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162
Synchro-check and energising-check
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The synchrocheck function is used for controlled closing of a circuit in an interconnect-
ed network. When used, the function gives an enable signal at satisfied voltage condi-
tions across the breaker to be closed. When there is a parallel circuit established, the
frequency is normally the same at the two sides of the open breaker. At power swings,
e.g. after a line fault, an oscillating difference can appear. Across the open breaker,
there can be a phase angle and a voltage amplitude difference due to voltage drop across
the parallel circuit or circuits. The synchro-check function measures the difference be-
tween the U-line and the U-bus, regarding voltage (UDiff), phase angle (PhaseDiff),
and frequency (FreqDiff). It operates and permits closing of the circuit breaker when
the following conditions are simultaneously fulfilled:
•
The voltages U-line and U-bus are higher than the set value for UHigh of the base
voltage U1b.
•
The differences in the voltage and phase angles are smaller than the set values of
UDiff and PhaseDiff.
•
The difference in frequency is less than the set value of FreqDiff. The bus frequency
must also be within a range of +/- 10 % of the rated frequency.
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The function can be used as a condition to be fulfilled before the breaker is closed at
manual closing and/or together with the auto-recloser function.
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