Transformer Clearance (Indoor and Outdoor) and Fire Protection-PART-2

TRANSFORMER CLEARANCE (INDOOR AND OUTDOOR) AND FIRE PROTECTION-PART-2

FIRE PROTECTION FOR POWER PLANTS (NFPA 850)

LOCATION

TYPE OF TRANSFORMER

DETAILS

OUTDOOR

Oil-insulated outdoor type transformer containing 1890 liters or more of oil It is strongly recommended that any is separated from nearby structures by a 2-hour–rated firewall Wherever a firewall is installed between transformers , it should extend at least 1 ft (0.31 m) above the top of the transformer shell and oil tank and at least 2 ft (0.61 m) beyond the width of the transformer and cooling radiators.

INDOOR

Dry type Transformer Dry-type transformers are strongly preferred for use inside buildings. oil-insulated transformer In case however, an oil-insulated transformer is installed indoors, then if its oil content exceeds 379 Liters, then it should be separated from nearby areas by a fire barrier of 3-hour fire resistance rating. In case an automatic fire extinguishment system is installed, then it is allowed that the fire resistance rating of the fire barrier is reduced to 1 hour.

NFPA 850 – TABLE 6.1.4.3-OUTDOOR OIL-INSULATED TRANSFORMER SEPARATION CRITERIA

Transformer Oil Capacity Minimum (Line-of-Sight) Separation Without Firewall

<1893 Liter

1.5 Meter 1893 liter to 18925 liter

7.5 Meter

18925 liter

15 Meter

4.2-SUBSTATIONS AND SWITCH ROOMS (NATIONAL BUILDING CODE 2016)

Oil Filled Transformer at Basement Level (Indoor Type)

Substations with oil-filled equipment/ apparatus Transformers and high voltage panels shall be either located in open or in a utility building. They shall not be located in any floor other than the ground floor or the first basement of a utility building. They shall not be located below first basement Slab (On Second Basement) of utility building. They shall have direct access from outside the building for operation and maintenance of the equipment. In respect of all oil type transformers located at basement, a kerb (sill) of a suitable height shall be provided at the entrance in order to prevent the flow of oil from a ruptured transformer into other parts of the basement in the event of the possibility of oil spillage from the transformer on its failure.

Oil Filled Transformer/ Sub Station (Outdoor Type)

The substation or oil-filled transformer is located shall be separated from the adjoining buildings including the main building by at least 6 Meter clear distance to allow passage of fire tender between the substation/utility building and adjoining building/main building. There shall be no interconnecting basement with the main building underneath the oil-filled transformers. Provisions for oil drainage to a point at a lower level and separated by adequate fire barrier shall be provided. If there is a floor directly below the ground floor level or first basement where the oil-filled transformers and oil-filled circuit breakers are placed, then they shall be separated by a fire barrier of appropriate fire rating as per Part 4 Fire and Life Safety of the Code and proper oil drainage system shall be provided to avoid possible leakage of oil into the lower floor. Substation equipment (exceeding oil capacity of 2 000 liter) in utility building shall have fire rated baffle walls of 240 min rating constructed between such equipment, raised to at least 600 mm above the height of the equipment (including height of oil conservators) and exceeding 300 mm on each side of the equipment All transformers where capacity exceeds 10 MVA shall be protected by high velocity water spray systems or nitrogen injection system.

Oil Filled Transformer (9000 Liter) (Indoor / Outdoor Type)

Provisions shall be made for suitable oil soak-pit, and where use of more than 9 000 liter of oil in any one oil tank, receptacle or chamber is involved, provision shall be made for the draining away or removal of any oil which may leak or escape from the tank, receptacle or chamber containing the same. Special precautions shall be taken to prevent the spread of any fire resulting from the ignition of the oil from any cause and adequate provision shall be made for extinguishing any fire which may occur.

Dry-Type Transformer Within Multi-Storied Building

Dry-type installation In case electric substation has to be located within the main multistoried building itself for unavoidable reasons, it shall be a dry-type installation with very little combustible material, such as, a dry type transformer with vacuum (or SF6) breakers as HT switchgear and ACB or MCCB as medium voltage (MV) switchgear. Such substations shall be located on the ground level or on first basement, and shall have direct access from the outside of the building for operation and maintenance of the equipment. Exceptionally, in case of functional buildings, such as air traffic control towers, data center’s and buildings of height more than 100 m having high electrical load requi…