at low degrees of overexcitation, the very long delay is limited by 30 minutes, then theTRIP output signal of OEXPVPH (24) will be set to 1 and TMTOTRIP will reach 0seconds before THERMSTA reaches 100%.9.4.7.5 Overexcitation alarmA separate step, AlarmPickup, is provided for alarming purpose. It is normally set 2%lower than (Pickup1) and has a definite time delay, tAlarm. This will give the operatoran early abnormal voltages warning.9.4.7.6 Logic diagramANSI09000161-4-en.vsd³1ANDANDEi M=(Ei / f)(Vn / fn)M = relative Pickup as service valuePickup2M>Pickup2Pickup1M>Pickup1TDForIEEECalculationof internalinducedvoltage EiTD MMt>tAlarmt>tMinALARMTRIPAlarmPickupV3PBLOCK00-tAlarm00-tMin00-1800sANSI09000161 V4 ENFigure 128: A simplified logic diagram of the Overexcitation protection OEXPVPH(24)Simplification of the diagram is in the way the IEEE delays are calculated. The coolingprocess is not shown. It is not shown that voltage and frequency are separately checkedagainst their respective limit values.Section 9 1MRK 502 043-UUS BVoltage protection280Technical Manual
