Loss Of Excitation 40, 40-1, 40-2 - GE DGP Series Instruction Manual

2.3 PROTECTION FUNCTION SETTINGS
Algorithm: Impedance looking in to the machine is computed using delta voltage and delta current as shown in
the following equation. Functions 40-1 and 40-2 are identical, each with an adjustable time delay.
V V
–
a b
Z = ------------------ -
ab
I – I
2
a b
V V
–
a c
Z =
------------------ -
ac
I I
–
a c
Characteristic and setting criteria: See Figure 2–7: MHO CHARACTERISTICS FOR 40-1 & 40-2 FUNCTIONS.
With settings per the criteria shown in Figure 2–7: MHO CHARACTERISTICS FOR 40-1 & 40-2 FUNCTIONS,
function 40-1 detects the loss of excitation for about 30% or higher load conditions; function 40-2 detects for all
load conditions, However, some stable power system swing conditions may momentarily enter the 40-2 char-
acteristic. For security of the function under stable swing conditions, it is recommended to delay functions 40-1
and 40-2 by a minimum of 0.06 and 0.5 seconds, respectively.
Setting 501: SELV2SUP can be set to either 0 (DISABLE) or 1 (ENABLE). It is recommended to set this to
function to ENABLE unless an external VTFF is used via input DI6.
For the sample generator system,
( )
Z secondary
b
' (secondary) = 15.54 × 0.216 = 3.36 ohms
X
d
(secondary) = 15.54 × 1.967 = 30.57 ohms
X
d
Set 501: SELV2SUP to 1 (ENABLE).
Set the 40-1 setpoints to the following values:
15.54
CENTER =
-------------------------------- -
15.54
RADIUS =
-------------- -
2
TL12 = 0.06 seconds
Set the 40-2 setpoints to the following values:
30.57
CENTER
= -------------------------------- -
30.57
RADIUS =
-------------- -
2
TL12 0.5 seconds
=
2-
20
if Setting 109: PHASE = A-B-C
if Setting 109: PHASE = A-C-B
2
kV
CT Ratio
base ×
= ---------------------- - ---------------------- -
MVA VT Ratio
base
2
18 1600
×
= 15.54 ohms
= -------------------- - -------------- -
211.765 157.5
3.36
+
= 9.45 ohms
2
= 7.77 ohms
+ 3.36
16.97 ohms
=
2
= 15.28 ohms
DGP Digital Generator Protection System
2 CALCULATION OF SETTINGS

2.3.5 LOSS OF EXCITATION 40, 40-1, 40-2

GE Power Management