CHAPTER 6: SETPOINTS S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 6–67
The diagram below shows the regions for detection of neutral current Forward and
Reverse directions with respect to the zero sequence voltage and the selected Maximum
Torque Angle (MTA).
When “Dual” polarizing is selected, the Reverse direction is declared if both directional
comparators - the one based on the zero sequence polarizing voltage, and the other based
on measured ground polarizing current - declare Reverse direction. If the direction from
one of the comparators declares Forward direction and the other declares Reverse
direction, the neutral directional element is undefined (see following table). If the polarizing
voltage falls below the set minimum voltage, the direction declared depends on the
polarizing ground current, assuming the measured ground current is above some 5% CTg.
The same rule applies if the ground current falls below 5% CTg. In this case the direction is
determined using the polarizing zero sequence voltage, assuming it is above the set
minimum voltage from the settings menu.
When direction is undefined, the “BLK NOC DIR UNDEF” setting determines whether neutral
overcurrent protection must be blocked (setting = Enabled) or enabled (setting= Disabled).
Table 6-10: Neutral directional element directions
Directional type Current direction Voltage direction Result
Current Undefined - Undefined
FW FW
RV RV
Voltage - Undefined Undefined
FW FW
RV RV
To Next Page
Loading...
