If you are evaluating distribution transformer bids and one supplier offers “IS 1180 Level 2” while another offers “Level 1”, you may not be comparing what you think you are comparing. There is a reasonable chance both are describing the same losses.
What the levels actually cap
The first thing to understand is that IS 1180 does not mandate separate no-load and load loss figures. It caps total losses — no-load plus load — at two operating points, and lets the designer trade one component against the other so long as both caps are met:
- Total loss at 50% load: no-load loss + 0.25 × load loss
- Total loss at 100% load: no-load loss + load loss
That 50% figure is usually the binding constraint, and it is what pushes designers towards low no-load loss — better CRGO grades, and in some cases amorphous cores. A design that comfortably meets the 100% cap can still fail the 50% one.
The renumbering
IS 1180 (Part 1):2014 originally defined three levels. Amendment No. 4, issued in March 2021, deleted the loosest level, renumbered what remained, and added two new tighter levels. There are now five.
The effect is easiest to see on a single rating. Under the pre-2021 tables a 315 kVA unit at Level 1 was capped at 1100 W and 3275 W; at Level 2, 1025 W and 3100 W; at Level 3, 955 W and 2750 W. Under Amendment 4, the same rating reads:
| kVA | %Z | Level 1 50% / 100% | Level 2 50% / 100% | Level 3 50% / 100% | Level 4 50% / 100% | Level 5 50% / 100% |
|---|---|---|---|---|---|---|
| 315 | 4.50 | 1025 / 3100 | 955 / 2750 | 890 / 2440 | 829 / 2164 | 772 / 1920 |
Read that against the old numbering and the point is obvious: today's Level 1 is the old Level 2, and today's Level 2 is the old Level 3. Anyone quoting pre-2021 level numbers is overstating their compliance by one full step — usually without realising it, because the marketing copy was written in 2018 and never revisited.
What to do about it in a tender
Three practical steps.
Ask for the watts, not the level. A level number is an abbreviation. The maximum total loss at 50% and at 100% load, in watts, for the specific rating, is the actual requirement. Put those two numbers in the schedule and the ambiguity disappears.
State the amendment. Write “IS 1180 (Part 1):2014 as amended to Amendment No. 4:2021” in the specification. It takes eight words and removes the entire problem.
Check the tolerance clause. IS 2026 and IEC 60076-1 allow +15% on each individual loss component and +10% on the total. IS 1180 and effectively every DISCOM specification override this: no positive tolerance is permitted on maximum total losses. Loss penalties in Indian tenders currently run in the region of ₹250 per watt on distribution transformers. On a 315 kVA unit, being 100 W over is not a rounding error.
Higher voltage classes
The published tables are for the 11 kV class. Above 11 kV up to 22 kV, permitted losses are 5% higher for three-phase units; above 22 kV up to 33 kV, 7.5% higher. For single-phase units the uplifts are 7.5% and 10% respectively. A 33 kV class transformer quoted against the 11 kV table is being held to a stricter figure than the standard requires — which is a mistake in the buyer's favour, but a mistake nonetheless.
The short version
Specify the level, the amendment and the watts. Ask every bidder to state guaranteed no-load and load loss separately against the cap. And if a quotation cites a level without a year or an amendment number, ask which edition they mean before you compare it with anything.
