ABB RER615 - Page 359

Figure 175: Combined overadmittance and overconductance characteristic.
Left figure: classical origin-centered admittance circle combined with two
overconductance boundary lines. Right figure: admittance circle is set off from the
origin.
Combined overconductance and oversusceptance characteristic
The combined overconductance and oversusceptance criterion is enabled with the
Operation mode setting set to "Go, Bo".
By setting Directional mode to "Forward", the characteristic is a combination of two
boundary lines with the settings Conductance forward and Susceptance forward .
See Figure 176 .
By setting Directional mode to "Non-directional", the characteristic is a combination
of four boundary lines with the settings Conductance forward , Conductance
reverse , Susceptance forward and Susceptance reverse . See Figure 177 .
For the sake of application flexibility, the boundary lines can be tilted by the
angle defined with the Conductance tilt Ang and Susceptance tilt Ang settings. By
default, the tilt angles are zero degrees, that is, the boundary lines are straight
lines in the admittance plane. A positive Conductance tilt Ang value rotates
the overconductance boundary line counterclockwise from the vertical axis. A
positive Susceptance tilt Ang value rotates the oversusceptance boundary line
counterclockwise from the horizontal axis.
In case of the non-directional conductance and susceptance criteria, the
Conductance reverse setting must be set to a smaller value than Conductance
forward and the Susceptance reverse setting must be set to a smaller value than
Susceptance forward .
Operation is achieved when the measured admittance moves outside the
characteristic.
The combined overconductance and oversusceptance criterion is applicable in
high-resistance earthed, unearthed and compensated networks or in the systems
where the system earthing may temporarily change during normal operation from
compensated to unearthed system.
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
359