GE 489 - Manual (Page 92)

4-42 489 Generator Management Relay GE Multilin
4.7 S6 VOLTAGE ELEMENTS 4 SETPOINTS
4
4.7.9 LOSS OF EXCITATION
PATH: SETPOINTS ÖØ S6 VOLTAGE ELEMENTS ÖØ LOSS OF EXCITATION
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
d
, and the circle offset to the generator transient
reactance x’
d
/ 2. Typically the smaller circle (if used) is set to minimum time with a diameter set to 0.7x
d
and an offset of
x’
d
/ 2. This feature is blocked if voltage supervision is enabled and the generator voltage is above the VOLTAGE LEVEL set-
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:
(EQ 4.23)
where: Z
loe
= secondary phase-to-phase loss of excitation impedance
M
loe
∠θ
loe
= Secondary impedance phasor (magnitude and angle)
All relay quantities are in terms of secondary impedances. The formula to convert primary impedance quantities to second-
ary impedance quantities is provided below.
(EQ 4.24)
„ LOSS OF EXCITATION
„ [ENTER] for more
ENABLE VOLTAGE
SUPERVISION: Yes
Range: Yes, No
VOLTAGE
LEVEL: 0.70 x Rated
Range: 0.70 to 1.00 × Rated in steps of 0.01. Seen only if
ENABLE VOLTAGE SUPERVISION is "Yes"
CIRCLE 1
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN CIRCLE 1 TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to 4
CIRCLE 1
DIAMETER: 25.0
Ωsec
Range: 2.5 to 300.0 Ωsec in steps of 0.1
CIRCLE 1
OFFSET: 2.5
Ωsec
Range: 1.0 to 300.0 Ωsec in steps of 0.1
CIRCLE 1 TRIP
DELAY: 5.0 s
Range: 0.1 to 10.0 s in steps of 0.1
CIRCLE 2
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN CIRCLE 2 TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to 4
CIRCLE 2
DIAMETER: 35.0
Ωsec
Range: 2.5 to 300.0 Ωsec in steps of 0.1
CIRCLE 2
OFFSET: 2.5
Ωsec
Range: 1.0 to 300.0 Ωsec in steps of 0.1
CIRCLE 2 TRIP
DELAY: 5.0 s
Range: 0.1 to 10.0 s in steps of 0.1
ENTER
ESCAPE
р
р
MESSAGE
ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
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ESCAPE
Z
loe
V
AB
I
A
I
B
–
--------------- M
loe
θ
loe
∠
= =
Z
ondary sec
Z
primary
CT Ratio ×
VT Ratio
-------------------------------------------------- =