【JJG313-2010】5.3.6 Error measurement
5.3.6.1 When measuring the error, appropriate standard instruments and measuring equipment should be selected according to the accuracy level of the current transformer under test and the requirements of Article 5.1 of this regulation.
The wiring of the calibration circuit should comply with the following provisions: the polarity end of the primary winding of the standard transformer is connected to the polarity end of the primary winding of the transformer under test, and the polarity end of the secondary winding of the standard transformer is connected to the polarity end of the secondary winding of the transformer under test; the secondary polarity end of the current transformer is connected to the polarity end of the differential current loop of the error measuring device, and the grounding end of the secondary measurement loop is connected to the non-polarity end of the differential current loop.
The potential at both ends of the differential current loop should be as equal as possible and equal to the ground potential.
In order to avoid leakage of the measured current from the primary polarity end, the primary polarity end should be as close to the ground potential as possible.
When testing the current range with a rated primary current greater than or equal to 5A, the secondary circuit can be grounded at the non-polarity end of the current transformer being tested; when testing the current range with a rated primary current less than 5A and an accuracy higher than 0.05, the primary circuit should be indirectly grounded through a symmetrical branch; the standard instrument or current transformer being tested with a primary compensation winding should be grounded through the winding.
【JJG 314-2010】 5.3.5 Basic error measurement
The basic error of voltage transformer can be measured by comparison method using standard voltage transformer, voltage ratio standard or capacitive voltage ratio device.
【Article interpretation】 The primary polarity end and secondary polarity end of the standard and tested current transformer are connected. First, the polarity ends of the two current transformers are at the same potential.
The secondary polarity end is grounded through the differential current loop of the tester.
The voltage drop of the differential current loop is very small.
The secondary polarity end is at ground potential.
The primary winding is directly grounded through the non-polarity end or indirectly grounded through the symmetrical branch or the primary compensation winding to avoid the leakage current of the polarity end causing the error of the calibration.
Secondly, the error of the standard current transformer can be accurately transmitted, that is, the polarity ends of the standard and tested current transformers are at ground potential, and the internal leakage of the transformer is the same.
In this way, as long as the secondary load of the standard and tested current transformers is the same in the calibration circuit, their errors are exactly the same.
