ABB RELION RED670 Series Product Manual page 30

Line differential protection RED670 2.2
Product version: 2.2
IED
IED
IEC05000043 V2 EN-US
Figure 9. Five terminal lines with master-master system
RED
670
Comm.
Channels
RED
670
IEC05000044 V1 EN-US
Figure 10. Five terminal line with master-slave system
Current samples from IEDs located geographically apart from
each other, must be time coordinated so that the current
differential algorithm can be executed correctly, this is done
with the echo method. For applications where transmit and
receive times can differ, the optional built-in GPS receivers
can be used.
Additional security logic for differential protection LDRGFC
Additional security logic for differential protection (LDRGFC)
can help the security of the protection especially when the
communication system is in abnormal status or for example
when there is unspecified asymmetry in the communication
link. It helps to reduce the probability for mal-operation of the
protection. LDRGFC is more sensitive than the main
protection logic to always release operation for all faults
detected by the differential function. LDRGFC consists of four
sub functions:
• Phase-to-phase current variation
• Zero sequence current criterion
• Low voltage criterion
• Low current criterion
Phase-to-phase current variation takes the current samples
as input and it calculates the variation using the sampling
value based algorithm. Phase-to-phase current variation
function is major one to fulfill the objectives of the startup
element.
30
Protected zone
IED IED
Protected zone
RED RED
670 670
GUID-8F918A08-E50E-4E7B-BDCA-FF0B5534B289 v3
IED
Comm.
Channels
IEC0500043_2_en.vsd
RED
670
en05000044.vsd
The communication link is continuously monitored, and an
automatic switchover to a standby link is possible after a
preset time.
Zero sequence criterion takes the zero sequence current as
input. It increases the security of protection during the high
impedance fault conditions.
Low voltage criterion takes the phase voltages and phase-to-
phase voltages as inputs. It increases the security of
protection when the three-phase fault occurred on the weak
end side.
Low current criterion takes the phase currents as inputs and
it increases the dependability during the switch onto fault
case of unloaded line.
The differential function can be allowed to trip as no load is
fed through the line and protection is not working correctly.
Features:
1MRK 505 379-BEN C
ABB