GE G60 UR Series, Instruction Manual

Page: 329 / 634

GE Multilin G60 Generator Protection System 5-197
5 SETTINGS 5.6 GROUPED ELEMENTS
5
Figure 5–111: 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) ( ) rd 3 (
) rd 3 (
0
<
+ V V
V
n
n
and
Pickup 1
3rd) ( ) rd 3 (
) rd 3 (
0
0 - >
+ V V
V
n
and
n Supervisio 3rd) ( ) rd 3 (
0
> + V V
n
Va Vb Vc
E3
E3
E3
Vn
k
3V
0 (3rd)
V
N
R E
3
×
R jX
c
–
------------------
10 5
×
5 j 5 –
----------------
V
10
1 j –
----------
V = = =
V
N
⇒
7.07 V
=
V
N
V
0
+
V
0
jX
c
– E
3
×
R jX
c
–
------------------------
j 50
–
5 j 5 –
--------------
j 10
–
1 j –
-----------
= = = V
N
V
0
+
⇒
10 j 10
–
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
Ω
, X
c
5
Ω
, and k 0.15 = = =
V
N
k E
3
×
0.15 10
×
1.5
= = =
V
N
V
0
+