The insulation dielectric performance test of instrument transformers shall comply with the following provisions:
1. The performance of insulating oil shall meet the specified requirements;
2. For instrument transformers filled with SF₆ gas, sampling and testing shall be carried out after standing for 24h. The moisture content of the gas shall not be greater than 250 μL/L (volume percentage at 20℃); for the 750kV voltage level, the moisture content of the gas shall not be greater than 200 μL/L;
3. For oil-immersed instrument transformers with a voltage level above 66kV, when there is doubt about the insulation performance, chromatographic analysis of dissolved gases in oil shall be conducted. The total hydrocarbon content of dissolved gas components in oil shall not exceed 10 μL/L, the H₂ content shall not exceed 100 μL/L, and the C₂H₂ content shall not exceed 0.1 μL/L.
The measurement of winding DC resistance in the handover test of instrument transformers shall comply with the following provisions:
1. Voltage transformers: The measured value of the DC resistance of the primary winding shall not differ by more than 10% from the factory value converted to the same temperature. The measured value of the DC resistance of the secondary winding shall not differ by more than 15% from the factory value converted to the same temperature.
2. Current transformers: The difference between the DC resistance of the windings of current transformers of the same model, specification and batch and the average value shall not exceed 10%. When the primary winding has series or parallel connection modes, the DC resistance measurement of the primary winding of the current transformer shall be carried out under the normal operation mode, or the DC resistance of the primary winding under both connection modes shall be measured simultaneously. The difference between the DC resistances of the single-section primary windings of inverted current transformers shall not exceed 30%. When in doubt, the applied measuring current shall be increased, and the measuring current (DC value) shall not exceed 50% of the rated current (root mean square value).
The connection winding group and polarity of the instrument transformer shall meet the design requirements and be consistent with the nameplate and marks.
The error and transformation ratio measurement in the handover test of instrument transformers shall comply with the following provisions:
1. Instrument transformers used for gateway metering (including current transformers, voltage transformers and combined transformers) shall be subjected to error measurement;
2. For instrument transformers used for non-gateway metering, the transformation ratio of the instrument transformer shall be checked and shall be consistent with the manufacturer’s nameplate value. For multi-tap instrument transformers, only the transformation ratio of the used tap may be checked.
Post time: Apr-03-2026