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

May 23, 2023 2 Comments

 

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 requirement, dry-type installations/substations may also be provided at upper level. This measure will decrease the current flow and short-circuit rating at various points, thereby reducing vulnerability to fire. In such cases, a base substation shall be located at ground floor/first basement to cater to the main MV/LV panel which feeds life and safety services loads
The base substation shall be located in such a way to provide direct access to the firemen in case of any emergency. The power supply control to any substation or transformer located at upper floors shall be from the base substation so that in case of fire, the electrical supply can be easily disconnected to avoid additional losses.
Transformers located inside a building shall be of dry type and all substation/switch room walls, ceiling, floor, opening including doors shall have a fire resistance rating of 120 min. Access to the substation shall be provided from the nearest fire exit/exit staircase for the purpose of electrical isolation.

Two Transformer (Dry type or transformers with oil quantity less than 2000 liters )

In case of two transformers (Dry type or transformers with oil quantity less than 2000 liters ) located next to each other without intermittent wall, the distance between the two shall be minimum 1500 mm for 11 kV, minimum 2000 mm for 22 kV and minimum 2500 mm for 33 kV. Beyond 33 kV, two transformers shall be separated by a baffle wall 4 h fire rating.
If dry type transformer is used, it may be located adjacent to medium voltage switchgear in the form of unit type substation. In such a case, no separate room or fire barrier for the transformer is required either between transformers or between  transformer  and  the  switchgear, thereby decreasing the room space requirement.
Layout of equipment should take care of the need that any one piece of equipment or sub assembly can be taken out of service and out of the installed location, while keeping the remaining system in service. Working space for access for maintenance of equipment, while keeping an adjoining section of the substation live to maintain  power supply to essential loads,

CSS

 In case of compact substation design and location of the substation shall ensure safety of the people around the compact substation installed along walkways,  playgrounds,  etc.
Compact substation with incomer voltage of 12 kV or less, when located in open areas shall have fencing  or  barrier  (of  any metal  based protection, such as wire mesh or chain link, which is duly earthed) against unauthorized contact possibility around it at a minimum distance of 750 mm around it with access for maintenance from all four sides.
For incomer voltage more than 12 kV and less than 24 kV the fencing distance from substation may be 1000 mm minimum. In case of more than 24 kV incomer, the distance may be further increased accordingly. The fencing design should take care  of  the  servicing  and maintenance requirements of the substation equipment.

 

IS 1646
Type of Transformer Description

Each oil-filled apparatus, such as transformer, bank of static condensers, including high tension circuit breakers, switch and main distribution boards, having an individual or aggregate oil capacity of 2000 liters (Indoor)

 Transformer shall also be segregated from all other apparatus by 355 mm thick fire resisting brick wall or 230 mm thick RCC. The separating wall shall be carried right up to the roof level unless the roof is more than 3 Meter above the highest point of the equipment, in which case the wall shall be carried up to a height at least 600mm
(i) This provision need not be applied to furnace and rectifier transformers as also to transformer of testing apparatus or other equipment of which the transformer is an integral part, whether they are oil-filled or not.
(ii) The requirements given under this rule, however, do not apply to dty type transformers, or transformers having sulphur hexafluoride, non-flammable coolants and having primary voltage not mote than 33 kV.
(iii) If the substation supplies power to fire pumps, separating walls as described above will be necessary between the various items irrespective of the oil contents.

Every oil-filled apparatus, such as transformer, static condenser, switchgear or oil circuit breaker having an individual or aggregate oil capacity of 2000 liters or more (Indoor)

  Transformer shall be housed in a locked, weather and fire resistant building and shall be properly ventilated to the outside of the building only.
(i) The building housing the oil-filled apparatus shall be separated by a distance of not less than 6 Meter from all other buildings.
(ii) If the building housing the transformer is within 6 m of the surrounding building there shall not be any door or window opening in the substation or the surrounding building.
 (iii) If the building or compartment housing oil-filled apparatus is communicating with another building or compartment, the substation shall be segregated by separating walls of 355 mm thick brick wall or 230 mm thick RCC, carried up to roof level with door openings therein protected by single fireproof doors of 2 hour rating.
(iv) Notwithstanding the above, if the substations supplies power to fire pumps, the same shall be segregated from, the adjoining building by 400 mm thick brick wall or 300 mm thick RCC wall without any door opening there in where, however, door openings are absolutely necessary, the openings shall be protected by double fire resisting doors of 2 hour rating each. If the substation is attached to a stormed structure, in addition to segregations, it will also be necessary for the substation to be provided with RCC slab roof.

Each building or compartment housing oil filled apparatus containing 2000 liters or more (Indoor)

  Transformer shall be provided with oil drains of at least 150 mm in diameter and soak pits, the latter being not less than 2.5 meter away from the substation.
Floors shall be sloped not less than 1 in 96 towards oil drains.
The soak pits shall be of sufficient capacity to take the entire oil content of the equipment and designed to provide for drainage of liquids to a safe location.
A minimum clearance of 750 mm shall be provided between the transformer or other apparatus and enclosing or separating walls.

Transformers and equipment installed outdoors, having an individual or aggregate oil content of 2 000 liters or more (Outdoor)

 Transformer shall be located in a suitably fenced and locked enclosure separated on all sides by at least 6 Meter from any building including substation.
Separating walls are necessary between transformers having an individual or aggregate oil content of 2000 liters.
There should be no door or window opening in the surrounding building, if the transformers are within 6 m thereof.
If the transformers are within 6 Meter of doors and window openings of surrounding buildings then they shall be protected by single fire proof doors and 6 mm thick wired glass in steel frames respectively.
Separating walls shall not be necessary in case of transformers having an aggregate oil capacity exceeding 2000 Liters but individual oil capacity of less than 5000 Liters if the distance between transformers and other apparatus is more than 6 Meter or if the transformers ate protected by an approved high velocity water spray system.
Where however oil capacity of individual transformer is larger than 5 000 liters separating walls shall be provided unless all equipment/building/plant are located at a clear distance of not less than the following
5000 To 20000 Liter Oil Capacity of Individual Transformer= 8Meter Clear Separating Distance
Over 20 000 Liter Oil Capacity of Individual Transformer= 15Meter Clear Separating Distance

 

IS: 1002
Indoor Transformer Transformers installed inside buildings, where the oil capacity exceeds 2 000 liters of oil, shall be provided with oil soak pits. Oil soak pits may also be made of RCC tanks.
For indoor transformers, Oil soak pits shall be provided either under the transformer or outside the transformer room.
Two or more transformers are installed side by side They shall be separated by fire-separation walls. Fire separation walls are deemed to be adequate from fire-safety point of view, even if oil capacity of individual transformers do not exceed 2 000 litres, and total capacity of all transformers installed side by side exceeds 2 000 liters.
Soak Pit The capacity of the oil soak pit shall be such that to soak the entire oil content of the transformer, it is intended for individual soak pits for each transformer ( wherever necessary) with capacity as above or a common soak pit to contain the entire oil content of the biggest of the transformers shall be adequate.

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