Test items, cycles, and requirements for dry type current transformers

Insulation resistance of windings and end screens ① 35kV and above: 3 years; 10kV: 6 years

② After major maintenance

③ If necessary, ① The insulation resistance between the primary winding and the end screen, ground, and between each secondary winding and ground should not show significant changes compared to the factory values and previous data. Generally not less than 70% of the factory value or initial value

② The insulation resistance of the end screen of capacitive current transformers should not be less than 1000M Ω ① A 2500V insulation resistance tester should be used

② If necessary, such as when a fault is suspected 2

tan δ And capacitance of 35kV and above:

① 3 years

② After major maintenance

③ If necessary, ① If the difference between the main insulation capacitance and the initial or factory value exceeds ± 5%, the cause should be identified

② Refer to the manufacturer's technical conditions for testing. If there is no manufacturer's technical conditions, the main insulation tan δ It should not exceed 0.5% and there should be no significant changes compared to previous years' data. ① Only capacitance type transformers of 35kV and above should be tested

. ② When tan δ When there is a significant increase in the value compared to the factory value or the previous test value, a comprehensive analysis of tan should be conducted δ The relationship with temperature and voltage, when tan δ With significant changes in temperature or test voltage from 10kV to Um/√ 3, tan δ If the absolute value of the change exceeds ± 0.3%, it should not continue to operate.

③ For capacitive transformers that meet the testing conditions, live testing can be used δ And capacitance replacement 3

live test tan δ And capacitance: ① One month after production

② One year

③ After major maintenance

④ If necessary, ① The in-phase comparison method can be used, and the judgment standard is:

- The difference in dielectric loss measurement values of in-phase equipment (tan δ X tan δ N) Compared with the difference between the initial measurement value, the absolute value of the variation range does not exceed ± 0.3%, and the capacitance ratio (Cx/CN) does not exceed ± 5% compared to the initial measurement capacitance ratio.

- The dielectric loss measurement value of the same model of equipment (tan δ X tan δ N) Not exceeding ± 0.3%

② When using other testing methods, operating rules can be formulated according to the actual situation, only for capacitive current transformers with installed live testing signal sampling units. When exceeding the requirements, the following should be done:

① Identify the cause

② Shorten the test cycle

③ If necessary, cut off the power for retesting.

AC withstand voltage test of 35kV and above: if necessary

10kV: 6 years. ① The primary winding should be tested at 0.8 times the factory value, and the withstand voltage test of 10kV current transformer should be conducted at 35kV.

② The power frequency withstand voltage test between the secondary windings and the end screen to ground should be 2kV, and a 2500V insulation resistance tester can be used to replace it if necessary, For example, when there is suspicion of insulation failure, 5

Partial discharge test for 110kV and above: if necessary, at a voltage of 1.2Um/√ 3, the apparent discharge amount should not exceed 50pC. If necessary, for example, when there is suspicion of insulation performance, 6

The ratio inspection of each tap should be conducted if necessary. ① It should be consistent with the nameplate markings.

② The ratio difference and phase difference should not show significant changes compared to the manufacturer's test values, And comply with the level regulations. ① For the cost winding of the metering meter, the ratio difference and phase difference should be measured.

② If necessary, such as when changing the ratio tap operation.

When necessary, check the excitation characteristic curve. ① Compared with the characteristic curve of similar transformers or the characteristic curve provided by the manufacturer, there should be no significant difference.

② Multiple tap current transformers can be measured using tap or maximum tap when necessary, For example, when there are requirements for relay protection, 8

infrared temperature measurement shall be carried out for 1 year according to DL/T664-1999 using an infrared thermal imager for measurement