what is inrush current in transformer?

Answer Posted / malkit

When a transformer is first energized a transient current
up to 10 to 50 times larger than the rated transformer
current can flow for several cycles. This happens when the
primary winding is connected around the zero-crossing of
the primary voltage. For large transformers, inrush current
can last for several seconds. Toroid transformers can have
up to 80 times larger inrush, because the remanent
magnetism is nearly as high as the saturation magnetism at
the "knee" of the hysteresis loop. This is caused because
the transformer will always have some residual flux density
and when the transformer is reenergized the incoming flux
will add to the already existing flux which will cause the
transformer to move into saturation. Then only the
resistance of the primary side windings and the power line
are limiting the current.

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