Friday, April 1, 2011

Requirements of Transformer Installations in India


1. Minimum clearance between supplier's and consumer's 11 kV structures shall be 3 m. If it is 5 m or less they should be braced together both at top and middle.

2. Minimum size of RSJ poles shall be 175 x 85 mm. Channels shall be of minimum 75 x 50 mm.

3. Phase to phase and phase to earth clearances at AB switch shall be minimum 915 mm and 610 mm respectively.

4. Minimum size of 11 kV jumpers shall be Number '0' SWG copper.

5. Maximum length of unsupported 11 kV jumpers shall be 2.44 m for solid conductors and 1.5 m for stranded conductors.

6. Minimum safety working clearance of 2.6 m shall be maintained for bare conductors and live parts.

7. Lightning arrestors shall be provided between AB switch and D.O. / H.G. fuse.

8. Group control AB switch shall be provided for multiple transformer installations.

9. The minimum clearance from ground to the 11 kV bushings of the transformers shall be 2.6 m

10. AB switch operating handle shall be fixed at 1 m to 1.25 m from ground level.

11. 11 kV AB switch shall be three insulator type.

12. Fencing with a height of 2.5 m shall be provided, keeping a minimum clearance of 1.5 m from the transformer body.

13. Minimum clearance between 11 kV up and down jumpers shall be 75 cm.

14. Outdoor transformer is not permitted in corporation areas and at the premises of high-rise apartment buildings. However outdoor transformers with cable end boxes at both sides and indoor breaker/SFU at primary side may be permitted judiciously.

15. Indoor transformer is recommended for rating above 630 kVA

16. If more than one transformer, having more than 2000 litres of oil, are installed side by side, baffle walls of minimum 4 hr fire rating shall be provided in between transformers.


1. Only dry type transformers shall be installed inside residential/commercial buildings (Rule 64(2)(e)(iv)).

Oil filled transformers are permitted outside residential and commercial buildings subject to the following conditions.

(a) Only indoor type transformers are permitted in Corporation areas and at the premises of residential buildings.

(b) There shall be free access for fire engines to the transformer stations.

(c) The building in which transformer is installed shall have minimum clear distance of 1.5 m from the residential/commercial buildings.

(d) The substation building shall be of weatherproof and fire proof construction. Walls shall be of 355 mm thick brick or 230 mm thick RCC. If there is any window/door opening towards the residential/commercial building, there shall be a fire resistant wall between the substation building and residential/commercial building keeping a minimum clear distance of 1.5 m from both the buildings.

(e) Transformers may be installed outdoor, keeping a minimum distance of 6 m from commercial buildings in areas other than corporation areas.

(f) If the transformer is installed outdoor with in 6m from commercial buildings, there shall be a fire resistant wall in between the transformer and the building keeping a minimum distance of 1.5m both from the building and the transformer.

2. Only dry type transformer shall be installed in cellars and above ground floor. Indian Electricity Rules, 1956 (Rule 64(2) (f) (iii))

3. ABSF unit/VCB shall be provided at primary side. The 11 kV ABSF unit shall have CPRI test certificate and brand certification. At hospital premises breaker shall be recommended.

4. Minimum size of cable at 11 kV side shall be 150 XLPE (Aluminium). But size may be 70 XLPE (Aluminium) if back up fuse is provided.

5. Fire separation walls shall be provided in between oil filled transformers. Thickness of the wall shall be minimum 30 cm (Brick) or 20 cm (RCC)

6. Oil filled transformers shall be segregated from HT and MV switchgears using fire separation wall

7. Oil drainage facility/soak pits shall be insisted for oil filled transformers if quantity of oil is more than 2000 litres.

8. All-round clearance shall be provided for indoor transformers. It shall be minimum 1.25m if walls are provided at 4 sides.

9. Transformers shall be installed at the periphery of the building for getting easy access and adequate ventilation.

10. Doors and windows of transformer room shall be of non-inflammable materials.

11. Minimum 50 cm headroom clearance shall be provided for the transformer.

a). If dry type transformers are installed above ground level, emergency switching off facility shall be provided at ground floor.

b). Structural fitness certificate from a competent structural engineer shall also be furnished.

13. Minimum phase to phase and phase to earth clearance of bus bars in 11 kV panel shall be 130 mm and 80 mm respectively.

14. Minimum 1.0 metre clear space shall be available in front of HT panel in breaker drawn out position.


  1. what is the fullform of ABSF?

  2. ABSF means Air Break Switch Fuse unit, the type you usually see on the primary side of distribution transformers.

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  5. the clearance mentioned here for 1.25m where do i find this rule in the electriclity act or rules
    or any other please do mention the section or clause which states it

  6. A Oil filled transformers is used to deliver electrical energy from a primary source or distribution circuit to a secondary source. The size of the transformer depends on the desired capacity.

  7. Hi, what a great web blog. I usually spend hours on the net reading blogs on various subjects. And, I really would like to praise you for writing such a fabulous article Cast resin transformer

  8. Thanks otd strans, your comments were very motivating. However, I must confess that most of the articles published were collected from various sources and I cannot claim credit for them!

  9. Pls any one can tell me, whats should be the clearance between power transfromer(outdoor) and firewall.

  10. Transformer manufacturing companies tend to be always wanting to get the business enterprise from the power, commercial along with industrial sector. Many companies producing Power transformers in India. Power transformers that will establish the service dependably with the web page, Cost-efficient along with secure through the entire ages.

  11. Sushil Sahu, you may refer to the new article I posted today, Spatial Clearances for Transformer Installation ( I have included some info I could obtain from various standards and regulations.

  12. Does that mean that Transformer firewall is not required for trafos below 2000 ltr capacity.
    Please tell me when firewall is required between two trafos and the indian standard code

  13. Thanks for sharing this article. nice post. We also manufacturers of Control TransformersControl Transformers Manufacturers

  14. I read your Dry Type Transformer blog it was so nice and thanks for blogging. keep Blogging. We are also Manufacturers and Supplier of Dry Type Transformer in Tamil Nadu, India.

  15. Very impressive article. I got many information from your unique content. This would have helped many like me in finding the best On line ups Dealers in Chennai

  16. what level of clearance required for 2 no of 200 kva transformer lying parallel to each other . on standerd structure .in mid of market

  17. Is this great post, I really like your every posts can you sir post about High Tension Transformers , I just buy this last month.

  18. Whether soak pit required for outdoor transformer? If yes what is the minimum oil quantity?

  19. Transformers are basically the equipment used to transfer electrical energy from power plants to homes and industries. This power has to travel long distances before reaching its destination, which is why it gets altered. It is of very high voltage when it begins from its source but, it gets lowered when it reaches its sub-station, and steps down even more when it reaches the transformer.
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  20. These technical details had been of great help. Thanks for sharing!!Keep updating new posts on your blog!!
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  21. Could you please let me know what is the safe distance to be maintained from adjacent buildings for a 11000 KV dry transformer installation, Could you please quote the section/clause of the Indian Electricity Act