For single phase Transformers you can use two diffent types of Transformer Switching relays: TSRL and TSRLF.
TSRL means:
Transformer Switching Relay Low-cost. = all in one unit, thyrister is bridged internally, need no additional elements.
TSRLF means:
Transformer Switching relay Low-cost Fast-switching. = Modul to control an external random switching solid state relay or a thyristor modul in the TSR manner. TSRLF can control en external bypass contactor. This is a TSRLF with Option: with control relay to switch an external Bypass contactor on and off, in the correct time window.