ABB RELION 620 Series Technical Manual page 616

Section 4
Protection functions
4.4.2.5
610
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.
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
is 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.
GUID-8B00BC40-DB72-4A9E-8CED-B3BD71C066A1 V1 EN
Figure 313: Broken conductor fault situation in phase A in a distribution or
subtransmission feeder
1MRS757644 F
(Equation 128)
I_A=0
I_B
I_C
620 series
Technical Manual
and I
2 1