GE DGP Series, Instruction Manual

Page: 63 / 278

GE Power Management DGP Digital Generator Protection System 2-
23
2 CALCULATION OF SETTINGS 2.3 PROTECTION FUNCTION SETTINGS
2
Characteristics: The following four graphs show the curves for selected values of K and Voltage Restraint. The
curve for any combination of K and Restraint Voltage can be determined with the above algorithm.
This function should be set to coordinate with the power system protective relays used at the generating sta-
tion. Also, the PICKUP setting should be a safe margin above the expected maximum load on the machine.
Refer to Section 2.3.19: ACCIDENTAL ENERGIZATION AE on page 2–37 for additional considerations regard-
ing the 51V PICKUP setting.
For the sample generator system,
set PICKUP= 1.75
×
generator rated load current
= 1.75
×
4.25 A
= 7.5 A secondary
Setting 1004: TIME FAC ( K ) should be selected to back up the relays on transmission lines out of the generat-
ing station. As the information about line relays is not known, set TIME FAC such that the operate time of 51V
for a 3-phase fault on the high side of the GSU is about 0.75 second. For simplicity, power system contribution
to the fault is not considered in the following calculations.
Generator contribution = 4.25 / 0.322 = 13.2 A secondary
Multiple of PICKUP = 13.2 / 7.5 = 1.76
Generator terminal voltage =
% restraint =
TIME FAC (K) =
set TIME FAC = 1.0
Impedance to fault 21.6 10
211.765
200
---------------------
×
 
 
+ 21.6 10.6 + 32.2% at machine base = = =
18
10.6
32.2
-----------
×
5.93 = kV
5.93
18
----------- 100
×
32.9% =
0.75
1.76
0.329
--------------- 1 –
 
 
×
0.985 or higher =