Section 1 General Rules

Norms of acceptance tests. Power transformers, autotransformers, oil reactors and grounding arc quenching reactors (arc coils)

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

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1.8.16. Oil-filled transformers up to 630 kVA are tested in accordance with paragraphs 1, 2 (insulation resistance only), 11-14.

Oil-filled transformers with a power of up to 1,6 MVA are tested according to clauses 1, 2, 4, 9, 11-14.

Oil-filled transformers with a power of more than 1,6 MVA, as well as auxiliary transformers of power plants, regardless of power, are tested in full, provided for in this paragraph.

Dry and filled with non-combustible liquid dielectric transformers of all capacities are tested according to clauses 1-7, 12, 14.

1. Determining the conditions for switching on transformers.

Should be produced in accordance with the manufacturer's instructions.

2. Measurement of insulation characteristics.

For transformers with voltage up to 35 kV inclusively with a power up to 10 MVA and arc-suppressing reactors, the insulation resistance of the windings must not be lower than the following values:

The insulation resistance of dry transformers at a temperature of 20-30 ºС should be for windings with a rated voltage:

• up to 1 kV inclusive - not less than 100 MOhm;
• more than 1 kV up to 6 kV - not less than 300 MΩ;
• more than 6 kV - not less than 500 MΩ.

For other transformers, the insulation resistance, adjusted to the measurement temperature at the factory, must be at least 50% of the original value.

The values ​​of the dielectric loss tangent (tg δ), reduced to the measurement temperature at the manufacturer's plant, should not deviate from the initial values ​​by more than 50%.

Measurement of insulation resistance and tg δ should be carried out at a winding temperature not lower than:

10 ºС - for transformers with voltage up to 150 kV;

20 ºС - for transformers with a voltage of 220-750 kV.

Measurement of tg δ for transformers up to 1600 kVA is not necessary.

Measurement of the insulation resistance of accessible tie rods, bandages, yoke half bandages and pressing rings relative to active steel and electrostatic screens, relative to windings and magnetic circuit is carried out in case of inspection of the active part. The measured values ​​must be at least 2 MΩ, and the insulation of the yoke beams must be at least 0,5 MΩ. Measurements are made with a megohmmeter for a voltage of 1000 V.

3. Power frequency overvoltage test:

a) insulation of the windings together with the inputs. Test voltages are given in table. 1.8.12. The duration of application of the normalized test voltage is 1 min.

Testing with increased voltage of industrial frequency of the insulation of the windings of oil-filled transformers is not necessary.

Testing with increased voltage of the industrial frequency of the insulation of the windings of dry transformers is mandatory and is carried out according to the norms of Table. 1.8.12 for devices with lightweight insulation.

Imported transformers are allowed to be tested with the voltages indicated in Table. 1.8.12, only if they do not exceed the voltage with which this transformer was tested at the factory.

The test voltage of grounding reactors for voltage up to 35 kV is similar to those given for transformers of the corresponding class;

b) insulation of accessible tie rods, pressure rings and yokes. The test should be carried out in case of inspection of the active part. Test voltage 1 kV. The duration of application of the normalized test voltage is 1 min.

4. Measurement of winding resistance to direct current.

Produced on all branches. The resistance should differ by no more than 2% from the resistance obtained on the same branch of other phases, or from the manufacturer's data.

The resistance value of the windings of single-phase transformers after temperature recalculation should not differ by more than 5% from the initial values.

5. Checking the transformation ratio.

Produced at all stages of switching. The transformation ratio must differ by no more than 2% from the values ​​obtained on the same branch on other phases, or from the manufacturer's data. For transformers with on-load tap-changers, the difference between the transformation ratios must not exceed the value of the regulation step.

6. Checking the connection group of three-phase transformers and the polarity of the outputs of single-phase transformers.

Produced if there are no passport data or there are doubts about the reliability of these data. The group of connections must correspond to the passport data and designations on the label.

