GE G60 Instruction Manual page 222

5.5 GROUPED ELEMENTS
5
We have the magnitude of neutral voltage V
and the magnitude of the neutral and zero-sequence voltages
Therefore, under the normal conditions described above, we set the operating quantities as follows:
In actual practice, the Pickup ratio may vary from 0.4 to 0.85.
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:
and the magnitude of the neutral and zero-sequence voltages
5-140
E3
E3
E3
k
VN
3 (
Vn rd
3 ( ) +
Vn rd
and
3 (
Vo rd
Vn(3rd)
3 ( ) +
Vn rd
and
3 ( ) +
Vn rd Vo
Figure 5–90: 100% STATOR GROUND APPLICATION EXAMPLE
as:
N
×
R E
3
V ----------------- -
=
N
R jX
–
c
⇒
V 7.07 V
=
N
×
jX E
– j50
–
c 3
V ----------------------- - ------------- -
= =
0
R jX 5 j5
– –
c
⇒
V V 10 pu
+ =
N 0
V
N
>
Pickup ---------------------- -
V V
+
N
<
Supervision V
N
×
V k E
=
N 3
G60 Generator Management Relay
VA VB VC
)
<
Pickup
3 ( )
Vo rd
Va(3rd)
)
Vb(3rd)
< 1 −
Pickup S
>
3 ( )
Vo rd
3Vo
(3rd)
3 ( ) <
rd Supervisio n
>
×
10 5 10
--------------- - V --------- - V
= =
5 j5 1 j –
–
V V as:
+
N 0
j10
10 j10
–
–
---------- - ⇒
V V -------------------- -
= + =
N 0
1 j –
1 j –
0.707
0.707 pu
-------------- -
= =
10
0
V 10 pu
+ =
0
E 10 V , R 5Ω, X
= = =
3 c
×
0.15 10 1.5
= =
V V as:
+
N 0
5 SETTINGS
Vc(3rd)
5Ω, and k 0.15 .
=
GE Multilin
(EQ 5.35)
(EQ 5.36)
(EQ 5.37)
(EQ 5.38)