GE G60 Instruction Manual page 394

5.6 GROUPED ELEMENTS
The operating characteristic is shaped out of two offset mho circles shifted down along the imaginary axis as shown below.
STAGE 1 SETTINGS:
5
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.
The
LOSS OF EXCIT BLK
tions. When the blocking input is asserted, the element resets its timers, de-asserts the
clears self-reset targets, logs a 'blocked' event if events are enabled, and becomes inactive. When unblocked, the element
will start functioning instantly. If exposed to pickup conditions for an extended period of time and unblocked, the element
will pickup and start timing out at the moment of unblocking.
5-234
LOSS OF EXCITATION
MESSAGE
TARGET: Self-reset
LOSS OF EXCITATION
MESSAGE
EVENTS: Disabled
X
Figure 5–122: LOSS OF EXCITATION OPERATING CHARACTERISTICS
'
d).
Zb
---------------------- - ,
CENTER 1
=
Xd
CENTER 2 ---------------------- - ,
=
setting specifies a FlexLogic operand for blocking the feature based on user-programmable condi-
G60 Generator Protection System
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
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
X'd Zb
+
------ -
RADIUS 1
=
2 2
X'd Xd
+
RADIUS 1 ------ -
=
2 2
5 SETTINGS
R
830711A1.CDR
(EQ 5.32)
(EQ 5.33)
and operands (if asserted),
PKP OP
GE Multilin