How does VOC and TR accuracy vary with frequency?
Open circuit voltage (VOC) measurements are the preferred tests for line frequency transformers, designed to operate over the full extent of the B-H curve, including the non-linear regions and checks for the correct numbers of turns on each winding.
Turns ratio (TR) is the preferred test for higher frequency signal, pulse and switched mode power transformers, where the normal operating conditions require only small excursions of the B-H curve, never extending beyond the linear regions.
TR is therefore considered to be relevant to higher frequency testing, VOC for lower frequency laminates.
Please see attachment for the full accuracy specifications for TR and VOC tests.
The formula terms (AC) that define accuracy vs frequency are as follows:
TR, 20Hz to 3MHz (AC = 0.1% + (0.00003% x FM)
VOC, 20Hz to 1500Hz (AC = 0.03% + (0.001% x FM )
Tests were designed with this consideration in mind and accuracy reflects this design consideration.