Transformer Clearance (Indoor and Outdoor) and Fire Protection-PART-1

April 29, 2023 3 Comments

IEC 61936-1-Table 3 – Guide values for Outdoor Transformer Clearances
Transformer type Liquid volume Clearance to other transformers or non-combustible building surface Clearance to combustible building surface
Oil insulated transformers (O) 1000 Liter to 2000 Liter 3 Meter 7.6 Meter
2000 Litre to 20000 Litre 5 Meter 10 Meter
20000 Litre to 45000 Litre 10 Meter 20 Meter
More than 45000 Liter 15.2 Meter 30.5 Meter
Less flammable liquid insulated transformers (K)
without enhanced protection		 1000 Liter to 3800 Liter 1.5 Meter 7.6 Meter
More than 3800 Liter 4.6 Meter 15.2 Meter
Less flammable liquid insulated transformers (K) with enhanced protection Clearance to building surface or adjacent transformers
 Horizonal =0.9 Meter
 Vertical=1.5 Meter
Dry-type transformers (A) Fire behavior’s class Clearance G to building surface or adjacent transformers
Horizonal vertical
F0 1.5 Meter 3 Meter
F1/F2 NILL NILL
Note: If automatically activated fire extinguishing equipment is installed, the clearance can be reduced
Note: If it is not possible to allow for adequate clearance as indicated in table 3, fire-resistant separating walls with the following dimensions shall be provided:
Between transformers (see figure) separating walls. For example EI 60 in accordance
(i) Height: top of the expansion chamber (if any), otherwise the top of the transformer tank;
(ii) Length: width or length of the sump (in the case of a dry-type transformer, the width or length of the transformer, depending upon the direction of the transformer);
Note: Where transformers with a liquid volume below 1000 Litre are installed near combustible walls, special fire precautions may be necessary depending on the nature and the use of the building

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IEC 61936-1-Table 4 – Minimum Requirements for the Installation of Indoor Transformers
Transformer type Liquid volume Safeguard
Oil insulated transformers (O) <=1000 Liter EI 60 respectively REI 60
More than 1000 Liter EI 90 respectively REI 90 or EI 60 respectively REI 60 and automatic sprinkler protection
Less flammable liquid insulated transformers (K) without enhanced protection EI 60 respectively REI 60 or automatic sprinkler protection
Less flammable liquid insulated transformers (K) with enhanced protection <= 10 MVA and Um <= 38 kV EI 60 respectively REI 60 or separation distances 1.5 Meter horizontally and 3.0 Meter vertically
Dry-type transformers (A) Fire behavior’s class  
F0 EI 60 respectively REI 60 or separation distances 0.9 Meter horizontally and 1.5 Meter vertically
F1/F2  Non-combustible walls
Note: Between transformers and buildings separating walls shall be provided. For example EI 60; if additional fire separating wall is not provided, fire rating of the building wall should be increased, for example REI 90

IS 3034: 1993
SIZE OF TRANSFORMER FIRE PROTECTION
<=10 MVA or Oil filled Transformers with oil capacity of <=2 000 Liters No fixed fire protection equipment (such as high velocity spray) is required
>10 MVA or Oil filled Transformers with oil capacity of >2 000 Litres High velocity water spray system, shall be provided. This system shall be separately mounted and designed to take into account the possibility of a transformer explosion.
The water spray deluge valve house shall be located outside the transformer fire zones and protected from radiant heat and other fire effects. The actuation of this system shall be automatic but manual operating valves shall also be provided
The positioning of the nozzles should be such to protect all surfaces of the transformer and to give discharge rate for the system not less than 10 Ipm/m of the area to be protected.
The automatic high velocity water spray shall be of pre-active with quartzoid bulbs.
Distance between two transformers is less than 15 Meter apart or where the oil capacity > 2000 Liters Fire barriers walls shall be provided between transformers.
 Transformers having an aggregate oil capacity exceeding 2000 liters but an individual oil capacity of fewer than 5000 liters Separating walls shall not be necessary.
If the distance between transformers and other apparatus is more than 6 Meter
If the transformers are protected by an approved high-velocity water spray system

IS 3034: 1993-Table 1 Clearance from Water Spray Equipment to Live Un Attended Electrical Components
Nominal Line Voltage Design BIL Minimum Clearance
up to 15KV 110KV 178MM
23KV 150KV 254MM
34.5KV 200KV 330MM
46KV 250KV 432MM
69KV 350KV 635MM
115KV 550KV 940MM
138KV 650KV 1118MM
161KV 750KV 1321MM
196 TO 230KV 900-1050KV 1600-1930MM
287 TO 380KV 1175-1550KV 2210-3048MM
500KV 1675-1880KV 3327-3607MM
500 TO 700KV 1925 -2300KV 3886-4674MM

Section 64 in The Indian Electricity Rules, 1956
2000 liters of oil installed, whether indoor or out-doors The baffle walls of 4-hour fire rating shall be provided between the
apparatus in the following cases
(i) Single phase banks in the switch-yards of generating stations and substations.
(ii) On the consumer premises
(iii) Where adequate clearance between the units is not available
Provisions shall be made for suitable oil soak pit and where use of more
than 9000 liters 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 tanks receptacles or chambers 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. Spare oil shall not be stored in an such sub-station or switch station
Where it is necessary to locate the Transformer /Sub-Station in the basement following measures shall be taken The room shall necessarily be in the first basement at the periphery of the basement.
The entrances to the room shall be provided with fire resisting doors of 2 hours fire rating. A curb (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. Direct access to the transformer room shall be provided from outside.
The transformer shall be protected by an automatic high velocity water
spray system or by carbon dioxide or BCF(Bromochlorodifeuromethane) or  BTM (Bromotrifluromethane) fixed installation system.
Oil filled transformers installed indoors shall not be on any floor above the ground or below the first basement.
A sub-station or a switch station with apparatus having more than 2000
liters of oil shall not be located in the basement where proper oil draining arrangement cannot be provided.

CEA Technical Standards for Construction of Electrical Plants and Electric Lines) Regulations, 2010. Clause 54
>=33 kV voltage Transformers shall be separated from one another by a firewall.

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