Section 1 General Rules

Norms of acceptance tests. Measuring current transformers

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.8.17. 1. Measurement of insulation resistance.

Measuring the resistance of the main insulation of current transformers, the insulation of the measuring capacitor and the terminal of the last lining of the paper-oil insulation of the capacitor type is carried out with a 2500 V megohmmeter.

The resistance of the secondary windings and intermediate windings of cascade current transformers relative to the base is measured with a 1000 V megohmmeter.

The measured insulation resistance values ​​must be no less than those given in table. 1.8.13.

For cascade current transformers, the insulation resistance is measured for the current transformer as a whole. If the results of such measurements are unsatisfactory, the insulation resistance is additionally measured in stages.

2. Measurement of tg δ insulation.

Measurements of tg δ of current transformers with main paper-oil insulation are carried out at a voltage of 10 kV.

The measured values, normalized to a temperature of 20 ºС, should be no more than those indicated in the table. 1.8.14.

For cascade current transformers, tg δ of the main insulation is measured for the current transformer as a whole. If the results of such measurements tg δ of the main insulation are unsatisfactory, an additional measurement is carried out in stages.

3. Test with increased voltage of industrial frequency 50 Hz.

3.1. High voltage test of the main insulation.

The test voltage values ​​of the main insulation are given in table. 1.8.16. Test duration for current transformers is 1 min.

It is allowed to test current transformers together with the busbar. Current transformers with voltages over 35 kV are not subject to increased voltage tests.

3.2. High voltage test of insulation of secondary windings.

The value of the test voltage for insulating the secondary windings together with the circuits connected to them is assumed to be 1 kV.

The duration of the test voltage application is 1 min.

4. Removal of magnetization characteristics.

The characteristic is removed by increasing the voltage on one of the secondary windings until saturation begins, but not higher than 1800 V.

If the windings have branches, the characteristic is taken at the working branch.

The taken characteristic is compared with the typical magnetization characteristic or with the magnetization characteristics of serviceable current transformers of the same type as those being tested.

Differences from the values ​​measured at the manufacturer or from those measured on a working current transformer of the same type as the one being tested should not exceed 10%.

Only three control points are allowed to be taken.

5. Measurement of the transformation ratio.

The deviation of the measured coefficient from that indicated in the passport or from that measured on a working current transformer of the same type as the one being tested should not exceed 2%.

6. Measurement of resistance of secondary windings to direct current.

The measurement is carried out at current transformers for a voltage of 110 kV and above.

The deviation of the measured DC winding resistance from the rated value or from that measured on other phases should not exceed 2%. When comparing the measured value with the nameplate data, the measured resistance value must be adjusted to the factory temperature. When comparing with other phases, measurements on all phases must be carried out at the same temperature.

7. Testing of transformer oil.

When commissioning current transformers, transformer oil must be tested in accordance with the requirements of Table. 1.8.33 paragraphs 1-6, and for sealed ones according to paragraph 10.

For oil-filled cascade current transformers, the condition of the transformer oil in each stage is assessed according to standards corresponding to the operating voltage of the stage.

8. Testing of built-in current transformers.

Produced according to paragraphs 1, 3.2, 4-6. The insulation resistance of built-in current transformers is measured with a megohmmeter for a voltage of 1000 V.

The measured insulation resistance without secondary circuits must be at least 10 MΩ.

It is possible to measure the insulation resistance of built-in current transformers together with secondary circuits. The measured insulation resistance must be at least 1 MΩ.

Table 1.8.13. Insulation resistance of cascade current transformers

* The insulation resistances of the secondary windings are given: without brackets - with the secondary circuits disconnected, in brackets - with the secondary circuits connected.

Table 1.8.14. Values ​​of tgδ of the main insulation of current transformers

See other articles Section Rules for the installation of electrical installations (PUE).

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