An oil-immersed and dry-type transformer manufacturer China that builds both families keeps one loss table, one drawing datum and one test list. XIAOPAI works that way from a single plant in Zhejiang, and ships both families to projects in South America and Africa.
That arrangement follows the projects rather than the catalogue. A project in either market usually needs both structures before it needs either one alone, and the reason is visible on the single line diagram rather than in a preference for one technology.
WHAT ONE PROJECT ACTUALLY NEEDS
Take the single line diagram of a rural or peri-urban project in either market. The feeder that leaves town runs single-phase pole-mounted units of 5 to 100 kVA, at 11, 10.5, 10 or 6.3 kV with a 0.22 or 0.24 kV secondary. Those poles carry oil-immersed units, and the catalogue builds them as a separate single-phase range with its own loss table.
Where the same feeder reaches the town, the load steps up to a 35 kV oil-immersed unit at the substation. That unit is sized against the feeder current and against the factory transformer behind it, and it sits outdoors in a compound with a bund, which is where an oil-filled unit belongs.
The factory room is where the second structure enters the drawing. A dry-type unit needs no oil pit, no bund and no oil sampling, and it puts the fire load inside a room that already has ventilation and a boundary sound limit. In a plant that has to insure the building, that difference is worth more than a few hundred watts.
Three duties, two structures, one specification. What each structure has to be is the next question, and it is answered by the ranges rather than by the sales sheet.
WHAT THE TWO FAMILIES COVER
The oil range runs from S9 to S22, built from 30 to 2,500 kVA at 10 kV, with the single-phase pole-mounted range from 5 to 100 kVA alongside it. At 35 kV the same family runs from 50 to 5,000 kVA, which covers a town substation and the step-down behind it.
The dry range is SC(B)9 to 13, epoxy cast, also built from 30 to 2,500 kVA at 10 kV and available at 35 kV in the same ratings. Both families use Yyn0 or Dyn11 vector groups, 4 % or 4.5 % impedance and a tap range of ±5 % in ±2 × 2.5 % steps. A specification written for one can be read against the other without translation.
Both are built and tested to GB 1094.1 through 1094.5, GB/T 6451, GB/T 1094.10, JB/T 10088, IEC 60076, ANSI/IEEE C57.12.00 and C57.12.10, and SANS 780. Both are rated for altitude below 1,000 m, +40 °C maximum air, +30 °C daily mean, +20 °C annual mean and a lowest outdoor temperature of −25 °C. A site outside that envelope is declared at the enquiry, because the loss values move with it.
Same specification, same test list, different behaviour once the unit is energised. That difference is where the buyer's decision actually sits, and it can be read from one table.
HOW THE TWO FAMILIES DIFFER IN SERVICE
| Rating | Oil S13-M no-load | Oil S13-M load | Dry SC(B)10 no-load | Dry SC(B)10 load | Dry sound |
|---|---|---|---|---|---|
| 100 kVA | 150 W | 1,500 W | 400 W | 1,570 W | 48 dB |
| 630 kVA | 570 W | 6,200 W | 1,300 W | 5,960 W | 51 dB |
| 1,250 kVA | 970 W | 12,000 W | 2,090 W | 9,690 W | 52 dB |
| 2,500 kVA | 2,040 W | 21,200 W | 4,000 W | 17,170 W | 53 dB |
The table compares two 10 kV series at four ratings. Reading the no-load columns first, the dry unit draws 2.67 times the oil figure at 100 kVA, 2.28 times at 630 kVA, 2.16 times at 1,250 kVA and 1.96 times at 2,500 kVA. Staying energised is the expensive half of a dry-type unit, and the premium thins out as the unit grows.
The load columns run the other way. The dry unit is 4.7 % higher at 100 kVA, 3.9 % lower at 630 kVA and 19 % lower at 1,250 and 2,500 kVA. The two columns swap places somewhere between 630 and 1,250 kVA. One caveat belongs here. The oil figures are quoted at 75 °C and the dry figures at 120 °C. Bringing both to 75 °C lowers the dry load loss by about 12 %, which widens its advantage at 630 kVA from 3.9 % to 16 %.
Put the two halves together and the decision turns on the load factor. At 1,250 and 2,500 kVA the dry unit uses less energy once the plant runs above roughly 70 % of rating. At 630 kVA and below no load factor closes the gap, so the oil unit wins on energy at every load. At 2,500 kVA, half load leaves the dry unit 8,344 kWh behind over a year, while 80 % load puts it 5,424 kWh ahead.
Weight is the argument buyers expect, and in these two series it does not carry. At 1,250 kVA the dry unit is 3,450 kg against 3,370 kg, a difference of 80 kg. What does carry is the room. The dry unit needs ventilation and a boundary sound limit of 46 to 53 dB, and it removes the oil pit, the bund and the dissolved gas routine that catches fault gases in oil. An oil unit keeps all of that and repays it with the lower no-load loss, which is why the fire load usually settles a room before the loss table is opened.
Fluid choice inside the oil family is a separate question with its own trade-offs, as the retreat from silicone fluids shows, but it does not change the arithmetic on this page. What changes it is the load factor, and the load factor belongs to the buyer.
WHAT THE ENQUIRY HAS TO CARRY
Because the answer moves with the load factor, the enquiry has to carry it. Six items do that. The load profile comes first, hourly if possible and day against night at minimum, because peak kVA on its own cannot produce a load factor. Then the site ambient, the altitude, indoor or outdoor, whether oil is permitted on site, and the sound limit at the boundary.
The rest is specification, and both families use the same fields: rating in kVA, voltage class, tap range, vector group, impedance and cable box entry. Altitude above 1,000 m is declared separately, because it changes the design rather than the model number. A dry-type order adds the enclosure and the sound limit; an oil order adds the conservator or sealed-tank choice and the oil containment arrangement.
With those in hand one enquiry covers both families, and the two quotations come back on the same basis rather than on two sets of assumptions. That is the practical difference between buying from an oil-immersed and dry-type transformer manufacturer China and buying the two structures from two suppliers who never compare notes.
WHY ONE SOURCE FOR BOTH
The comparison above rests on values from a single catalogue, and that is the point of buying both families from one plant. One loss table, one drawing datum, one routine test list and one technical contact carry across the whole order, so a change to the room does not reopen the transformer discussion from the beginning.
Both families run to 35 kV as well, in the S9 to S22 oil range and the SC(B)9 to 13 dry range. The incoming breaker is set against the transformer's rated current rather than its capacity, which is another decision that gets simpler when one party holds both files.
The last reason is regulatory rather than technical. Efficiency rules in export markets keep moving, and regulators now read the loss column as closely as buyers do, which is the argument behind the debate over distribution transformer efficiency standards. A unit chosen on one number tends to be re-read on the other a few years later, and operation and maintenance keeps returning to the same two figures.
Both structures leave the same plant, on the same drawings and the same test bench, and the choice between them is settled with two figures from one table.
XIAOPAI manufactures oil-immersed and dry-type transformers and supplies both families to projects in South America and Africa. Loss values in this article are catalogue figures for the S13-M oil-immersed series and the SC(B)10 dry-type series at 10 kV. Configuration lists, delivery schedules and commercial terms are issued separately for each project.
