ABB REG670 Applications Manual page 487

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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
Figure 223: Two interconnected power systems
Figure 223 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 with a
long operation time and high sensitivity regarding the frequency difference. The phase
angle difference setting can be set for steady state conditions.
Another example is the operation of a power network that is disturbed by a fault event:
after the fault clearance a highspeed auto-reclosing takes place. This can cause a
Section 15
Control
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