Application - ABB RELION 670 Series Applications Manual

Section 6
Differential protection
6.4.2

Application

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 reduces 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 (IL1–IL2, IL2–IL3, etc.) as input and
it calculates the variation using the sampling value based algorithm. Phase-to-phase current
variation function is major one to fulfil the objectives of the start up element.
Zero sequence criterion takes the zero sequence current as input. It increases 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 detects 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
The Additional security logic for differential protection LDRGFC is connected as a local
criterion to release the tripping from line differential protection. LDRGFC is connected with an
AND gate to the trip signals from LDLPDIF function. Figure
phase tripping, but LDRGFC can be configured with individual release to all phases trip. The
START signal can also, through one of the available binary signal transfer channels, be sent to
remote end and there connected to input REMSTUP. Normally, the local criterion is sufficient.
142
1MRK 504 152-UEN B
GUID-93AF4444-C7ED-4DF5-9379-176DF17AE22C v4
54 shows a configuration for three
Application manual