Synchrocheck - ABB 650 series Applications Manual

1MRK 511 423-UEN A
8.1.2.2
Bay control REC650 2.2 IEC
Application manual

Synchrocheck

The main purpose of the synchrocheck function is to provide control over the
closing of circuit breakers in power networks in order to prevent closing if
conditions for synchronism are not detected. It is also used to prevent the re-
connection of two systems, which are divided after islanding and after a three pole
reclosing.
Single pole auto-reclosing does not require any synchrocheck since
the system is tied together by two phases.
SESRSYN function block includes both the synchrocheck function and the
energizing function to allow closing when one side of the breaker is dead.
SESRSYN function also includes a built in voltage selection scheme which allows
adoption to various busbar arrangements.
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IEC04000179 V1 EN-US
Figure 30: Two interconnected power systems
Figure 30 shows two interconnected power systems. The cloud means that the
interconnection can be further away, that is, a weak connection through other
stations. The need for a check of synchronization increases if the meshed system
decreases since the risk of the two networks being out of synchronization at manual
or automatic closing is greater.
The synchrocheck function measures the conditions across the circuit breaker and
compares them to set limits. Output is generated only when all measured
conditions are within their set limits simultaneously. The check consists of:
• Live line and live bus.
• Voltage level difference.
• Frequency difference (slip). The bus and line frequency must also be within a
range of ±5 Hz from rated frequency.
• Phase angle difference.
A time delay is available to ensure that the conditions are fulfilled for a minimum
period of time.
In very stable power systems the frequency difference is insignificant or zero for
manually initiated closing or closing by automatic restoration. In steady conditions
a 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 synchrocheck
Section 8
Control
M12309-6 v10
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