of the IED 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. 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.
4.4.2.5 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.
A070702 V2 EN (Equation 68)
Broken conductor fault situation can occur in phase A in a feeder.
IECA070699 V2 EN
Figure 242: Broken conductor fault situation in phase A in a distribution or
subtransmission feeder
Section 4 1YHT530004D05 D
Protection functions
454 615 series
Technical Manual
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