Negative Phase Sequence Directional Blocking
The direction of Negative Phase Sequence (NPS) overcurrent faults can be determined by their Fault Angle.
The Fault Angle is the relationship between the negative phase sequence current INPS and the negative phase sequence voltage VNPS. that is VNPS → INPS.
For example, VNPS = 60°, INPS = 180° Therefore NPS Fault Angle = 120°
VNPS is used as the polarising voltage and a Low Block setting is used to determine the action taken when VNPS is below the Low Threshold setting.
The tripping direction for NPS faults may be:
-
Trip Forward
-
Trip Reverse
-
Trip Forward and Reverse (that is non directional)
Operational values for directional NPS are shown below:
|
Polarizing Method |
Fault Angle |
Characteristic Fault Angle (default) |
Low Threshold (default) |
Range |
|---|---|---|---|---|
|
VNPS |
VNPS→INPS |
120° |
VNPS=500 V |
Adjustable VNPS300 to 2000 V |