- Hydrant System Definition: A hydrant system is a water-based fire protection setup in thermal power plants, including components like valves, hoses, and nozzles.
- Components of a Hydrant System: Essential parts include fire water ring mains, isolation valves, hydrant valves, hose cabinets, couplings, and water monitors.
- Hydrant System Requirements: The system must maintain 3.5 Kg/cm² pressure at the farthest point, with a max velocity of 5 m/s in the main pipes.
- Spray System Working Principle: The spray system automatically detects and controls fires using deluge valves and fire detection devices.
- High Velocity Water Spray System (HVWS): The HVWS is a fire protection system with automatic detection and extinguishing features, covering critical areas like transformers and oil storage tanks.
Power Plant Fire Protection System (Part-II of III)
A fire protection system known as the hydrant system is a pressurised fire-water ring that feeds outdoor hydrants, indoor landing valves, hose cabinets and water monitors. On Indian thermal power plants that ring is usually written to TAC. This page is Part II of the three-part fire-protection series.
Flow scheme for a typical 660 MW unit (this specification):
Hydrant System
The Hydrant system on this specification is a fire-water ring main plus:
- Isolation gate valves on RCC pedestals around the protected areas.
- Hydrant valves (external/internal)
- Hose cabinets
- Couplings
- Branch pipe
- Nozzles and water monitors along with all accessories.
- Mild-steel painted hose boxes and the other TAC fittings listed for an Indian insured plant.
- Yard hydrants, hose houses or hose boxes around building perimeters. Internal hydrant hose boxes at each staircase landing (IS 3844 / NBC practice).
Fixed outdoor water monitors on this specification cover:
- ESP areas,
- Boiler house
- Tall building
- Coal stock pile area
- Bunker building
- Junction tower/transfer towers and
- Coal-conveyor spots that a yard hydrant stream cannot reach from the hydrant system.
Hydrant System Requirements
Hydrant system hydraulics on an Indian insured plant follow TAC. NFPA 14/24 use different residual-pressure and spacing rules. This specification uses:
- About 3.5 kg/cm2 residual pressure at the hydraulically remotest hydrant while the hydrant pump runs at rated flow and head (TAC / IS 3844). NFPA 14 Class I standpipes typically ask about 6.9 bar (100 psi) at the hose outlet, so do not copy 3.5 kg/cm² onto an NFPA job.
- Velocity in the hydrant main not above 5.0 m/s on this spec.
- At least two hydrants on a separate ring around the main plant.
- Outdoor hydrants about 45 m apart on this TAC sheet. Internal landing valves about 45 m apart in TG hall, mill bay and Boiler areas, and about 30 m apart on other floors. Confirm spacing against the adopted code; NFPA 24 yard hydrants are often farther apart.
- A building is treated as hydrant-protected on this sheet if a hydrant stands within 15 m of it.
- Each landing valve and external hydrant at the main plant, including the transformer yard, TG building and boiler area, has a hose box.
- Each ring main ends with an isolation valve and a blank flange at the corners for later extension.
- Booster-pump head is set for the highest remote boiler landing and pressure is proven at that elevation.
- Boiler stairs, turbine buildings, CHP transfer points, crusher house, bunker floors and auxiliary buildings get landing valves with hose boxes and hose reels.
Spray System
A water-spray system is held wet up to the deluge valves. Quartzoid bulb detectors (often written quartzite on Indian sheets) or other fire detection devices trip those valves.
This specification applies spray to transformer compounds, turbine oil systems, oil tanks, coolers and purifiers. The set includes spray pumps, pressure control, valves and strainers. Two spray types are used:
- High Velocity Water spray system (HVWS system)
- Medium Velocity Water spray system (MVWS system)
High Velocity Water Spray System (HVWS)
HVWS on an Indian insured plant is written to TAC. The set is piping, deluge valves, isolation gates, projector nozzles, quartzoid-bulb detectors and pressure switches. Heat at a detector opens the deluge valve so projectors throw a solid-cone emulsifying spray onto the oil fire. That spray cools and emulsifies the oil fire. Isolation, bunding and fire-water duration still have to be checked.
An isolation gate and a Y-strainer sit upstream and downstream of each deluge valve. A fast butterfly valve bypasses the deluge valve so an operator can open spray by hand if the automatic valve fails.
TAC asks at least 3.5 bar at the hydraulically most remote nozzle on outdoor transformers. NFPA 15 uses a density and residual-pressure calculation that may not match that figure.
Projector cones are set to overlap so the tank and radiators are covered.
HVWS on this sheet covers:
- All oil filled Generator transformers and its surrounding areas.
- Unit auxiliary transformers.
- Unit transformers.
- Station auxiliary transformers.
- Stand-by maintenance transformers.
- Bus reactors.
- CHP auxiliary transformers.
- AHP auxiliary transformers.
- Station transformers rated 10 MVA and above (this TAC sheet; smaller units follow the project fire-risk study).
- All type of oil storage tanks.
- Oil coolers and purifiers unit.
- Boiler’s burner and its surroundings.
- Turbine Lube oil storage tanks and Turbine Oil purifier.
- Clean and dirty lube oil tanks.
- Boiler Feed Pumps lube oil tanks, coolers, consoles etc.
- Turbine Oil canal pipelines in main plant.
- Fuel Oil Pressurizing and Heating Units
