3.3 Testing Miniature Line Frequency Bobbin Transformers
This miniature transformer is tested in a very similar way to the line
frequency transformer described in Section 3.2, with the following
1.Insulation tests are added to check the insulation from primary to the
safety screen and to the core.
2.The primary of this miniature transformer consists of a large number of
turns of very fine gauge wire.
Such a winding can be subject to premature breakdown in the field due to
failure of the thin enamel coating between parts of the winding.
The likelihood of field breakdown has been reduced by performing an
inter-turn stress test on the transformer.
Recommended measurements for line frequency transformers
||To ensure correct wire size has been
used and correct tension during
winding. Checks that transformer
properly installed in test fixture
|Magnetizing Current and Open Circuit Voltages
||Checks for correct core material and
core construction. Ensures that
operating on correct point on B-H
Open circuit voltage tests confirm that
windings have correct turns and have correct phasing
||Checks for weakness of interturn
||Only required on transformers used in
patient contact in medical applications
||Checks isolation between windings
||Checks safety isolation
primaries to secondaries (and screen