GE Multilin g60, Instruction Manual

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5-234 G60 Generator Protection System GE Multilin
5.6 GROUPED ELEMENTS 5 SETTINGS
5
The operating characteristic is shaped out of two offset mho circles shifted down along the imaginary axis as shown below.
Figure 5–122: 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
′
d ).
(EQ 5.32)
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 ).
(EQ 5.33)
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
setting specifies a FlexLogic operand for blocking the feature based on user-programmable condi-
tions. When the blocking input is asserted, the element resets its timers, de-asserts the
PKP
and
OP
operands (if asserted),
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.
MESSAGE
LOSS OF EXCITATION
TARGET: Self-reset
Range: Self-reset, Latched, Disabled
MESSAGE
LOSS OF EXCITATION
EVENTS: Disabled
Range: Disabled, Enabled
830711A1.CDR
C1
Zb
Xd
R
C1
R1
C2
R2
Zb
X’d
Xd
= 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 machine
X
X’d 2
R1
R2
C2
CENTER 1
Zb X
′
d
+
2
-----------------------
, RADIUS 1
Zb
2
-------
= =
CENTER 2
Xd X
′
d
+
2
-----------------------
, RADIUS 1
Xd
2
-------
= =