ABB RELION 620 Series Technical Manual page 767

1MAC504801-IB E
9.3.5
620 series ANSI
Technical Manual
Application
The main purpose of the synchrocheck function is to provide control over the closing of
the circuit breakers in power networks to prevent the closing if the conditions for
synchronism are not detected. This function is also used to prevent the reconnection of two
systems which are divided after islanding and a three-pole reclosing.
The Synchro check function block includes both the synchronism check function and the
energizing function to allow closing when one side of the breaker is dead.
Network and the generator running in parallel with the network are connected through the
line AB. When a fault occurs between A and B, the protection relay protection opens the
circuit breakers A and B, thus isolating the faulty section from the network and making the
arc that caused the fault extinguish. The first attempt to recover is a delayed autoreclosure
made a few seconds later. Then, the autoreclose function 79 gives a command signal to the
synchrocheck function to close the circuit breaker A. 25 performs an energizing check, as
the line AB is de-energized (V_BUS> Live bus value, V_LINE< Dead line value). After
verifying the line AB is dead and the energizing direction is correct, the protection relay
energizes the line (V_BUS -> V_LINE) by closing the circuit breaker A. The PLC of the
power plant discovers that the line has been energized and sends a signal to the other
synchrocheck function to close the circuit breaker B. Since both sides of the circuit
breaker B are live (V_BUS > Live bus value, V_LINE > Live bus value), the synchrocheck
function controlling the circuit breaker B performs a synchrocheck and, if the network and
the generator are in synchronism, closes the circuit breaker.
A
52
V_Bus
25
79
GUID-3C69BD5D-5D9F-44C7-87C8-D25C70829B97 V2 EN
Figure 390: Synchrocheck function 79 checking energizing conditions and
synchronism
V_Line V_Line
Section 9
Control functions
G
B
52
V_Bus
25
PLC
761