GE Multilin g60

GE Multilin G60 Generator Protection System 5-205
5 SETTINGS 5.6 GROUPED ELEMENTS
5
Figure 5–112: 100% STATOR GROUND APPLICATION EXAMPLE
We have the magnitude of neutral voltage V
N
as:
(EQ 5.36)
and the magnitude of the neutral and zero-sequence voltages as:
(EQ 5.37)
Therefore, under the normal conditions described above, we set the operating quantities as follows:
(EQ 5.38)
In actual practice, the |V
N
|/|V
N
+ V
0
| ratio may vary from 0.4 to 0.85 under normal conditions. The pickup and supervision
setpoints are determined by evaluating the operating quantities during a fault condition (refer to example 2 for details).
Example 2: Operating quantities for a fault at a fraction k from the neutral grounding point.
For analysis, consider the above figure and assume that .
In this case, we have the magnitude of the neutral voltage at:
(EQ 5.39)
and the magnitude of the neutral and zero-sequence voltages as:
830737A1.CDR
S
Vn (3rd)
Va (3rd)
Vb (3rd)
Vc (3rd)
Pickup
3rd)()rd3(
)rd3(
0
<
+ VV
V
n
n
and
Pickup1
3rd)()rd3(
)rd3(
0
0
->
+ VV
V
n
and
nSupervisio3rd)()rd3(
0
>+ VV
n
Va
Vb
Vc
E3
E3
E3
Vn
k
3V
0 (3rd)
V
N
RE
3

RjX
c
–
------------------
10 5
5 j5–
----------------
V
10
1 j–
----------
V== =
V
N
 7.07 V=
V
N
V
0
+
V
0
jX
c
– E
3

RjX
c
–
------------------------
j50–
5 j5–
--------------
j10–
1 j–
-----------
===V
N
V
0
+
10 j10–
1 j–
-------------------- -=
V
N
V
0
+ 10 pu=
Pickup
V
N
V
N
V
0
+
-----------------------

7.07
10
----------- 0.707 pu==
Supervision V
N
V
0
+ 10 pu=
E
3
10 V= , R 5, X
c
5, and k 0.15== =
V
N
kE
3
 0.15 10 1.5== =
V
N
V
0
+