1MAC309294-MB F Section 4
Protection functions
RER620 181
Technical Manual
input, a horizontal communication input or an internal signal of the relay 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
trip timer is frozen to the prevailing value. In the “Block all” mode, the whole function is
blocked and the timers are reset. the “Block TRIP output” mode, the function operates
normally but the TRIP output is not activated.
4.1.7.5 Application
In three-phase distribution and subtransmission network applications the phase
discontinuity in one phase can cause increase of zero sequence voltage and short
overvoltage peaks and also oscillation in the corresponding phase.
46PD 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 46PD is based on the ratio of positive and negative sequence currents.
This gives better sensitivity and stability compared to plain negative sequence current
protection since the calculated ratio of positive and negative sequence currents is relatively
constant during load variations.
When the three phase currents are measured, the positive sequence current is calculated:
(Equation 28)
The negative sequence current is calculated:
(Equation 29)
phase current vectors
phase rotation operator (defined to rotate a phasor component forward by 120 degrees)
The unbalance of the network is detected by monitoring the negative 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:
(Equation 30)
Broken conductor fault situation can occur in phase A in a feeder.
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