Application - ABB 615 series Technical Manual

Section 4
Protection functions
4.4.2.5
596

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.
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-sequence and negative-sequence
currents. This gives 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
the positive-sequence current value. The unbalance is calculated with the equation.
I
2
Iratio
=
I
1
A070702 V2 EN
Broken conductor fault situation can occur in phase A in a feeder.
IECA070699-ANSI V1 EN
Figure 301: Broken conductor fault in phase A in a distribution or subtransmission
feeder
1MAC059074-MB A
and I is
2 1
(Equation 116)
615 series ANSI
Technical Manual