Transformers are either installed
indoors or outdoors. If two transformers are installed side-by-side, they shall
be separated by fire-separation walls. Fire separation walls are deemed to be
adequate even if oil capacity of individual transformers does not exceed 2000
litres, and total capacity of all transformers installed side by side exceeds
2000 litresNote 1. Ventilation is the most important thing to
be ensured in indoor installations. The area required for ventilation is also specified
as 2 m2 for outlet and 1 m2 for inlet per 1000 kVA of
transformer capacityNote 2. This area is required for natural
ventilation. If that much space is not physically available, fans may be used.
Vertical Clearance
Minimum clearance between the highest
point of the conservator tank to the ceiling of the transformer room should be
sufficient to remove the mounting on the transformer like the conservator.
However, this clearance should not be less than 0.5 m Note 3.
Horizontal Clearance
Transformers shall be kept well
away from walls. The minimum recommended spacing between the walls and
transformer is shown in Fig 1 below.
 |
| Fig 1: Minimum horizontal clearances for transformers |
The wall indicated in the figure
can also be fire separation wall. As such, there is no separate requirement for
clearance from fire separation wall.
When fire safety is also taken
into the picture, some more spatial clearances are to be observed. If
transformer oil capacity is more than 2000 litres, the building housing the
oil-filled transformer shall be separated by a distance of not less than 6 m
from all other buildings Note 4. If however, a building is
existing within 6 m, there shall not be any door or window opening in the
substation or the adjacent building. Again, if such communication also exists,
the substation shall be segregated by separating walls of 355 mm thick brick
wall or 230 mm thick RCC, carried up to roof level. Doors, if any, shall be
single fireproof with 2 h rating.
In the Code of Practice for Fire
Safety: Electrical Installations (IS 1646), the minimum clearance specified is
not in agreement with Code of Practice for Installation of Transformers (IS
10028 Part 2) when compared with Fig 1 reproduced from the latter standard.
This specifies a minimum clearance of 750 mm (0.75 m) between the transformer or
other apparatus and enclosing or separating walls Note 5. As
is usual in the case of conflicts among provisions in standards, we may take
the more stringent requirement of the two, which is, 1.25 m for transformers
with enclosing walls on all four sides.
No mention of spatial clearances
for transformers was found in the Indian Electricity Rules, 1956 and the
Central Electricity Authority (Measures Relating to Safety and Electric Supply)
Regulations, 2010.
American regulations seem to have
included clear instructions on clearances as shown in this excellent article (Safety Clearance Recommendations for Transformer) on
the Electrical Engineering Portal.
References
- Code of Practice for Selection, Installation and Maintenance of Transformers, Part 2 Installation, IS 10028 (Part 2) – 1981, Reaffirmed 2001.
- Code of Practice for Fire Safety of Buildings: Electrical Installations (Second Revision), IS 1646 – 1997, Reaffirmed 2002
- Indian Electricity Rules, 1956
- Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010
Notes:
- Clause 3.6.2 of IS 10028 Part 2 – 1981
- Clause 7.3.1.1, ibid
- Clause 7.3.1.5, ibid
- Clause 7.1 of IS 1646 – 1997
- Clause 7.4, ibid
