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2 CALCULATION OF SETTINGS
This function is intended to alarm prior to a 24T trip, allowing an operator to take corrective action. Setting
1302: PICKUP should be below the continuous Volts/Hz rating of the generator or step-up transformer, which-
ever is lower. Timer TL6 (Setting 1303: TL6) should be set to minimize the nuisance alarms.
For the sample generator system, assume an allowable over V/Hz of 10%.
set PICKUP = 1 + (90% of 10%) per unit = 1.09 per unit
set TL6 = 2 seconds.
Algorithm:
K
T 1
=
-------------------------------------------------------------- - seconds
V F ⁄
-------------------------------------------- -
×
(
⁄
PU
V
F
NOM
K
T 2
=
------------------------------------------------- - seconds
V F ⁄
---------------------------------------- 1
×
⁄
PU
V
F
NOM
S
K
T 3
=
------------------------------------------------------------------ - seconds
V F ⁄
-------------------------------------------- -
×
(
⁄
V
F
PU
NOM
T 4
K seconds
=
where
T1 = Operating time for CURVE #1 (see Figure 2–12: TIME CHARACTERISTICS OF FUNCTION 24T
(CURVE 1) on page 2–31)
T2 = Operating time for CURVE #2 (see Figure 2–13: TIME CHARACTERISTICS OF FUNCTION 24T
(CURVE 2) on page 2–32)
T3 = Operating time for CURVE #3 (see Figure 2–14: TIME CHARACTERISTICS OF FUNCTION 24T
(CURVE 3) on page 2–33)
T4 = Operating time for CURVE #4 - characteristic of curve #4 is definite time providing the operating time
equal to K seconds if
V
>
×
PU
--- -
F
K = Time factor (Setting 1406: TIME FAC)
V
= nominal voltage (Setting 114: NOM VOLT)
NOM
F
= system frequency (Setting 102: SYSFREQ)
S
PU = V/Hz pickup (Setting 1405: INV PU)
1. The algorithm is processed separately for each phase.
2. V and V
values used are phase-ground voltages for wye-connected VTs. However, phase-phase volt-
NOM
ages are used for delta-connected VTs. The following table shows the voltages used by each of the three
GE Power Management
2.3.11 OVEREXCITATION ALARM (VOLTS/HERTZ: 24A)
2
–
1
)
S
–
0.5
–
1
)
S
V
NOM
-------------- -
F
S
DGP Digital Generator Protection System
2.3 PROTECTION FUNCTION SETTINGS
2.3.12 OVEREXCITATION TRIP (VOLTS/HERTZ: 24T)
2
2-
29
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