6 VOLTAGE TRANSFORMER SUPERVISIONThe Voltage Transformer Supervision (VTS) function detects failure of the AC voltage inputs to the IED. Ifthe IED misinterprets this as a failure of the actual phase voltages on the power system, it could result inunecessary tripping of a circuit breaker. To prevent this, the VTS detects voltage input failures which are notcaused by a failure of the power system phase voltage.The MiCOM P747 does this by looking at each zone. For each zone, if VTS detects a differential current anda voltage drop, it blocks the VT for that zone. This prevents the busbar differential element from signalling afault for that zone and tripping a circuit breaker.Ordinal Signal Name Source Type ResponseDescription1080 VT Chk Block Z1 Software VT Check Protection eventThis DDB signal indicates that the VT supervision blocks tripping of the busbar differential element for Zone 11081 VT Chk Block Z2 Software VT Check Protection eventThis DDB signal indicates that the VT supervision blocks tripping of the busbar differential element for Zone 21082 VT Chk Block Z3 Software VT Check Protection eventThis DDB signal indicates that the VT supervision blocks tripping of the busbar differential element for Zone 31083 VT Chk Block Z4 Software VT Check Protection eventThis DDB signal indicates that the VT supervision blocks tripping of the busbar differential element for Zone 4MiCOM P747 Chapter 6 - Monitoring and ControlP747-TM-EN-1 187
