(1) Connect the secondary load.
The current transformer should be connected to the specified upper or lower load.
Note that the lower load required by the regulations is 3.75VA (rated current 5A) and 1VA (rated current 1A).
If the user has requirements, the lower load is 1/4 of the rated load.
(2) Select the current ratio.
Unless the user has requirements, the current transformer is only tested for the ratio actually used.
If the user plans to change to another ratio during the calibration period, the user should ask the calibration agency to increase the ratio to be tested before the calibration.
(3) Select the current calibration point.
The current calibration point of the current transformer is selected according to Table 9.
When large current transformers (rated primary current 3kA and above) are tested in subsequent calibration and use, with the approval of the superior metrology administrative department, it is allowed to merge the 100% and 120% rated primary current calibration points into the actual maximum primary current point.
(4) Magnetic saturation margin test.
At present, the current range of the current transformer tester and load box is designed to be up to 120% of the rated current.
Therefore, the error at the 150% point or 200% point needs to be measured by extrapolation measurement method.
If the selected extrapolation starting point is not 20% of the rated current, but m%, the error at 150% of the rated current can be measured according to the following steps:
Assume that the rated secondary load of the current transformer is Z1, the secondary winding resistance and leakage reactance are Z2, and the error of the current transformer can be measured under the secondary load Z1, the current percentage point m%, and the secondary load 2Z1+Z2, the current percentage point 0.5m%, respectively, to obtain , 5 and force, 8.
Then measure the error of the current transformer under the secondary load (150/m)Z1+(150/m-1)Z2, the current percentage point m%.
