GE Multilin G30 Generator Protection System 5-2055 SETTINGS 5.6 GROUPED ELEMENTS5The operating characteristic is shaped out of two offset mho circles shifted down along the imaginary axis as shown below.Figure 5–91: LOSS OF EXCITATION OPERATING CHARACTERISTICSSTAGE 1 SETTINGS:The stage 1 characteristic is typically set to detect a loss of excitation for load conditions of 30% of the nominal or higher.This is achieved with a mho element with a diameter equal to the base impedance of the machine and an offset equal tohalf the machine transient reactance (X′d).(EQ 5.52)The stage 1 element should be time delayed to allow for blocking by the VT fuse failure element (50 ms).STAGE 2 SETTINGS:The stage 2 characteristic is typically set to detect a loss of excitation for all load conditions. This is achieved with a mhoelement with a diameter equal to the synchronous reactance of the machine and an offset equal to half the machine tran-sient reactance (X′d).(EQ 5.53)During stable power swing conditions the positive-sequence impedance may momentarily enter the stage 2 characteristic.For security of the function under such conditions, it is recommended to delay stage 2 by a minimum of 0.5 seconds.MESSAGE LOSS OF EXCITATIONRADIUS 2: 10.00 ohmRange: 0.10 to 300.00 ohms in steps of 0.01MESSAGE LOSS OF EXCITATIONV SUPV 2: EnabledRange: Disabled, EnabledMESSAGE LOSS OF EXCITATIONPKP DELAY2: 0.500 sRange: 0.000 to 65.535 s in steps of 0.01MESSAGE LOSS OF EXCITATIONUV SUPV: 0.700 puRange: 0.000 to 1.250 pu in steps of 0.001MESSAGE LOSS OF EXCIT BLK:OffRange: FlexLogic operandMESSAGE LOSS OF EXCITATIONTARGET: Self-resetRange: Self-reset, Latched, DisabledMESSAGE LOSS OF EXCITATIONEVENTS: DisabledRange: Disabled, Enabled830711A1.CDRC1ZbXdRC1R1C2R2ZbX’dXd= Center of element 1 = (Zb + X’d) / 2= Radius of element 1 = Zb / 2= Center of element 2 = (Xd + X’d) / 2= Radius of element 2 = Xd / 2= Base impedance of the machine= Transient reactance of the machine= Synchronous reactance of the machineXX’d2R1R2C2CENTER 1 Zb X′d+2-----------------------, RADIUS 1 Zb2-------= =CENTER 2 Xd X′d+2-----------------------, RADIUS 1 Xd2-------= =
