4–148 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION CHAPTER 4: SETPOINTS
Figure 4-52: Third Harmonic Voltage Difference Application Example
We have the magnitude of neutral voltage V
N
as:
and the magnitude of the neutral and zero-sequence voltages |V
N
+ V
0
| as:
Therefore, under the normal conditions described above, we set the operating quantities
as follows:
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).
Vn (3rd)
Va
Vb
Vc
Va Vb Vc
E3
E3
E3
Vn
k
3V
0
(3rd)
Pickup
3rd)(
)
rd3(
)rd3(
0
VV
V
n
n
and
Pickup1
3rd)()rd3(
)rd3(
0
0
VV
V
n
and
n
Supervisio3rd)()rd3(
0
VV
n
3
rd
3V
0
894141.cdr
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