ABB Relion 670 series, Technical Reference Manual

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Zero sequence criterions 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
5.3.2 Principle of operation
Additional security logic for differential protection (STSGGIO, 11) takes the current
samples, current RMS values, phase voltage values, phase-to-phase voltage values,
zero sequence current and remote side startup signals as inputs.
Startup signal becomes activated when any one of the current variation startup signal,
zero sequence current startup signal, voltage startup signal, and current startup signal is
activated.
Phase-to-phase current variation takes current samples and generates the startup signal
by comparing with the pickup value.
If the zero sequence current value is greater than the pickup value of zero sequence
current then the zero sequence current startup signal will be activated.
Voltage startup signal becomes activated when the any of phase voltage and line
voltage is less than the voltage pickup value and the remote startup signal has to be
activated.
Current startup signal becomes activated when the current value in all phases is less
than current pickup value.
1MRK505222-UUS C
Section 5
Differential protection
165
Technical reference manual