16 kVA – 1000 kVA
Distribution Transformers
Oil-immersed, ester-filled and dry type distribution transformers from 16 kVA to 1000 kVA (1 MVA) in the 11 kV and 33 kV classes, with CRGO or amorphous cores — built to IS 1180 and IS 2026, to any energy-efficiency level, and to your vector group and impedance rather than only ours.
Finished distribution transformers in the dispatch yard
Overview
Sustained distribution-class output across the rating range.
The full IS 1180 distribution ladder, single and three phase.
Built to whichever IS 1180 efficiency level your tender specifies.
Any rating in the distribution class.
Distribution transformers are the highest-volume line on the campus — around 900 jobs a month across the full IS 1180 rating ladder, from 16 kVA agricultural units to 1000 kVA industrial supply.
Standard build is Dyn11, ONAN, 11/0.433 kV or 33/0.433 kV, with off-circuit tapping. But almost nothing here is fixed: vector group, impedance, tapping range, winding material, fittings and efficiency level are all specified by the purchaser, and we build to that schedule rather than asking you to accept ours.
Technical data
Specification.
Built to the purchaser's schedule. Fields marked On enquiry are issued against a specific enquiry. Delivery as per the client's requirement, confirmed with the quotation. Open the rows below for construction details, reference tables and fittings.
General
| Parameter | Specification |
|---|---|
| Rated capacity | 16 kVA to 1000 kVA (1 MVA) |
| Phases | Three-phase and single-phase |
| Type | Oil-immersed, outdoor — sealed corrugated-tank or conservator type; dry type (AN) for indoor duty |
| Voltage class | 11 kV, 22 kV and 33 kV systems |
| Standard voltage ratios | 11 / 0.433 kV · 22 / 0.433 kV · 33 / 0.433 kV · 11 / 0.25 kV single-phase |
| Frequency | 50 Hz standard; 60 Hz for export |
| Cooling | ONAN; ONAF on larger ratings; KNAN with natural ester fluid; AN for dry type |
| Mounting | Pole, plinth or platform — pole mounting up to 500 kVA by agreement |
| Duty | Continuous, outdoor |
| Applicable standards | IS 1180 (Part 1), IS 2026 (Parts 1–5), IEC 60076 for export |
Electrical
| Parameter | Specification |
|---|---|
| Vector group | Dyn11 standard; Dyn1, Dyn5, YNyn0, Yzn11 and others to order |
| Impedance | Per IS 1180 — 4.50% up to 630 kVA, 5.00% above 630 kVA to 1000 kVA (±10%) |
| Tapping | Off-circuit tap changer, +5% to −10% in 2.5% steps (7 positions); ranges to order |
| Energy efficiency | IS 1180 Level 1 to Level 5 — specify the level required |
| No-load current | ≤ 3% of full-load current up to 200 kVA; ≤ 2% above 200 kVA |
| Insulation level (BIL) | 75 kVp at 11 kV; 125 kVp at 22 kV; 170 kVp at 33 kV |
| Temperature rise | 45 K winding by resistance, 40 K top oil, over 50 °C ambient |
| Insulation class | Class A |
| Guaranteed losses | As per technical specification — no-load and load losses guaranteed per rating against the purchaser's schedule |
Construction and further particularsMaterials, tank, paint and mechanical details
Construction
| Parameter | Specification |
|---|---|
| Core | CRGO silicon steel lamination to IS 3024, step-lap mitred, or amorphous metal core for the lowest no-load loss |
| Windings | Copper or aluminium — specify; layer or helical construction by rating |
| Insulating fluid | Mineral transformer oil to IS 335:2018, or natural ester (K-class) fluid to IEC 62770; none in dry type units |
| Tank | Fabricated plain or corrugated; corrugation minimum 1.0 mm per IS 1180 |
| Surface preparation | Shot blasted to Sa 2½ (ISO 8501-1) |
| Painting | Interior hot-oil-resistant ≥ 35 µm; exterior powder or epoxy-PU, shade 631 per IS 5 |
| Mounting channels | Minimum 75 × 40 mm up to 200 kVA |
| Pressure test | 100 kPa plain tanks; 15 kPa corrugated tanks per Amendment 4 |
Reference data — what the standards requireTables from the Indian Standard, for checking any quotation against it
Standard ratings and impedance
| Nominal system voltage | Standard ratings (kVA) |
|---|---|
| Up to and including 11 kV | 6.3*, 10, 16, 20*, 25, 40*, 63, 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000 |
| Above 11 kV up to 22 kV | 63, 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000 |
| Above 22 kV up to 33 kV | 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000 |
* Non-preferred rating. Amendment 4 (2021) extends the small-rating list to all voltage classes.
| Rating band | Percentage impedance |
|---|---|
| 16 – 630 kVA, three-phase | 4.50% |
| 800, 1000 kVA, three-phase | 5.00% |
| 5 kVA, single-phase | 2.50% |
| 10 – 100 kVA, single-phase | 4.00% |
Tolerance ±10% per IS 2026. Most DISCOM specifications write this as “±10%, no negative tolerance”.
