Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.4.3.6
REX640
Technical Manual
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
GUID-C8E52A65-EEFA-4BDC-B71A-E1B1D8ABE93F V1 EN
Broken conductor fault situation can occur in phase A in a feeder.
GUID-C199862D-A111-47BA-B716-20AEB7AF8F9D V1 EN
Figure 413: Broken conductor fault situation in phase A in a distribution or
subtransmission feeder
Section 4
Protection functions
(Equation 190)
I_A=0
I_B
I_C
and I
2 1
751