GE G30 Instruction Manual page 345

5 SETTINGS
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The 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 CHARACTERISTICS
STAGE 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 to
half the machine transient reactance (X
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 mho
element with a diameter equal to the synchronous reactance of the machine and an offset equal to half the machine tran-
'
sient reactance (X d).
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.
GE Multilin
LOSS OF EXCITATION
RADIUS 2: 10.00 ohm
LOSS OF EXCITATION
V SUPV 2: Enabled
LOSS OF EXCITATION
PKP DELAY2: 0.500 s
LOSS OF EXCITATION
UV SUPV: 0.700 pu
LOSS OF EXCIT BLK:
Off
LOSS OF EXCITATION
TARGET: Self-reset
LOSS OF EXCITATION
EVENTS: Disabled
X
'
d).
Zb X'd
+
CENTER 1 ---------------------- - , RADIUS 1
=
2
Xd X'd
+
---------------------- - ,
CENTER 2 RADIUS 1
=
2
G30 Generator Protection System
5.6 GROUPED ELEMENTS
Range: 0.10 to 300.00 ohms in steps of 0.01
Range: Disabled, Enabled
Range: 0.000 to 65.535 s in steps of 0.01
Range: 0.000 to 1.250 pu in steps of 0.001
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
R
C1 = Center of element 1 = (Zb + X'd) / 2
R1 = Radius of element 1 = Zb / 2
C2 = Center of element 2 = (Xd + X'd) / 2
R2 = Radius of element 2 = Xd / 2
Zb = Base impedance of the machine
X'd = Transient reactance of the machine
Xd = Synchronous reactance of the machine
830711A1.CDR
Zb
------ -
=
2
Xd
------ -
=
2
5
(EQ 5.52)
(EQ 5.53)
5-205