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7.3 Pre-commissioning test
7.3.1 Voltage ratio test: Measure the voltage ratio of the winding under all taps and the connection group. The
allowable deviation of rated tap voltage ratio shall not exceed
±
0.5%, except for special transformers.
7.3.2 Wingding resistance test: Measure the DC resistance of the winding at all taps and records the winding
temperature.
7.3.3 Insulation resistance test: Measure the insulation resistance values of the windings and cores (as shown in the
table below) and record ambient temperature and humidity.
Typically, the insulation resistance is measured at ambient temperature of-25 º C ~ 50 º C, humidity ≤ 90%, and
the insulation resistance of the transformer would decrease in humid environment. If the transformer suffers from
dampness, the transformer can be dried. If the insulation resistance is not less than 2 M
Ω
, a voltage can be applied to
the low-voltage side of the transformer and the transformer can be dried by no-load heating. If the insulation resistance
value is less than 2 M
Ω
, it can be dried by air drying or baking with heat lamp.
7.3.4 Applied withstand voltage test: The withstand voltage strength of the transformer is tested. The on-site tested
withstand voltage value is 80% of the factory test voltage value. The factory test withstand voltage value can be
shown in the factory test report and nameplate.
Test position
Test equipment
Test value requirements
High voltage terminal -
low voltage te ground
2500 V Megohmmeter
≥100 M
Ω
Low voltage terminal -
High voltage te ground
2500 V Megohmmeter
≥100 M
Ω
High voltage te low voltage terminal
- ground
2500 V Megohmmeter
≥100 M
Ω
Iron core - ground
2500 V Megohmmeter
≥10 M
Ω
7. Commissioning
Note:
•
After testing the insulation resistance of the iron core-ground, it is necessary to restore the connection of the grounding strap.