Energy efficiency levels
IS 1180 does not cap no-load and load loss separately. It caps total loss at 50% and at 100% load, and lets the designer trade one against the other. Amendment 4 of March 2021 deleted the loosest level and added two tighter ones, so there are now five levels — a great deal of material still in circulation quotes the old three-level numbering, under which today's Level 1 was called Level 2.
| kVA | %Z | Level 1 50% / 100% | Level 2 50% / 100% | Level 3 50% / 100% | Level 4 50% / 100% | Level 5 50% / 100% |
|---|---|---|---|---|---|---|
| 16 | 4.5 | 135 / 440 | 120 / 400 | 108 / 364 | 97 / 331 | 87 / 301 |
| 25 | 4.5 | 190 / 635 | 175 / 595 | 158 / 541 | 142 / 493 | 128 / 448 |
| 63 | 4.5 | 340 / 1140 | 300 / 1050 | 270 / 956 | 243 / 870 | 219 / 791 |
| 100 | 4.5 | 475 / 1650 | 435 / 1500 | 392 / 1365 | 352 / 1242 | 317 / 1130 |
| 160 | 4.5 | 670 / 1950 | 570 / 1700 | 513 / 1547 | 462 / 1408 | 416 / 1281 |
| 200 | 4.5 | 780 / 2300 | 670 / 2100 | 603 / 1911 | 543 / 1739 | 488 / 1582 |
Watts. Both caps must be met: total loss at 50% load and at 100% load. The 50% figure is usually the binding one, and it is what drives low no-load-loss design.
| kVA | %Z | Level 1 50% / 100% | Level 2 50% / 100% | Level 3 50% / 100% | Level 4 50% / 100% | Level 5 50% / 100% |
|---|---|---|---|---|---|---|
| 250 | 4.50 | 980 / 2930 | 920 / 2700 | 864 / 2488 | 811 / 2293 | 761 / 2113 |
| 315 | 4.50 | 1025 / 3100 | 955 / 2750 | 890 / 2440 | 829 / 2164 | 772 / 1920 |
| 400 | 4.50 | 1225 / 3450 | 1150 / 3330 | 1080 / 3214 | 1013 / 3102 | 951 / 2994 |
| 500 | 4.50 | 1510 / 4300 | 1430 / 4100 | 1354 / 3909 | 1282 / 3727 | 1215 / 3554 |
| 630 | 4.50 | 1860 / 5300 | 1745 / 4850 | 1637 / 4438 | 1536 / 4061 | 1441 / 3717 |
| 800 | 5.00 | 2287 / 6403 | 2147 / 5838 | 2015 / 5323 | 1892 / 4853 | 1776 / 4425 |
| 1000 | 5.00 | 2790 / 7700 | 2620 / 7000 | 2460 / 6364 | 2310 / 5785 | 2170 / 5259 |
Above 11 kV up to 22 kV, permitted losses are 5% higher; above 22 kV up to 33 kV, 7.5% higher. IS 1180 allows no positive tolerance on maximum total losses.
Insulation, temperature rise and tapping
| Nominal system voltage | Impulse withstand (kVp) | Power-frequency withstand (kV rms) |
|---|---|---|
| 3.3 kV | 40 | — |
| 6.6 kV | 60 | — |
| 11 kV | 75 | 28 |
| 22 kV | 125 | 50 |
| 33 kV | 170 | 70 |
| Class | Winding rise (by resistance) | Top-oil rise (by thermometer) | Ambient basis |
|---|---|---|---|
| Three-phase up to 200 kVA (IS 1180) | 40 K | 35 K | 50 °C |
| Three-phase above 200 up to 2500 kVA (IS 1180) | 45 K | 40 K | 50 °C |
| Single-phase up to 25 kVA (IS 1180) | 40 K | 35 K | 50 °C |
| IEC 60076-2 baseline | 65 K (average) | 60 K | 40 °C |
Indian limits are materially stricter than the IEC baseline. Export buyers reading IEC numbers will not otherwise realise this.
