Transformer for a Factory: kVA, Type, Losses and Cost Drivers

The cost of a factory transformer is set by its kVA rating, voltage class, type (oil-filled or dry), core and winding material, loss level, protection fitted, and the substation works around it. Size the kVA from coincident demand: planning kVA equals present plus future coincident kW, divided by power factor and the loading you are willing to plan to. We quote no price here; use the drivers below to compare bids.

How do you size the kVA?

Start from demand, not from the sum of nameplates. Take the coincident kW that actually runs together at peak, from a metered maximum demand or a load schedule with diversity applied. Add the coincident demand you expect to add over the planning period. Divide by the power factor the transformer will see and by the share of its rating you are prepared to load it to. The result, in kVA, is the planning rating, and you choose the smallest standard rating at or above it. Our transformer sizing calculator does exactly this arithmetic with your own ratings list.

An illustration with made-up round numbers: present coincident demand 600 kW, future 200 kW, power factor 0.95, planned loading 80%. That is 800 kW divided by 0.76, or about 1,053 kVA, so the next preferred rating up is 1,250 kVA. The 80% is a planning choice, not a rule, and a small change in power factor or loading moves the answer, which is why the calculator shows the sensitivity. Harmonics from drives, ambient temperature, fault level, impedance and standby philosophy are engineering checks beyond this arithmetic. Our note on transformer undersizing as a growth bottleneck explains why the rating is the hardest ceiling in a factory's electrical system to raise later.

Oil-filled or dry type?

The CEA safety regulations of 2023 decide part of this. Regulation 46 says oil-filled transformers installed indoors in buildings other than residential or commercial must be on the ground floor or no lower than the first basement, and that only dry-type transformers are used inside residential and commercial buildings. For a substation or switching station with more than 2,000 litres of oil in an apparatus, it asks for fire barrier walls where the adjacent building wall is not rated for four hours, an oil soak pit, and no storage of spare oil nearby; above 9,000 litres in one tank it asks for draining arrangements and fire precautions. It also bars a substation with more than 2,000 litres of oil in a basement where proper draining cannot be provided. For a standalone factory transformer yard, oil-filled units are usually the economical choice; indoors, near stores or in a basement, dry type may be forced by the regulation or by the fire scheme. Our fire-fighting systems team can say which the fire authority will accept.

Which standard and which tests?

IS 1180 (Part 1):2014 covers three-phase distribution transformers up to and including 2,500 kVA, for nominal system voltages up to 33 kV, and the BIS product manual shows the core can be CRGO or amorphous and the winding copper or aluminium, with energy efficiency levels declared. The routine tests listed there include winding resistance, voltage ratio and phase displacement, short-circuit impedance and load loss at 50% and 100% load, no-load loss and current, insulation resistance, induced and separate-source voltage withstand, and pressure and oil-leakage tests. Type tests include a lightning impulse test and a temperature-rise test. Ask the bidder for the BIS licence number and the test certificates of the exact rating, and write witnessed routine tests into the purchase order if the load justifies it. Regulation 48 of the CEA regulations also asks for site tests on apparatus above 650 V before commissioning.

What drives the cost?

How do losses affect the bid comparison?

A transformer is energised all day, every day. The no-load (core) loss runs continuously whatever the factory is doing, while the load loss rises with the square of the load current. A cheaper unit with higher losses can therefore cost more over its life than a dearer low-loss unit, particularly in a factory with a steady load. Compare bids on three lines: purchase price, guaranteed no-load loss and guaranteed load loss at your expected loading. Convert the guaranteed losses to annual energy at your own tariff and add that to the price, or ask the supplier to show the comparison. We do not publish a loss-capitalisation rate because it depends on your tariff and horizon.

How does the rating affect approvals?

The rating decides who approves the drawings. Karnataka's March 2025 delegation of powers, for example, assigns consumer HT transformer installations to different officers by capacity: up to 200 kVA, above 200 to 500, above 500 to 2,000, above 2,000 to 5,000 and above 5,000 kVA. Other states use other bands, but the principle is the same: crossing a threshold changes the office, the checklist and the time. Our guide to CEIG approval for factories covers the file, and the CEIG readiness calculator checks your documents.

How Secured Engineers helps

We size transformers and design the substation in-house, with the single-line diagram, protection schedule and CEIG drawings prepared together, and Fire NOC, CEIG and DISCOM filings handled in-house. MEPF and solar can be delivered under one contract, which matters when the same transformer will also take a solar plant's export. We work from our Noida (Delhi NCR) and Ludhiana offices across 535+ projects in 18+ states, with 89.77% repeat clients. See also our guide to transformer headroom for solar.

To have a budget or a bid reviewed line by line, see our transformer and DG set service, message us on WhatsApp, call +91 70099 85817, or send the bid with a free proposal request.