Protection Functions
90 PRS-7367
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.
3.13.1.1 Function Block
The function block of the protection is as below.
U3P
59G
Blk
Blk_Op
Blk_Str
Op
Str
Alm
Figure 3.13-1 Function block
3.13.1.2 Signals
Table 3.13-1 Input Signals
The voltage in all the three phases
This signal blocks all the binary output signals of the function
This signal blocks all the start outputs of the function
This signal blocks all the trip signals of the function.
Table 3.13-2 Output Signals
This is the integrated start signal
This is the integrated operation signal.
This is the integrated Alarm signal
3.13.2 59G Protection Principle
The residual overvoltage protection function can be enabled or disabled by setting the
corresponding 59G_Ena parameter values as "1" or "0".
The residual voltage sample method is determined by 59G_U0_Calc, if 59G_U0_Calc =0, the
voltage is sample from external terminal, if 59G_U0_Calc = 1, the voltage is calculated by three
phases voltage.
The operation of residual overvoltage protection can be described by using a module diagram. All
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