Figure 222: Forward directional oversusceptance characteristic. Left figure: classical
forward directional oversusceptance criterion. Middle figure: characteristic is tilted
with negative tilt angle. Right figure: characteristic is tilted with positive tilt angle.
Combined overadmittance and overconductance characteristic
The combined overadmittance and overconductance criterion is enabled with the
Operation mode setting set to "Yo, Go" and Directional mode to "Non-directional".
The characteristic is a combination of a circle with the radius defined with the
Circle radius setting and two overconductance boundary lines with the settings
Conductance forward and Conductance reverse. For the sake of application
flexibility, the midpoint of the circle can be moved from the origin with the
Circle
conductance and Circle susceptance settings. Also the boundary lines can be tilted
by the angle defined with the
Conductance tilt Ang setting. By default, the Circle
conductance and Circle susceptance are 0.0 mS and Conductance tilt Ang equals
zero degrees, that is, the characteristic is a combination of an origin-centered
circle with two vertical overconductance boundary lines. A positive tilt value for
the
Conductance tilt Ang setting rotates boundary lines counterclockwise from the
vertical axis.
In case of the non-directional conductance criterion, the
Conductance reverse
setting must be set to a smaller value than
Conductance forward.
Operation is achieved when the measured admittance moves outside the
characteristic.
The combined overadmittance and overconductance criterion is applicable in
unearthed, high-resistance earthed and compensated networks or in systems
where the system earthing may temporarily change during normal operation from
compensated network to unearthed system.
Compared to the overadmittance criterion, the combined characteristic improves
sensitivity in high-resistance earthed and compensated networks. Compared to the
non-directional overconductance criterion, the combined characteristic enables the
protection to be applied also in unearthed systems.
1MRS757644 H
Protection functions
620 series
Technical Manual
445
