【JJG313-2010】5.3.1 Appearance inspection
Current transformers with any of the following defects must be repaired before verification:
a) No nameplate or the nameplate lacks necessary markings;
b) The terminal is missing, damaged or unmarked;
c) The transformer with multiple current ratios does not indicate the corresponding wiring method;
d) The insulation surface is damaged or damp;
e) The internal structural parts are loose;
f) Other defects that seriously affect the verification work.
【JJG314-2010】5.3.1 Appearance inspection
Voltage transformers with any of the following defects must be repaired before calibration:
a) No nameplate or the nameplate lacks necessary markings;
b) The terminal is missing, damaged or has no markings;
c) The transformer with multiple voltage ratios does not indicate the corresponding wiring method;
d) The insulation surface is damaged, the oil level or gas pressure is incorrect;
e) The internal structure is loose;
f) Other defects that seriously affect the calibration work
【Article Interpretation】If the nameplate mark, terminal, insulation surface, oil level or gas pressure indication, assembly, etc. are found to be defective or abnormal during the appearance inspection, they should be repaired before calibration.
【JJG 313-2010】5.3.2 Insulation resistance measurement
Use a 500V megohmmeter to measure the insulation resistance between each winding and between each winding and the ground, which should comply with the requirements of JB/T5472, Section 6.7; for current transformers with a rated voltage of 3kV and above, use a 2.5kV megohmmeter to measure the insulation resistance between the primary winding and the secondary winding and between the primary winding and the ground, which should not be less than 500MΩ.
【JJG314-2010】5.3.2 Insulation resistance measurement
For voltage transformers of 1kV and below, the insulation resistance between the primary winding and the secondary winding and the grounding terminal shall not be less than 20MΩ; for voltage transformers above 1kV, the insulation resistance between the primary winding and the secondary winding and the grounding terminal of the ungrounded transformer shall not be less than 10MΩ/kV, and not less than 40MΩ; the insulation resistance between the secondary winding and the grounding terminal and between the secondary windings shall not be less than 40Ω.
【Article interpretation】The requirements of Article 6.7 of JB/T 5472-1991 are: the insulation resistance between the secondary winding and the grounding terminal shall not be less than 20MΩ, and the insulation resistance between the primary winding and the secondary winding and the grounding terminal of the 0.38kV low-voltage transformer shall not be less than 40MΩ.
【JJG313-2010】5.3.3 Power frequency withstand voltage test
The test equipment and methods shall comply with the requirements of GB/T16927.1.
If no insulation damage or discharge flashover occurs during the test, the test is considered to have passed.
For the transformers used as standards in the laboratory, the power frequency withstand voltage test can be carried out according to the user's requirements during the periodic re-inspection.
【JJG314-2010】 5.3.3 Insulation strength test
The insulation strength test includes an external voltage test on the primary winding or the secondary winding.
The test voltage can be applied from the primary winding or the secondary winding.
The test voltage value is selected according to 6.7.1 of JB/T5473.
For transformers with multiple voltage ratios, the winding with the highest rated primary voltage is selected for testing.
The test equipment and methods shall comply with the requirements of GB/T16927.1.
If no insulation damage or discharge flashover occurs during the test, the test is considered to have passed.
For voltage transformers for special purposes, insulation strength tests can be carried out according to user requirements.
For transformers used as standards in the laboratory, power frequency voltage tests can be carried out according to user requirements during periodic re-inspections.
【Article Interpretation】 The power frequency test voltage between the primary winding of the current transformer and the secondary winding and the grounding terminal is shown in Table 2-1. The test time is 1min.
After the insulation resistance measurement of 0.38kV low-voltage current transformer is qualified, the power frequency withstand voltage test can be omitted.
Note that the power frequency withstand voltage test is a mandatory test item during the first calibration, and it is an optional test item during subsequent calibration and inspection during use.
