2.Synchro-Check Function - ABB REX 521 Technical Reference Manual, Standard Configurations

REX 521
11.3.3.2.
182
Protection Relay
Technical Reference Manual, Standard Configurations
The time grading includes (definite time):
2 X Tolerance of the + Operation time
relays' operate times
As an example the time grading can be:
2 x 25 ms + 50 ms + 30 ms + 20 ms = 150 ms
Back-up protection can be realized with the circuit-breaker failure protection
function of the protection relay. A fast back-up function can be achieved because the
safety margin can be omitted when setting the CBFP time. The CBFP function
requires external wiring from the protection relay of the bus sectionalizer to the relay
of the in-feeder.
The settings for the overcurrent protections can be found in:
Main menu\Protection\3I>\ ... \3I>>>\Setting group 1\ where
the parameters "Operation mode", "Start current" and "Operate time" for the
function can be set. In Main menu\Protection\3I>\Control setting\
can for example the "Drop-off time" and the length of the trip signal "Trip pulse" be
set. The data of the three last operations, start or trip, are recorded and the values of
the most recent operation can be found in
Main menu\Protection\3I>\Recorded data1\...3\.
Synchro-check function
In this application example where the synchro-check function is used for ensuring
the condition between two busbar sections fed by own transformers, the voltage
difference between busbar sections is the most important criterion. The synchro-
check function does not allow the circuit breaker to be closed if the voltage
difference is too high. If the voltage difference is great, the inrush current between
the busbar sectors can be too high. In an application where a generator is connected
to one of the busbar sectors other criteria are also important and the need for the
synchro-check functionality is unavoidable.
The synchro-check function can be used in two different operating conditions. The
most typical case is one where both sides of the circuit breaker to be closed are live
and thus the synchronism is always checked before the circuit breaker is given the
permission to close. In an other situation one or both sides of the circuit breaker to
be closed are dead and, consequently, the frequency and phase differences cannot be
measured, in which case the relay checks the energizing direction.
Operation criteria of the function are:
• Voltages must be in accordance with the energizing direction.
• In cases "Live-Dead", "Dead-Live" and "Dead-Dead" no other conditions are
checked.
• In the case "Live-Live" also the following must be fulfilled:
∆
• U< dU setting
∆
• f< df setting
∆
ϕ< dphi setting
•
Before the function block allows the closing of the CB, it ensures that the phase
difference remains within the setting range until the CB closes.
+ Retardation time
of the CB of the relay
1MRS 751802-MUM
+ Saturation and delay
margin