Why Three Families Exist At All
A bushing does the same job everywhere, but the dimensional pattern, the test values and the part designation grew up separately in Germany, across Europe and in North America. A terminal board drilled to one pattern will not take another, which is why the standard on the drawing matters more than the electrical rating when you are ordering a replacement.
The DIN Families
DIN specifications are no longer live standards but are still utilised widely by the transformer and distribution industry. DIN 42530 covers the 1kV low voltage series, DIN 42539 the 3kV series, and DIN 42531 the high voltage NF patterns. Bushings here are also manufactured to DIN 52432, 42533, 42534 and 40680. The NF number identifies the voltage class: 10NF is 10kV, 20NF is 20kV and 30NF is 36kV.
DIN 42531 30NF250A Transformer Bushing
The EN Families
EN 50180 and EN 50386 are the current specification set. Together they cover ratings from 1kV through 52kV and up to 12500A, with a wide variety of creepage distances for different environmental conditions. EN 50386 extends the low voltage table further than DIN 42530 does, reaching 4000A at 85mm creepage. Construction type variants such as EN 50180 Type 3 are ordered by type, not just by rating.
EN 50180 24kV 250A Porcelain Transformer Bushing
The ANSI Family
ANSI transformer bushings are specified by model, with published height, arcing distance, creep distance, shed count and weight. ANSI-15/50 is 485mm tall with 310mm creep across 5 single umbrella sheds at 2.8kg, ANSI-18/50 is 541mm with 480mm creep across 8 sheds at 3.5kg, and ANSI-27/50 is 722mm with 830mm creep across 12 sheds at 5kg. The low voltage side uses imperial threaded rods with eyebolt and flat connectors rather than metric stems.
Threaded ANSI 18kV Transformer Bushing ANSI-18/50
What Testing Applies Across All Of Them
Regardless of which family the dimensional detail comes from, all outdoor bushings are manufactured and tested in accordance with IEC 60137. That is the common ground between the three, and it is the reference to quote when a specification asks for test evidence.
DIN 42531 10NF250A Transformer Bushing
How To Decide What To Order
Order against the standard printed on your drawing, not against the electrical rating alone. If the drawing is lost, send the installed bushing or a photograph with the tank hole size and stem thread and the pattern can be identified from those two figures in most cases.
