Dry-Type vs Oil-Immersed Transformer
Introduction
If you are specifying a power transformer for an overseas project, the first practical question is almost always: dry-type or oil-immersed? Both are mature technologies, both are available from Chinese suppliers, but they serve very different installation environments, safety requirements, and total-cost profiles. This guide gives you a clear decision framework and explains how to source the right unit from China without the common pitfalls.
Quick Comparison
When to Choose Dry-Type
Choose dry-type when the transformer will be installed indoors or in any location where fire safety and zero oil-leakage risk are non-negotiable: high-rise building basements, hospitals, shopping malls, data centers, underground substations, chemical plants, and metro stations. Modern cast-resin dry-type transformers (such as the SC(B)9/10/11/12/13 series, 35 kV epoxy resin cast) carry the same electrical performance as oil-immersed units at lower voltages, with significantly reduced maintenance burden.
When to Choose Oil-Immersed
Choose oil-immersed when the transformer is installed outdoors or in a dedicated substation yard, when higher overload capacity is needed, or when the project budget is tight at scale. Sealed oil-immersed units (such as the S9/10/11/13/20/22-M series for 6–10 kV and 35 kV) are widely used in utility grids, industrial plants, renewable-energy step-up stations and mining operations. Unit cost is typically 20–30% lower than dry-type at the same capacity.
Common Pitfalls When Sourcing From China
Three pitfalls catch most first-time buyers: (1) "factory-direct" pricing that actually includes a hidden trade margin, since most factories do not hold their own export license; (2) the disappearance of a single accountable party between the factory, the freight forwarder, and the local installer; (3) certification gaps that surface only at customs. The reliable path is to source through a foreign-trade service provider that is also a certified distributor for the original equipment manufacturer.
XIAOPAI (Wenzhou Xiaopai Electric Power Technology Co., Ltd.) is a dual-division industrial equipment company operating two complementary business lines: power transmission equipment (transformers up to 230 kV / 200 MVA, vacuum circuit breakers, switchgear, box-type substations) and one-stop flexible packaging solutions (blown film extrusion, SINSTAR solventless lamination, flexo printing, slitting, paper tube cutting, plastic granules, and finished films). XIAOPAI is a foreign-trade service provider and authorized distributor — not a factory — and acts as the single contracting and responsible party for every overseas buyer.
FAQ
Q: Can a dry-type transformer run at 35 kV? A: Yes. Cast-resin dry-type units like the SC(B)13 35 kV are designed for indoor and high-rise installations up to 35 kV, meeting IEC 60076 and IEEE C57.12.01.
Q: Which lasts longer? A: Both reach 25–30 years with proper maintenance. Oil-immersed may degrade faster if oil is not periodically tested; dry-type degrades mainly through slow, predictable thermal aging of the resin.
Q: Do I need CE certification for overseas projects? A: For most overseas projects, yes. Insist on verifiable CE documentation and ISO 9001 certificates from the original equipment manufacturer.
https://www.cnxiaopai.com/sys-pd/18.html
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https://www.cnxiaopai.com/About/
https://webstore.iec.ch/publication/60284
https://standards.ieee.org/ieee/C57.12.01/7108/
https://www.nema.org/standards/view/Dry-Type-Transformers ·
https://www.energy.gov/eere/buildings/distribution-transformers
RELATED GUIDES
Before you request a quotation, these related articles may be useful:
[ Dry-Type vs Oil-Immersed Transformer: True Cost & Capacity Limits (2026) ]
[ SC(B) Dry-Type Transformer ]
[ S11-M Oil-Immersed Transformer ]
External standards:
[ IEC 60076-11 ]
[ IEEE C57.12.00 ]