7. Measurement of no-load losses.

Measurements are made for transformers with a capacity of 1000 kVA or more at a voltage supplied to the low voltage winding equal to that specified in the factory test report (passport), but not more than 380 V. For three-phase transformers, no-load losses are measured with single-phase excitation according to the schemes used at the factory.

For three-phase transformers, during commissioning, the ratio of losses in different phases should not differ from the ratios given in the factory test report (passport) by more than 5%.

For single-phase transformers, during commissioning, the difference between the measured loss values ​​and the initial ones should not exceed 10%.

7.1. Measurement of short circuit resistance (Zк) of the transformer.

The measurement is made for transformers 125 MB·A and more.

For transformers with a voltage regulation device under load, Zk is measured on the main and both extreme branches.

Zk values ​​should not exceed the value determined by the short circuit voltage (uk) of the transformer on the main branch by more than 5%.

8. Checking the operation of the switching device.

Manufactured in accordance with the manufacturer's instructions.

9. Tank test with radiators.

All transformers are tested, except for hermetically sealed and without an expander. The test is made:

• for transformers with voltage up to 35 kV inclusive - by hydraulic pressure of the oil column, the height of which above the level of the filled expander is 0,6 m, except for transformers with corrugated tanks and lamellar radiators, for which the height of the oil column is assumed to be 0,3 m;
• for transformers with film oil protection - by creating an excess air pressure of 10 kPa inside the flexible shell;
• for other transformers - by creating an excess pressure of nitrogen or dry air of 10 kPa in the above-oil space of the expander.

The duration of the test in all cases is at least 3 hours. The temperature of the oil in the tank when testing transformers with voltage up to 150 kV inclusive is not lower than 10 ºС, the rest is not lower than 20 ºС.

The transformer is considered to be oil-tight if no oil leakage is detected by inspection after the test.

10. Checking cooling devices.

The mode of start-up and operation of cooling devices must comply with the manufacturer's instructions.

11. Checking the means of protecting the oil.

Manufactured in accordance with the manufacturer's instructions.

12. Phasing of transformers.

There must be phase matching.

13. Testing of transformer oil.

Fresh oil before pouring newly commissioned transformers arriving without oil must be tested according to the indicators of paragraphs 1-6, 7-12 of Table 1.8.33.

For transformers with voltage up to 35 kV, it is recommended to test the oil according to the indicators of items 1-7 of Table 1.8.33, it is allowed not to test according to items 3, 6 and 7 of Table 1.8.33.

For transformers with a voltage of 110 kV and above, the oil is tested according to clauses 1-7 of Table 1.8.33, and for transformers with film oil protection, additionally according to clause 10.

For transformers with an on-load tap-changer, the oil from the voltage regulator contactor tank under load is tested in accordance with the on-load tap-changer manufacturer's instructions.

Oil samples are not taken from sealed transformers.

For transformers with a voltage of 110 kV and above, as well as block transformers for auxiliary needs, it is recommended to carry out a chromatographic analysis of gases dissolved in oil.

Oil from transformers arriving for installation with oil in the presence of factory test indicators that meet the standards, carried out no more than 6 months before the transformer is put into operation, is allowed to be tested only according to the indicators of paragraphs 1 and 2 of Table 1.8.33.

For transformers with a power of up to 630 kVA, it is allowed to check the oil only according to paragraphs 1 and 2 (visually) of Table 1.8.33.

14. Test by switching on with a push at rated voltage.

In the process of switching the transformer on 3-5 times at rated voltage, there should be no phenomena indicating an unsatisfactory condition of the transformer.

Transformers mounted according to the block diagram with a generator are recommended to be connected to the network by raising the voltage from zero.

15. Testing of inputs.

Should be produced in accordance with 1.8.33.

16. Testing of built-in current transformers.

Should be produced in accordance with 1.8.17.

Table 1.8.12. Test voltage of industrial frequency of internal insulation of power oil-filled transformers and reactors with normal insulation and transformers with lightweight insulation (dry and oil-filled)

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

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