1. The variation preheats the DC current transformer, rises to the rated current value for 10 minutes, and then rapidly drops to any point in the measuring range, the error variation between the ascending and descending values shall not be greater than 1/3 of the error limit corresponding to the accuracy grade. During the test, the error should not exceed the error limit corresponding to the accuracy grade. 

2. The DC current transformer is preheated by short-term stability, within the environmental conditions specified in its technical conditions to ensure accuracy, and within the rated working current of 30 minutes, the variation of the error should be greater than 1/3 of the error limit corresponding to the accuracy grade. During the test, the error should not exceed the error limit corresponding to the accuracy grade. 

3. The variation of the two adjacent calibration errors of the periodic stability DC current transformer shall not be greater than 1/2 of its allowable error.