NR Electric PCS-9611, Instruction Manual

Page: 83 / 300

3 Operation Theory
PCS-9611 Feeder Relay
3-47
Date: 2014-04-08
3.14 Zero Sequence Overvoltage Protection
3.14.1 Zero Sequence Overvoltage Protection Theory
On a healthy three-phase power system, the addition of each of the three-phase to earth voltages
is nominally zero. However, when an earth fault occurs on the primary system, the balance is
upset and a residual voltage is produced. Hence, a zero sequence overvoltage protection can be
used to offer earth fault protection on such a system.
The residual voltage could be measured at the secondary terminals of a voltage transformer
having a “broken delta” secondary connection, or it can be calculated from the three phase
voltages; which is decided by the setting [Opt_3U0].
This relay provides a two-stage zero sequence overvoltage protection with definite time delay
characteristics. The two stages have same protection logics.
The following figure shows the logic diagram of the stage 1 zero sequence overvoltage protection.
[59G1.En1]
[59G1.En]
U
0
> [59G1.3U0_Set]
&
[59G1.Op]
[59G1.St]
[59G1.Blk]
t
ROV1
0
Figure 3.14-1 Logic diagram of the stage 1 ROV protection
Where:
[59G1.3U0_Set] is the voltage setting of the stage 1 zero sequence overvoltage protection;
“t
ROV1
” is the setting [59G1.t_Op], the time setting of the stage 1 zero sequence overvoltage
protection;
[59G1.En] is logic setting of the stage 1 zero sequence overvoltage protectio n.
[59G1.En1] is the binary signal for enabling the stage 1 zero sequence overvoltage
protection;
[59G1.Blk] is the binary signal for blocking the stage 1 zero sequence overvoltage protection.
3.14.2 Zero Sequence Overvoltage Protection Settings
All the settings of the zero sequence overvoltage protection are listed in the following table. For
the information about the common explanation of the settings, see Section 7.3 .
No. Menu text Explanation Range Step
1 59G1.3U0_Set
The voltage setting of the stage 1 zero sequence
overvoltage protection
2~160V 0.001V
2 59G1.t_Op
The time s etting of the stage 1 zero sequence
overvoltage protection
0~100s 0.001s