Phase Characteristic Fault Angle
The Characteristic Angle defines the forward and reverse fault regions for the network.
When a phase fault is detected, its fault angle is calculated and compared to the Phase 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 is a reverse fault.
The Phase Characteristic Angle is configurable over the range -179° to 180°.
-45° is the default Characteristic Angle for Phase faults. So an A phase fault where the fault current lagged the polarising voltage by 45° would be a forward fault in the centre of the forward sector. The Angle at Fault reported in the Event Log would be -45° .
When Protection Groups A and B are active, the Event Log will also record:
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Forward Pickup Phase A
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Protection Group A Active
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Forward Phase Protection Trip
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Angle at Fault -45°
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Polarising Voltage at Trip VQUAD
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Polarising Voltage at the Maximum VQUAD
A reverse fault where the fault current led the polarising voltage by 135° would log the events below.
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Reverse Pickup Phase A
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Protection Group B Active
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Reverse Phase Protection Trip
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Angle at Fault 135°
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Polarising Voltage at Trip VQUAD
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Polarising Voltage at the Maximum VQUAD
Phase fault currents and their associated quadrature voltages are shown in the table below.