Application - ABB RELION REX640 Technical Manual

Section 9
Control functions
9.5.6
1394
The vector group of the power transformer is defined with clock numbers, where the
value of the hour pointer defines the low-voltage-side phasor and the high-voltage-
side phasor is always fixed to the clock number 12, which is same as zero. The angle
between clock numbers is 30 degrees. When comparing phase angles, the U_BUS
input is always the reference. This means that when the Yd11 power transformer is
used, the low-voltage-side voltage phasor leads by 30 degrees or lags by 330 degrees
the high-voltage-side phasor. The rotation of the phasors is counterclockwise.
The generic rule is that a low-voltage-side phasor lags the high-voltage-side phasor by
clock number * 30º. This is called angle difference adjustment and can be set for
SECRSYN with the Phase shift setting.

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
DARREC gives a command signal to the synchrocheck function to close the circuit
breaker A. SECRSYN performs an energizing check, as the line AB is de-energized
(U_BUS> Live bus value, U_LINE< Dead line value). After verifying the line AB is
dead and the energizing direction is correct, the protection relay energizes the line
(U_BUS -> U_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
(U_BUS > Live bus value, U_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.
1MRS759142 C
REX640
Technical Manual