ABB RELION REX640, Техническое руководство, Страница: 835 / 1960

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.
4.4.3.6 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 236)
Broken conductor fault situation can occur in phase A in a feeder.
I_C
I_A=0
I_B
Figure 472: Broken conductor fault situation in phase A in a distribution or
subtransmission feeder
1MRS759142 F Protection functions
REX640
Technical Manual
835