COMPRESSED-AIR-FOAM (CAF) SYSTEM FOR FIRE PROTECTION OF POWER TRANSFORMERS
by
Andrew Kim* and George Crampton
Fire Research Program, Bldg. M-59,
Institute for Research in Construction,
National Research Council of Canada
1200 Montreal Road,
Ottawa, Ontario, K1A 0R6,
Canada
e-mail: andrew.kim@nrc-cnrc.gc.ca
* Author to whom correspondence should be addressed: E-mail; andrew.kim@nrc-cnrc.gc.ca, Phone #; (613) 993-9555, Fax #; (613) 954-0483
INTRODUCTION
Power transformers play an important role in making communities function by distributing the power. Power transformers deal with high voltage electric power and there is a strong possibility of accidental fire incidents in the power transformer. Because of the high possibility of fire occurrence and the important role they play in the maintenance of normal life in the community, the power transformers must have a proper fire protection system in place to provide the best fire protection.
Current fire protection systems for power transformers using sprinklers require a large quantity of water, which may cause a problem to their electrical function as well as creating water damage and environmental effects. Also, clean-up after fire suppression is another problem. Power transformers contain hazardous materials, and any run-off water from the fire suppression activities has to be collected. It is a costly proposition to provide infrastructure to contain the run-off water resulting from the fire suppression of a power transformer. Another fire protection approach is to use an air-aspirated foam system. However, current air-aspirated foam systems produce poor quality foam, therefore a large quantity of foam is needed to provide proper fire protection to the power transformers. This again creates a clean-up problem afterwards, delays the re-start of the power transformers and prolongs the power shutdown to the community.
The National Research Council of Canada (NRC) has developed a means of producing Compressed-Air-Foam (CAF) in a fixed pipe system. This system provides superior quality foam with uniform distribution and high momentum. In previous studies, NRC has proven by full-scale tests that CAF has superior fire suppression performance compared to current foam or sprinkler systems. Therefore, CAF may be an ideal solution in providing fire protection forpower transformers, with its superior fire suppression performance and low water requirement, thus minimizing the clean-up problem.
Recently, a study was carried out to develop a CAF distribution system and to evaluate the fire suppression capability of the CAF system for the protection of power transformers. This paper describes the experimental facility, including the power transformer mock-up and instrumentation, and presents experimental results of the fire suppression capability of the CAF system for power transformer protection.
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CONCLUSION
CAF systems with 3 or 4 TAR nozzles and with 2 GDR nozzles were developed to protect power transformers. A series of full-scale fire tests was conducted using a test mock-up, which represents a one half section of a power transformer, to measure the effectiveness of water deluge and CAF systems in extinguishing a large simulated power transformer fire, using Class A and Class B foam concentrates.
The test results clearly showed that the CAF system, either with 2 large GDR nozzles or with 3 or 4 small TAR nozzles, performed much better than the water deluge system with 21 sprinkler heads. The CAF system with 3 TAR nozzles using 1% Class A foam concentrate extinguished the test fire in 4 min 2 s, which is almost the same as the results of the water deluge system. However, the 3 TAR CAF system used less than 8% of the total water flow rate of the water deluge system.
The CAF system with 2 GDR nozzles using 2% Class B foam concentrate extinguished the test fire in 1 min 58 s, which is almost one half of the extinguishment time of the water deluge system. And, the water usage was less than 18% of the total flow rate of the water deluge system. The CAF system with 8 TAR nozzles using 2% Class B foam concentrate extinguished the test fire in 1 min 29 s, with far less water requirement than the water deluge system.
The study clearly shows that a CAF system can provide necessary fire protection for power transformers, more effectively with much less water requirement, compared to a traditional water deluge system.
