The 1.5SMC27AT3G is listed as Obsolete by Littelfuse.
Zener TVS — 1500W peak pulse in DO-214AB
Breakdown occurs at a minimum of 25.7V, and the clamping voltage is held to 37.5V maximum at the rated 40A peak pulse current. This 37.5V clamp ceiling is the figure a downstream IC's absolute-maximum input voltage must stay above — if the protected rail sees a surge, the TVS holds it under that limit.
No power line protection — signal and DC bus only
Being a unidirectional device, it clamps only one polarity — the cathode is tied to the protected rail, and the anode to ground. For AC or bidirectional lines, two devices back-to-back or a bidirectional TVS would be needed.