How long after installation can a current transformer be energized and put into operation?

After installation, a current transformer must be energized and put into operation only after all acceptance tests have been completed and confirmed to be qualified. This process is usually carried out immediately after installation and must be completed before energization; there can be no delay.

Specifically:

All critical tests (such as insulation resistance measurement, turns ratio and polarity check, AC withstand voltage test, etc.) must be completed after installation and before formal energization.

For 110kV and above oil-immersed transformers, if they are not energized immediately after installation, there are strict requirements for the settling time: 110kV equipment must be settling for no less than 24 hours, 220kV for no less than 48 hours, and 330kV and above for no less than 72 hours before withstand voltage testing and commissioning can be carried out.

Transformers installed for emergency repairs also need to have a settling time; for 110~220kV, it should be greater than 24 hours.

Therefore, whether power can be supplied depends not on "how long has passed since installation," but on whether the testing has been completed, whether the settling period has met the standards, and whether the acceptance test has been passed. Power supply is only permitted if all conditions are met.