Buying a transformer from overseas moves the point of inspection a long way from the point of use. Whatever is checked before shipment is the last chance to catch a problem while it is still the supplier’s to fix, which makes the test regime worth understanding.
Routine, type and special tests
Tests fall into three groups. Routine tests are carried out on every unit before it leaves the works. Type tests are done once on a design to prove it meets the standard. Special tests are done on request for a particular project.
Routine tests are what protect you on the unit you actually bought, so make sure the report you receive is for your serial number, not a generic sheet for the series.
What the routine tests normally cover
For a dry type transformer to IEC 60076-11, a typical routine set covers winding resistance, voltage ratio and vector group, insulation resistance, and an applied and induced voltage withstand test. Partial discharge measurement is common for dry type units, because the insulation is exposed to air and moisture in a way an oil tank is not.
Confirm the exact list against the standard you are buying to, and ask for the figures, not just a pass stamp.
Third-party inspection
Where the order value or the project rules justify it, a third-party inspection house can witness the tests on your behalf. Decide early whether you want a witnessed test or a remote review of the report, because a witnessed test has to be scheduled before the unit is packed.
The documents to collect
Ask for the routine test report for the serial number, the outline drawing, the nameplate details, the packing list and a statement of the standard the unit complies with — IEC 60076 or ANSI/IEEE C57.12, as applicable to your market. If the project needs certificates or type-test evidence, request them at the enquiry stage rather than after shipment.
Checks before the container closes
Before packing, confirm that the nameplate matches the purchase order on rating, voltages, vector group and cooling class, that the enclosure and paint are undamaged, and that the accessories on the order are all present and correctly fitted. A missing sensor or a mismatched nameplate is far easier to fix in the works than on site.
Watch the quiet gaps
The common misses are a test report that is not tied to the serial number, a sound level that was assumed rather than guaranteed, and a nameplate that does not match the order. Each is avoidable with one clear line in the specification.
Hebei Youge provides routine test reports, drawings and documentation with every transformer and can arrange witnessed testing where a project requires it. Send the specification and we will confirm what is included.