ABB RELION REX640 Technical Manual page 506

Protection and control

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Protection functions

Figure 288: 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

conductance and Circle susceptance settings. Also the boundary lines can be tilted

by the angle defined with the

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

vertical axis.

In case of the non-directional conductance criterion, the

setting must be set to a smaller value than

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.

Conductance tilt Ang setting rotates boundary lines counterclockwise from the

Conductance tilt Ang setting. By default, the Circle

Conductance forward .

1MRS759142 F

Conductance reverse

Technical Manual