Casing selection test plan

1) 1 to 3 years

2) After overhaul (including major equipment overhaul) 3) If necessary

1) The insulation resistance of the main insulation should not be lower than 10000MΩ

2) The insulation resistance of the final screen to ground should not be lower than 1000MΩ

Using 2500V megohmmeter

1) 1 to 3 years

2) After overhaul (including major equipment overhaul)

3) When necessary

1) The value of tgδ(%) at 20 °C should not exceed the value in the table below;

1) Oil-paper capacitor type casing tgδ is generally not carried out
Temperature conversion, when tgδ and factory value or the last time
When the test value is significantly increased or close to the value of the left table, the relationship between tgδ and temperature and voltage should be comprehensively analyzed. When tgδ increases significantly with temperature or test
When the voltage rises from 10kV to Um/√3, the tgδ increment exceeds ±0.3% and should not continue to operate.

2) The pure porcelain sleeve below 20kV and the hydraulic sleeve connected to the transformer oil do not measure tgδ;

3) When measuring the transformer bushing tgδ, all the winding terminals connected to the tested bushing are connected together and pressurized, the other winding terminals are grounded, the last screen is connected to the bridge, and the positive wiring is measured.

Voltage level kV

20
~
35

66
~
110

220～500

Big
repair
Rear

Oil-filled

3.0

1.5

——

Oil paper capacitor

1.0

1.0

8.0

Filled type

3.0

2.5

——

Tape capacitor type

2.0

1.5

1.0

Tape type

2.5

2.0

——

2) When the insulation resistance of the end of the capacitor type casing to ground is less than 1000MΩ, the final screen to ground tgδ should be measured, and its value is not more than 2%.

3) When the capacitance value of the capacitor type bushing differs from the factory value or the previous test value by more than ±5%, the cause should be ascertained.

1) After overhaul

2) When necessary

The test voltage is 85% of the factory value.

Pure porcelain wall bushings of 35kV and below can be used with busbar insulators
Pressure resistance together