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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 operation 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.
4.3.2.5
Application
In three-phase distribution and subtransmission network applications the phase
discontinuity in one phase can cause an increase of zero-sequence voltage and
short overvoltage peaks and also oscillation in the corresponding phase.
PDNSPTOC is a three-phase protection with DT characteristic, designed for
detecting broken conductors in distribution and subtransmission networks. The
function is applicable for both overhead lines and underground cables.
The operation of PDNSPTOC is based on the ratio of the positive-sequence
and negative-sequence currents. This gives a better sensitivity and stability
compared to plain negative-sequence current protection since the calculated ratio
of positive-sequence and negative-sequence currents is relatively constant during
load variations.
The unbalance of the network is detected by monitoring the negative-sequence and
positive-sequence current ratio, where the negative-sequence current value is I
2
and I
1
is the positive-sequence current value. The unbalance is calculated with the
equation.
Iratio
I
I
=
2
1
(Equation 43)
Broken conductor fault situation can occur in phase A in a feeder.
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
417
Содержание Relion REC615
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