C. Theory of Operation
72A-2570-01 Rev. K 07/2011 C-5
Transformer
SFRA tests measure only the RLC network of the transformer. To maintain
consistency and repeatability of measurements, make sure that all terminals
not under test are isolated and floating. To maintain a balanced and
symmetrical approach, where a delta winding is completed and grounded
external to the transformer tank, the delta should be complete but floating.
Such windings are frequently used for regulation; where such windings are
grounded internal to the tank, it is necessary to leave that ground in place —
but we should expect asymmetry in the results.
We could measure a frequency response with the remaining terminals
grounded, but it could not be compared to a response measured with floating
terminals, which would display a different RLC response.
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