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S4 CONTROLS
6–146
In order to perform the synchrocheck function, the device uses only one voltage from each
end of the breaker. Voltage values to be compared must be on the same basis, either
phase-to-phase or phase-to-ground voltage. Also, they must be the same at both ends of
the breaker. It is not possible to compare a phase-to-ground voltage at one end with a
phase-to-phase voltage at the other end.
Additionally, if on one end, three voltages have been connected, the necessary voltage on
the other end for synchrocheck will only be single-phase voltage. If there is only one
voltage (either phase-to-phase or phase-to-ground) at both ends of the breaker, this must
be the same phase in both cases.
CLOSING PERMISSION LOGIC
If the voltage at one or both ends of the breaker is null, the synchrocheck function cannot
establish the necessary parameters to give conditions for closing, and therefore does not
issue synchrocheck permission. If the user wants to enable the closing permission for
cases where there is a of loss of one or both voltages at both ends of the breaker, the
synchrocheck function incorporates closing permission logic for the following cases.
•
Dead Line-Dead Bus,
•
Live Line-Dead Bus,
•
Dead Line-Live Bus,
•
Any Line-Dead Bus,
•
Dead Line-Any Bus,
•
One Live-Other Dead,
•
Not Both Live
LIVE LINE-LIVE BUS CONDITION
In the Live Line-Live Bus case, once the Voltage difference has been successfully verified in
magnitude, the relative frequency slip between phasors is calculated. From the
information obtained from the relay, the algorithm will kow the slip (mHz) of both phasors,
and it will take as reference (VRef) the lowest frequency phasor. The behavior of the
algorithm depends on the slip frequency and the breaker close time as follows:
1.
If the relative slip, ∆f, is equal to or lower than 20 mHz, the algorithm gives permission
to close as soon as the angle difference is lower than the
because at such a low speed, the hold time for getting an "in-phase" closing
permission would be too long.
2.
If the relative slip is higher than 30 mHz, the element performs an anticipative
algorithm, determining the right moment to give the closing command to the breaker,
so that the breaker closes when the line and busbar voltages are in phase. When the
difference between the voltage values equals two times the set angle as maximum
angle difference (∆V = ∆Vset), the anticipative algorithm starts running and uses the
set
Breaker Closing Time
in the moment when both voltage phasors are completely in phase, thus minimizing
the voltage difference in the breaker chamber to negligible values. The main benefit is
that after a considerable number of breaker operations, damage to internal
connection elements, as well as to the chamber isolating element, is drastically
reduced, ensuring a longer life for the breaker, and reducing costly maintenance
operations.
3.
The algorithm ensures that the difference between voltages in the real closing
moment it not higher than the set value (
PATH:
SETPOINTS > S4 CONTROLS > SYNCHROCHECK
SYNCHROCHECK FUNCTION:
Range: Disabled, Enabled
Default: Disabled
For details see
Common
to establish the initiation of permission, so that it is executed
Max Volt Diff
setpoints.
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
,
Max Angle Difference
).
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