Fire fighting system in power station

The fire fighting system of a power station detects a fire early, raises an alarm and puts it out quickly, so that costly equipment (transformers, generators, cable galleries, oil stores) is saved and people are safe.

Main fire risks

• Transformer and switchgear insulating oil
• Generator windings (insulation, and hydrogen in large units)
• Cable trenches and galleries
• Fuel oil and coal stores, battery rooms

Components of the system

 +--------+   +-------------+   +-----------------+
 | Fire   |-->| Fire alarm  |-->| Alarm (bells,   |
 |detector|   | control pnl |   | lamps) + trip   |
 +--------+   +------+------+   +-----------------+
                     | opens deluge valve
 +-------+  +-------+v +-------+   +-----------+
 | Water |->| Pumps |->|Deluge |-->| Spray     |
 | tank  |  |(el+DG)|  | valve |   | nozzles   |
 +-------+  +-------+  +-------+   | (on xfmr) |
                                   +-----------+

1. Detection: smoke, heat (rate-of-rise) and flame detectors; for transformers, quartz bulb or linear heat detectors placed around the tank.
2. Alarm panel: receives detector signals, sounds the alarm, shows the zone, trips the equipment and starts the extinguishing system.
3. Extinguishing systems:
   • Hydrant system: a ring main of pipes with hydrant points and hoses, kept pressurised by a jockey pump, with a main electric pump and a standby diesel pump.
   • Water spray (deluge) / mulsifire system: for transformers; a high-velocity water spray forms an emulsion on the oil surface, cools it and cuts off oxygen.
   • CO$_2$ flooding system: for generators, control rooms and cable vaults; CO$_2$ cylinders discharge automatically and dilute the oxygen. Used where water would damage equipment.
   • Foam system: for oil tanks and fuel stores.
   • Portable extinguishers: CO$_2$, dry chemical powder and foam types near equipment.
4. Passive measures: oil soak pits filled with gravel under transformers, fire walls between transformers, fire-resistant cable coating and fire barriers.

Requirements

• Automatic operation with manual back-up.
• A reliable, separate water supply and a standby diesel pump.
• Regular testing of detectors, pumps and cylinders.