| Class | Tap positions | Range |
|---|---|---|
| Three-phase up to 200 kVA | 4 | +2.5% to −5% of HV in 2.5% steps |
| Three-phase above 200 up to 2500 kVA | 7 | +5% to −10% of HV in 2.5% steps |
| Power transformer, off-circuit (utility practice) | 7 | +5% to −10% in 2.5% steps |
| Power transformer, on-load (utility practice) | 17 | +5% to −15% in 1.25% steps |
Standard and optional fittingsWhat is supplied as standard, and what is available to order
Standard Fittings
Supplied as standard
- Two earthing terminals with earthing symbol
- Rating plate and terminal marking plate
- Oil level gauge marked minimum / 30 °C / maximum
- Air release device and silica-gel dehydrating breather
- Drain-cum-sampling valve — three-phase above 500 kVA
- Thermometer pocket with cap
- Lifting lugs for the complete unit and for the core-and-winding assembly
- Pressure relief device — all sealed types, and above 200 kVA
- Filter valve on the upper side above 200 kVA
- HV neutral grounding strip and arcing horns on the HT side
- Buchholz relay above 1000 kVA
Optional Fittings
Available to order
- Enhanced dehydrating breather on ratings up to 200 kVA
- Lightning arrestors and bird guards
- Bimetallic terminal connectors to IS 5561
- Oil and winding temperature indicators above 200 kVA
- Magnetic oil level gauge and jacking pads above 1600 kVA
- Buchholz relay as an option above 200 kVA
- Non-return valve and protection relay on sealed units
- Anti-theft fasteners and locking caps on valves
- Unidirectional rollers above 200 kVA
- LV cable box with MCCB or distribution board
- Conservator with drain plug
Compliance
Standards & testing.
Routine tests are performed on every unit before dispatch. Type tests are certified from CPRI, ERDA or NABL-accredited laboratories on request.
| Standard | Scope |
|---|---|
| IS 1180 (Part 1):2014 | Outdoor oil-immersed distribution transformers up to 2500 kVA, 33 kV — including the energy-efficiency levels |
| IS 2026 (Parts 1–5) | Power transformers — general, temperature rise, insulation levels, terminal markings, short-circuit withstand |
| IEC 60076 series | International power transformer standard — the export equivalent |
| IS 3024 | Cold-rolled grain-oriented (CRGO) electrical steel sheet and strip |
| IS 335:2018 | Insulating mineral oil for transformers and switchgear |
| IS 3639:1966 | Fittings and accessories for power transformers |
| IS 2099 / IS 7421 | HV and LV porcelain bushings |
| IS 3637 | Gas-and-oil-operated (Buchholz) relays |
| IS 5:2007 | Colours for ready-mixed paints — shade 631 for distribution, 632 Admiral Grey for power |
| IS 6600:1978 | Guide for loading of oil-immersed transformers |
Routine and type testsPerformed on every unit, and available on request
Routine tests
Performed on every unit
- Winding resistance at each tap — IS 2026 (Part 1) cl. 16.2
- Voltage ratio, polarity, phase sequence and vector group — cl. 16.3
- Short-circuit impedance and load loss at 50% and 100% — cl. 16.4
- No-load loss and no-load current at 90%, 100% and 112.5% voltage — cl. 16.5
- Insulation resistance — cl. 16.6
- Separate-source voltage withstand — IS 2026 (Part 3) cl. 10
- Induced overvoltage withstand — IS 2026 (Part 3) cl. 11
- Pressure test — IS 1180 (Part 1) cl. 21.5.1.2
- Oil leakage test — IS 1180 (Part 1) cl. 21.5.1.3
- Oil breakdown voltage and moisture content — IS 335:2018
Type & special tests
Available on request
- Lightning impulse test — IS 2026 (Part 3) cl. 12
- Temperature-rise test — IS 2026 (Part 2) cl. 4
- Short-circuit withstand — IS 2026 (Part 5)
- Sound level determination — IS 2026 (Part 10)
- Paint adhesion, cross-hatch — ASTM D3359
- Magnetic balance test, HV and LV — CBIP Publication 317
- IP55 verification of cable box — IS/IEC 60529
Purchaser and third-party pre-dispatch inspection is accommodated on request, including for export consignments. Type-test certificates are issued from CPRI, ERDA or NABL-accredited laboratories — copies available on request.
Inside the works
Where the tank is made.
Tank fabrication, radiator assembly and paint are all our own operations — not bought-in sub-assemblies finished under our name.
Walk the whole works
Applications
Where it goes to work.
Distribution networks
Rural and urban feeders under national electrification and distribution strengthening programmes.
Agricultural feeders
Pump-set and tube-well supply, including separated agricultural feeder schemes.
Industrial supply
Plant, warehousing and industrial estate supply at the higher end of the rating range.
Developments
Township, institutional and commercial complex distribution.
Questions
Frequently asked.
What is the smallest and largest distribution transformer you manufacture?
Which vector group do you supply?
Can you meet a specific IS 1180 energy efficiency level?
Do you supply copper or aluminium windings?
Often supplied together
Send us your transformer schedule.
Share the ratings, voltage class, vector group, impedance, loss level and quantity required, and we will return a quotation with a firm delivery programme.