NPS Characteristic Fault Angle
The NPS Characteristic Fault Angle is the expected fault angle for a forward NPS overcurrent fault.
The Default Characteristic Angle for NPS EF Directional Protection is 120°. So an NPS fault where the NPS current INPS leads the NPS voltage VNPS by 120° would be a forward fault in the centre of the forward sector.
For NPS protection, the Characteristic Angle can be configured for a value between -179° and 180°.
When an NPS fault is detected, its fault angle is calculated and compared to the NPS Characteristic Angle to determine if the fault is forward or reverse. If the fault angle is within ± 90° * of the Characteristic Angle the fault is forward, otherwise it’s a reverse fault.
When Protection Groups A and B are active, an NPS fault at the Characteristic Angle would log the following events:
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Forward Pickup NPS
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Protection Group A Active
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Forward NPS Protection Trip
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Angle at Fault 120°
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Polarising Voltage at Trip VNPS
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Polarising Voltage at the Maximum VNPS
A reverse NPS fault where the fault current lags the polarising voltage by 60° would log the events below.
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Reverse Pickup NPS
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Protection Group B Active
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Reverse NPS Protection Trip
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Angle at Fault -60°
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Polarising Voltage at Trip VNPS
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Polarising Voltage at the Maximum VNPS