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At the Transformer switch on, often the primaryside fuse trips. In this case a 100VA, 230V Transformer switch on blows this 0,8A fuse. Particularly Transformers with a toroidal shaped core, produce a very high Inrush current peak. They cannot be fusable with fuses also with double or triple of the nominal current value.  A Transformer-Switch-Relay, -TSR- avoids Inrush current peaks, and allow fusing with nominal current values. Frequently switching is possible.

At the other hand, also short time Voltage dips, can drive a transformer core into saturation. Depending of the phase angle of the dip to the sine wave of the grid voltage, a big inrush current peak can occur. Until now normally inrush current limiters cannot deal with this fast acting voltage dip problem, because their bridge relays is not to bring fast enough in an open state. And then after the dip, the transformer saturation produce an inrush and this trips the fuse. Why this happens, you can learn here, see "Important to know about Inrush current avoiding, -Speech".

With a Transformer switching relay, -TSR-, there exist no such voltage dip problem, because it can recognise the voltage dip and can react fast enough to protect the transformer from saturation.

Medical electric equipments must resist the test following EN 610004-11-, -this is a Test with a voltage dip of an half wave, inside the EN 60601-1-2 medical Norm.  With a  Transformer switching relay, with the Option "half wave failure recognition", who is installed between the power line input and the Transformer input, the equipment can surely pass this test.

Transformerphysic can understanding very easy. It is demonstrated with voltage and current measures and with the explanation of the function of the TSR switch-on-procedure.