ABB RET670 Applications Manual page 588

Section 3
IED application
582
bigger phase angle difference can be allowed as this is sometimes the case in a long
and loaded parallel power line. For this application we accept a synchronism check
with a long operation time and high sensitivity regarding the frequency difference. The
phase angle difference setting can be set for steady state conditions.
Another example, is when the operation of the power net is disturbed and high-speed
auto-reclosing after fault clearance takes place. This can cause a power swing in the net
and the phase angle difference may begin to oscillate. Generally, the frequency
difference is the time derivative of the phase angle difference and will, typically
oscillate between positive and negative values. When the circuit breaker needs to be
closed by auto-reclosing after fault-clearance some frequency difference should be
tolerated, to a greater extent than in the steady condition mentioned in the case above.
But if a big phase angle difference is allowed at the same time, there is some risk that
auto-reclosing will take place when the phase angle difference is big and increasing. In
this case it should be safer to close when the phase angle difference is smaller.
To fulfill the above requirements the synchronism check function is provided with
duplicate settings, one for steady (Manual) conditions and one for operation under
disturbed conditions (Auto).
SynchroCheck
VHighBusSC > 50 – 120% of VBaseBus
VHighLineSC >50 – 120% of VBaseLine
VDiffSC < 0.02 – 0.50 p.u.
PhaseDiffM < 5 – 90 degrees
PhaseDiffA < 5 – 90 degrees
FreqDiffM < 3 – 1000 mHz
FreqDiffA < 1000 mHz
ANSI10000079 V1 EN
Figure 223: Principle for the synchronism check function
Energizing check
The main purpose of the energizing check function is to facilitate the controlled re-
connection of disconnected lines and buses to energized lines and buses.
Bus voltage
Fuse fail
Line Bus Voltage
Fuse fail Line Voltage
1MRK504116-UUS C
52
Line
reference
voltage
ANSI10000079-1-en.vsd
Application manual