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4.5. Function 67NI. Directional neutral isolated overcurrent
Depending on model, two neutral directional units are available: 67NI_1 and 67NI_2.
This function is based on two supervisions: The analogue to the one that uses the 67N to check
that the residual current is inside the defined area by the settings of directionality, operation
angle and halfcone, and the second supervision of the modules of the residual voltage and
current.
To perform the directional detection, the residual voltage is used as polarization magnitude and
the residual current as an operating magnitude. The intervention sector in forward direction is
defined in the following way: the operating angle is rotated anticlockwise from the negative
residual voltage,-V0 which gives us the maximum torque direction. A cone is drawn, with the
half-cone angle adjusted, over this maximum torque direction. In the same way, the intervention
sector in reverse direction is defined in the following way: the operating angle is rotated
anticlockwise from the positive residual voltage,V0 which gives us the maximum torque direction.
A cone is drawn, with the half-cone angle adjusted, over this maximum torque direction.
Forward Inverse
To perform the module evaluation , it is used the residual voltage and the residual current
measurements, defining a working area according the settings of low and high currents and the
low and high voltages.
Working area characteristic of I0 and V0