Neutral Admittance Characteristics - ABB RELION REX640 Technical Manual

1MRS759142 C
4.2.4.6
REX640
Technical Manual
deactivated. The timer calculates the start duration value START_DUR, which
indicates the percentage ratio of the start situation and the set operation time. The
value is available in the monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in Configuration/System/
Blocking mode which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK signal activation is
preselected with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode,
the operate timer is frozen to the prevailing value, but the OPERATE output is not
deactivated when blocking is activated. In the "Block all" mode, the whole function is
blocked and the timers are reset. In the "Block OPERATE output" mode, the function
operates normally but the OPERATE output is not activated.

Neutral admittance characteristics

The applied characteristic should always be set to cover the total admittance of the
protected feeder with a suitable margin. However, more detailed setting value
selection principles depend on the characteristic in question.
The settings defining the admittance characteristics are given in
primary milliSiemens.
The forward and reverse boundary settings should be set so that the forward setting is
always larger than the reverse setting and that there is space between them.
Overadmittance characteristic
The overadmittance criterion is enabled with the setting Operation mode set to "Yo".
The characteristic is a circle with the radius defined with the Circle radius setting. For
the sake of application flexibility, the midpoint of the circle can be moved away from
the origin with the Circle conductance and Circle susceptance settings. Default values
for Circle conductance and Circle susceptance are 0.0 mS, that is, the characteristic
is an origin-centered circle.
Operation is achieved when the measured admittance moves outside the circle.
The overadmittance criterion is typically applied in unearthed networks, but it can also
be used in compensated networks, especially if the circle is set off from the origin.
Section 4
Protection functions
467