UNI-T UT225A Operating Manual page 8

(Setting of Transformer Ratio and Ratio Difference)
For example, set the transformer ratio at 150/5A and the ratio difference (error) at
3%. The set transformer ratio shall be consistent with the value on the nameplate
of the current transformer. If the actual tested ratio difference exceeds the set error,
the symbol "OL" appears on the bottom right of the LCD.
3. Transformer Ratio Testing
Refer to the on-site wire connection diagram:
Power on the tester, clamp primary and secondary circuits through CT1 and CT2
respectively, then the LCD will show current, phase identification, polarity,
transformer ratio and ratio difference converted at secondary current of 5A.
For example, set the transformer ratio at 150/5A, test in-phase positive circuit, the
primary current is 150.5A, secondary current is 5.00A, then the converted
transformer ratio is 150.5/5A and the ratio difference is 0.3%.
Since: (150.5-150)/150*100% = 0.3%
(Testing interface)
In normal testing interface, long press " " for about 2 seconds to enter angle
difference parameter interface, to view primary and secondary currents. If the
phase difference is about 0°~30° or 330°~360°, it is in-phase polarity; if the phase
difference is about 150°~210°, it is out-phase, the phase of the current lead
clamped by CT1 and CT2 are not in-phase. Long press " " again for about 2
seconds to exit angle difference parameter mode and return to testing mode.
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