When a transformer is de-energized, the core retains some level of residual magnetism, known as remanent flux. This remanent flux can significantly impact the transformer’s performance upon re-energization.
Here’s how it affects the process- :Effects of Remanent Flux
1. Inrush Current:-
When a transformer is re-energized, if the voltage waveform coincides with the polarity and level of the remanent flux, a large inrush current can occur. This inrush current can be several times higher than the transformer’s rated current and can cause mechanical stress, insulation damage, and maloperation of protection devices.
2. Core Saturation:-
If the remanent flux is high, it can push the core into saturation quickly when re-energized. Saturation of the core reduces its inductive properties, leading to higher magnetizing currents.