OTHER COOLING SYSTEMS
The hydrogen is cooled by passing it through a water-cooled heat exchanger mounted in the casing. The heat exchanger has nonferrous tubes. The heat exchangers have a double- pass water circulation to the inlet and outlet water connections at the same end. Demineralized water is used for these coolers.
Lake water is not used for these coolers due to the danger of corrosion. The hydrogen is maintained at a higher pressure than the cooling water in the heat exchanger. In the event of a leak, hydrogen will leak into the water (water ingress into the hydrogen can have seri- ous consequences). In modern design, the water circuit has hydrogen detectors (Fig. 13.37). The hydrogen coolers have some redundancy. It is possible to operate with one hydrogen cooler isolated. The loss of cooling water is detected by an increase in the cooling temper- ature. The rapid increase in hydrogen temperature will cause the unit to trip. The rotating exciters and slip ring/brush gear or rotating rectifier chambers have air cooling systems. A closed air circuit with a water-cooled heat exchanger is used for the rotating exciter. Open air ventilation is normally used for the slip rings.