Indian Compliance
BIS Certification for Distribution Transformers (IS 1180): Process, Testing & Cost
Distribution transformers are one of the products where the ISI mark matters most commercially. Electricity distribution companies, EPC contractors and private buyers will not accept a transformer without it, and without it the transformer cannot legally be sold.
In short: outdoor oil-immersed distribution transformers covered by IS 1180 (Part 1):2014 need a BIS licence and the ISI mark under the Electrical Transformers (Quality Control) Order. They also need a BEE star label. The licence process involves an in-house test lab, a BIS factory inspection and independent testing.
What IS 1180 Covers
IS 1180 (Part 1) applies to:
- Outdoor type, oil-immersed distribution transformers
- Three-phase and single-phase units
- Ratings up to 2,500 kVA and voltage up to 33 kV
- Natural air and oil cooling (ONAN)
The standard sets ratings, losses, temperature rise, impedance, fittings and tests. It works with the IS 2026 series, which covers general power transformer requirements and test methods. Read the requirements in our electrical transformers standard page.
Energy Efficiency Levels
IS 1180 defines three energy efficiency levels. Each sets maximum total losses at 50% and 100% load for every standard rating:
- Level 1: the base level
- Level 2: lower losses
- Level 3: the lowest losses, usually needing better core steel such as CRGO or amorphous metal
The level you design to affects material cost, and it links to the BEE star rating. Many utility tenders specify the minimum level or star rating they accept.
Tests for Distribution Transformers
| Type | Tests |
|---|---|
| Routine tests (every unit) | Winding resistance, voltage ratio and polarity or vector group, no-load loss and current, load loss and impedance voltage, insulation resistance, separate-source voltage withstand, induced over-voltage withstand, oil leakage |
| Type tests (per design) | Temperature rise, lightning impulse, pressure and vacuum tests on the tank |
| Special tests | Short-circuit withstand (dynamic), and others agreed with the buyer |
The factory must be able to do the routine tests in-house. Type and special tests are usually done in an accredited high-power or high-voltage lab. Short-circuit testing needs a specialised lab and adds cost and waiting time, so book it early.
BIS Licence Process for IS 1180
- Check scope and ratings. List the kVA ratings, voltage classes and efficiency levels you want covered.
- Set up the test bay. The in-house lab must match the BIS product manual: loss measurement, ratio, resistance, high-voltage tests and calibrated instruments.
- Prepare quality records. Incoming checks for core steel, copper or aluminium, oil and bushings, process records and test records.
- Apply on Manak Online with documents and fees.
- Factory inspection. BIS officers see tests performed and draw samples.
- Independent testing of samples in a BIS or BIS-recognised lab.
- Grant of licence with a CM/L number, after which each transformer carries the ISI mark on its rating plate.
Foreign transformer makers apply under FMCS.
BEE Star Labelling
Distribution transformers are under BEE's mandatory star labelling programme. The star rating depends on total losses at 50% and 100% load. BEE has notified a revised loss table from 1 January 2027, so ratings designed to the old table may lose stars. Plan redesigns and retests before that date. See our BEE certification services.
Cost and Timeline
The cost has four parts: BIS fees (application, annual licence and marking fees), in-house lab set-up, independent testing of samples and, where needed, type and short-circuit tests in a high-power lab. Short-circuit tests are the most expensive single item and depend on the rating.
For time, a well-prepared factory with a ready lab can expect the BIS licence in a few months. Delays usually come from incomplete in-house testing, waiting for lab slots or test failures on losses.
Common Mistakes
- Losses too close to the limit. Variation between units can push some over the maximum. Design with a margin.
- Uncalibrated loss measurement. BIS checks calibration of power analysers, CTs and PTs.
- Ignoring the 2027 BEE table. A rating that passes today may need a redesign.
- Wrong rating plate. The plate must show the ISI mark, licence number, IS number, efficiency level and other details required by the standard.
How Instacertify Helps
We review your designs against IS 1180, audit the test bay, prepare documents, coordinate type tests and support the BIS inspection and BEE registration. Start with our ISI mark service for Indian manufacturers.
Frequently asked questions
Is BIS certification mandatory for distribution transformers?
Yes. Outdoor oil-immersed distribution transformers covered by IS 1180 (Part 1) must carry the ISI mark under the Electrical Transformers (Quality Control) Order. Making, selling or importing them without a BIS licence is not allowed.
Which transformers does IS 1180 Part 1 cover?
Outdoor type, oil-immersed, three-phase and single-phase distribution transformers up to 2,500 kVA and 33 kV, with natural cooling.
What are energy efficiency levels in IS 1180?
IS 1180 sets three energy efficiency levels, Level 1, 2 and 3, each with maximum total losses at 50% and 100% load. Level 3 is the most efficient.
Do distribution transformers also need a BEE star label?
Yes. BEE star labelling is mandatory for distribution transformers in its scope. BEE has notified a revised loss table that applies from 1 January 2027, so check the current schedule when designing new ratings.
Is the short-circuit test required for the BIS licence?
The short-circuit withstand test is a special test under IS 1180 and is usually done on a representative rating at a high-power lab. BIS and buyers decide when it is required, so confirm with the product manual and the tender.
Can one BIS licence cover several kVA ratings?
Yes. A licence can cover a range of ratings and voltage classes, provided the factory can test them and the samples tested represent the range as per the BIS guidelines.
