Loss Of Excitation - GE 489 Instruction Manual

4.7 S6 VOLTAGE ELEMENTS
T

LOSS OF EXCITATION

T
[ENTER] for more
4
Loss of excitation is detected with an impedance element. When the impedance falls within the impedance circle for the
specified delay time, a trip will occur if it is enabled. Circles 1 and/or 2 can be tuned to a particular system. The larger circle
diameter should be set to the synchronous reactance of the generator, x
reactance x' / 2. Typically the smaller circle (if used) is set to minimum time with a diameter set to 0.7 x
d
x' / 2. This feature is blocked if voltage supervision is enabled and the generator voltage is above the
d
point. The trip feature is supervised by minimum current of 0.05 × CT. Note that the Loss of Excitation element will be
blocked if there is a VT fuse failure or if the generator is offline. Also, it uses output CT inputs.
The secondary phase-phase loss of excitation impedance is defined as:
V
AB
Z M
= --------------- =
loe
I I
–
A B
where: Z = secondary phase-to-phase loss of excitation impedance
loe
∠θ
M = Secondary impedance phasor (magnitude and angle)
loe loe
All relay quantities are in terms of secondary impedances. The formula to convert primary impedance quantities to second-
ary impedance quantities is provided below.
Z
primary
Z
= --------------------------------------------------
sec ondary
where: Z = primary ohms impedance
primary
CT Ratio = programmed CT ratio, if CT ratio is 1200:5 use a value of 1200 / 5 = 240
VT Ratio = programmed VT ratio, if VT ratio is 100:1 use a value of 100
4-38
ð
ENABLE VOLTAGE
ENTER
SUPERVISION: Yes
ESCAPE
VOLTAGE
ESCAPE
LEVEL: 0.70 x Rated
MESSAGE
CIRCLE 1
ESCAPE
TRIP: Off
MESSAGE
ASSIGN CIRCLE 1 TRIP
ESCAPE
RELAYS (1-4): 1---
MESSAGE
CIRCLE 1
ESCAPE
DIAMETER: 25.0 Ωsec
MESSAGE
CIRCLE 1
ESCAPE
OFFSET: 2.5 Ωsec
MESSAGE
CIRCLE 1 TRIP
ESCAPE
DELAY: 5.0 s
MESSAGE
CIRCLE 2
ESCAPE
TRIP: Off
MESSAGE
ASSIGN CIRCLE 2 TRIP
ESCAPE
RELAYS (1-4): 1---
MESSAGE
CIRCLE 2
ESCAPE
DIAMETER: 35.0 Ωsec
MESSAGE
CIRCLE 2
ESCAPE
OFFSET: 2.5 Ωsec
MESSAGE
CIRCLE 2 TRIP
ESCAPE
DELAY: 5.0 s
MESSAGE
∠ θ
loe loe
×
CT Ratio
VT Ratio
489 Generator Management Relay
4 SETPOINT PROGRAMMING
4.7.9 LOSS OF EXCITATION
Range: Yes, No
Range: 0.70 to 1.00 × Rated in steps of 0.01. Seen only if
ENABLE VOLTAGE SUPERVISION is Yes
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to 4
Range: 2.5 to 300.0 Ωsec in steps of 0.1
Range: 1.0 to 300.0 Ωsec in steps of 0.1
Range: 0.1 to 10.0 s in steps of 0.1
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to 4
Range: 2.5 to 300.0 Ωsec in steps of 0.1
Range: 1.0 to 300.0 Ωsec in steps of 0.1
Range: 0.1 to 10.0 s in steps of 0.1
, and the circle offset to the generator transient
d
GE Power Management
and an offset of
d
set-
VOLTAGE LEVEL