RED
670
Protected zone
Comm.
Channels
RED
670
RED
670
en05000044.vsd
RED
670
RED
670
IEC05000044 V1 EN
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
The communication link is continuously monitored, and an
automatic switchover to a standby link is possible after a preset
time.
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.
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:
• Startup element is sensitive enough to detect the
abnormal status of the protected system
• Startup element does not influence the operation speed of
main protection
• Startup element would detect the evolving faults, high
impedance faults and three phase fault on weak side
• It is possible to block the each sub function of startup
element
• Startup signal has a settable pulse time
4. Impedance protection
Distance measuring zone, quadrilateral characteristic
ZMQPDIS, ZMQAPDIS
The line distance protection is an up to five (depending on
product variant) zone full scheme protection function with three
fault loops for phase-to-phase faults and three fault loops for
phase-to-earth faults for each of the independent zones.
Individual settings for each zone in resistive and reactive reach
gives flexibility for use as back-up protection for transformer
connected to overhead lines and cables of different types and
lengths.
ZMQPDIS together with Phase selection with load
encroachment FDPSPDIS has functionality for load
encroachment, which increases the possibility to detect high
resistive faults on heavily loaded lines, as shown in figure11.
1MRK 505 346-BEN -
Line differential protection RED670 2.1 IEC
Product version: 2.1
24 ABB
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