the chilled water tank remains at a safe level. Why cannot the temperature of the cooling water be too high or too low? The main function of the cooling water system is to ensure that the cooling water (pure water) flows continuously through the stator coils, thereby removing the heat generated in those coils due to losses. This helps to keep the temperature rise of the stator coils within the limits specified for the proper operation of the generator. At the same time, the system must also control parameters such as the pressure, temperature, flow rate, and conductivity of the cooling water entering the stator coils, to ensure that their operational parameters meet the relevant specifications. The temperature range of the coolant for the generator coils is 40–50°C. An automatic adjustment device is installed to regulate the inlet water temperature, ensuring that the fluctuation range of the cooling water temperature remains within 2°C. The water temperature at the coil outlet must not exceed 85°C. If the cooling water temperature is too low, it can cause the hydrogen inside the generator to cool down and form condensation, thereby affecting the generator’s insulation properties. If the temperature is too high, it will overheat the stator windings of the generator; in severe cases, this can trigger a shutdown protection mechanism, resulting in a shutdown or a reduction in the load.