16 September 2012

Safety Clearance for Transformer



 Clearance from Outdoor Liquid Insulated Transformers to Buildings (NEC):

LiquidLiquid Volume (m3)Fire Resistant WallNon-Combustible WallCombustible WallVertical Distance
Less FlammableNA0.9 Meter0.9 Meter0.9 Meter0.9 Meter
<38 m3="m3" span="span">1.5 Meter1.5 Meter7.6 Meter7.6 Meter
>38 m34.6 Meter4.6 Meter15.2 Meter15.2 Meter
Mineral Oil<1 .9=".9" m3="m3" span="span">1.5 Meter4.6 Meter7.6 Meter7.6 Meter
1.9 m3 to 19 m34.6 Meter7.6 Meter15.2 Meter15.2 Meter
> 19 m37.6 Meter15.2 Meter30.5 Meter30.5 Meter

 Clearance between Two Outdoor Liquid Insulated Transformers (NEC):

LiquidLiquid Volume (m3)Distance
Less FlammableNA0.9 Meter
<38 m3="m3" span="span">1.5 Meter
>38 m37.6 Meter
Mineral Oil<1 .9=".9" m3="m3" span="span">1.5 Meter
1.9 m3 to 19 m37.6 Meter
> 19 m315.2 Meter

 Dry Type Transformer in Indoor Installation (NES 420.21):

Voltage
Distance  (min)
Up to 112.5 KVA300 mm (12 in.) from combustible material unless separated from the combustible material by a heat-insulated barrier.
Above 112.5 KVAInstalled in a transformer room of fire-resistant construction.
Above 112.5 KVA with Class 155 Insulationseparated from  a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

 Dry Type Transformer in Outdoor Installation (NES 420.22):

Voltage
Distance  (min)
Above 112.5 KVA with Class 155 Insulationseparated from  a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

 Non Flammable Liquid-Insulated Transformer in Indoor Installation (NES 420.21):

Voltage
Distance  (min)
Over 35KVInstalled indoors Vault (Having liquid confinement area and a pressure-relief vent for absorbing any gases generated by arcing inside the tank, the pressure-relief vent shall be connected to a chimney or flue that will carry such gases to an environmentally safe area
Above 112.5 KVAInstalled in a transformer room of fire-resistant construction.
Above 112.5 KVA (Class 155 Insulation)separated from  a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

 Oil Insulated Transformer in Indoor Installation (NES 420.25):

Voltage
Distance  (min)
Up to 112.5 KVA
Installed indoors Vault (With construction of reinforced concrete that is not less than 100 mm (4 in.) thick.
Up to 10 KVA & Up to 600V
Vault shall not be required if suitable arrangements are made to prevent a transformer oil fire from igniting
Up to 75 KVA & Up to 600V
Vault shall not be required if where the surroundingStructure is classified as fire-resistant construction.
Furnace transformers (Up to 75 kVA)Installed without a vault in a building or room of fire resistant construction

 Transformer Clearance from Building (IEEE Stand):

Transformer
Distance from Building  (min)
Up to 75 KVA
3.0 Meter
75 KVA to 333 KVA
6.0 Meter
More than 333 KVA
9.0 Meter

 Transformer Clearance Specifications (Stand: Georgia Power Company):

Description of Clearance
Distance  (min)
Clearance in front of the transformer
3.0 Meter
Between Two pad mounted transformers (including Cooling fin)
2.1  Meter
Between Transformer and Trees, shrubs, vegetation( for unrestricted natural cooling )
3.0 Meter
The edge of the concrete transformer pad to nearest the building
4.2 Meter
The edge of the concrete transformer pad to nearest  building wall, windows, or other openings
3.0 Meter
Clearance from the transformer to edge of (or Canopy) building (3 or less stories)
3.0 Meter
Clearance in front of the transformer doors and on the left side of the transformer, looking at it from the front. (For operation of protective and switching devices on the unit.)
3.0 Meter
Gas service meter relief vents.
0.9 Meter
Fire sprinkler values, standpipes and fire hydrants
1.8 Meter
The water’s edge of a swimming pool or any body of water.
4.5 Meter
Facilities used to dispense hazardous liquids or gases
6.0 Meter
Facilities used to store hazardous liquids or gases
3.0 Meter
Clear vehicle passageway at all times, immediately adjacent of Transformer
3.6 Meter
Fire safety clearances can be reduced by building a suitable masonry fire barrier wall (2.7 Meter wide and 4.5 Meter Tall) 0.9 Meter from the back or side of the Pad Mounted Transformer  to the side of the combustible wall

Front of the transformer must face away from the building.

Clearance of Transformer-Cable-Overhead Line (Stand: Georgia Power Company):

Description of Clearance
Horizontal Distance (mm)
to pad-mounted transformers
to buried HV cable
to overhead HV Line
Fuel tanks
7.5 Meter
1.5 Meter
7.5 Meter
Granaries
6.0 Meter
0.6 Meter
15 Meter
Homes
6.0 Meter
0.6 Meter
15 Meter
Barns, sheds, garages
6.0 Meter
0.6 Meter
15 Meter
Water wells
1.5 Meter
1.5 Meter
15 Meter
Antennas
3.0 Meter
0.6 Meter
Height of Antenna + 3.0 Meter

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