The Siemens 3UG3511-1AV50 is a 22.5 mm monitoring relay that watches for phase sequence and phase failure on three-phase supplies from 3x400 V to 3x690 V AC, 50/60 Hz. It carries one changeover contact and terminates via screw connection.
The voltage range — 3x400…3x690 V AC — covers standard European 400 V three-phase networks up to 690 V industrial mains. The 50/60 Hz rating means it works on either frequency without adjustment. A single changeover contact (SPDT) is enough to signal a fault to a PLC digital input or drop out a contactor coil; if you need two isolated signal paths, you'll need an auxiliary relay downstream.