Transformer Academy
A practical starting point for new XinHuan staff, EPC buyers, distributors, and procurement teams: what transformers do, how to read the main ratings, when to choose oil or dry-type, and what to send in an RFQ.
Guided Path
A transformer changes AC voltage from one level to another. It can step voltage up for transmission or step voltage down for factories, buildings, mining sites, substations, and distribution networks. It does not change AC into DC, and it does not change 50 Hz into 60 Hz.
These are the first ratings a buyer should understand. kV describes voltage level. kVA or MVA describes transformer capacity. Hz and phase must match the grid or site power system.
Voltage level
Example: 11kV/0.4kV. The transformer connects one voltage class to another.
Apparent power
Capacity rating. 1000 kVA = 1 MVA. Use load data before choosing a size.
Frequency
Usually 50 Hz or 60 Hz. The transformer must match the project grid.
1-phase / 3-phase
Most utility, EPC, and industrial transformers are three-phase.
Need a first sizing estimate? Use the transformer kVA calculator.
Oil-immersed transformers use insulating oil as both insulation and cooling medium. Dry-type transformers use air and solid insulation, often with cast resin coils, and are common indoors where oil containment or fire-risk rules matter.
For a full buyer comparison, read oil-immersed vs dry-type transformer selection, or browse oil-immersed transformers and dry-type transformers.
Usually lower voltage and smaller capacity, often 11kV or 33kV down to 400V/415V for factories, buildings, and local grids.
Used at higher voltage and larger MVA ratings in substations, generation, transmission, and heavy industrial systems.
Many Africa, Middle East, and IEC-grid projects use 11kV and 33kV distribution levels at 50 Hz. Latin America and some other markets often require 60 Hz and ANSI/IEEE style voltage classes such as 13.8kV or 34.5kV.
Cooling code tells you how heat leaves the transformer. ONAN uses natural oil circulation and natural air. ONAF adds fans to move more air across radiators. Dry-type units commonly use AN or AF.
Deep dive: ONAN vs ONAF transformer cooling.
Transformer losses have two main parts. No-load loss happens whenever the transformer is energized. Load loss rises roughly with the square of the load. This is why a cheaper unit can become more expensive over years of operation.
Compare options with the transformer loss calculator.
Routine tests are factory tests that verify the transformer before shipment: winding resistance, voltage ratio, vector group, impedance, load loss, no-load loss, insulation resistance, applied voltage, induced voltage, and oil tests when applicable. FAT means the buyer or third-party inspector witnesses agreed tests at the factory.
Use the transformer FAT checklist before booking witnessed inspection.
A strong RFQ lets suppliers quote the same technical scope, so price and lead time are comparable. At minimum, include capacity, HV/LV voltage, frequency, phase, standard, cooling, vector group, impedance, tap range, accessories, tests, quantity, destination, and delivery schedule.
Transformer Academy
Start with the plain-English basics, then move into RFQ, testing, standards, cooling, and calculator tools.
Ready to Move From Learning to Specification?
Share capacity, voltage, standard, cooling type, quantity, and destination. XinHuan can help confirm missing details before quotation.