ABB RELION RET670, Applications Manual

Page: 191 / 1016

• 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 (11) 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
67
shows a configuration for three phase tripping, but LDRGFC can be configured with
individual release to all phases trip. The BFI_3P signal can also, through one of the
available binary signal transfer channels, be sent to remote end and there connected to
input REMSTEP. Normally, the local criterion is sufficient.
1MRK 504 163-UUS A
Section 7
Differential protection
Transformer protection RET670 2.2 ANSI 185
Application manual