7SR210 & 7SR220 Description of Operation
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4.9.7 System Synchronising Mode
For the relay to issue a System Sync Close the following conditions have to be met: -
Both the Bus and Line voltages must be considered Live by the Voltage Monitoring elements.
25 System Sync Angle – the phase difference between the line and bus voltages has to be less than the phase
angle setting value and the phase angle has to be decreasing before the element will issue a valid close signal.
25 System Sync Slip, [if Enabled] – the frequency difference between line and bus has to be less than the slip
frequency setting value. Slip frequency must be above the 25 Split Slip setting to avoid reversion to Check
Synchronising conditions. The settings for 25 System Sync Slip and 25 Split Slip must differ by at least 20 mHz.
25 System Sync Timer, [if Enabled] – the phase angle and voltage blocking features have to be within their
parameters for the length of the slip timer setting. If either the phase angle or the voltage elements fall outside of
their limits the slip timer is reset. If they subsequently come back in then the slip timer has to time out before an
output is given. (This ensures that a close output will not be given if there is a transient disturbance on the
system due to e.g. some remote switching operations).
25 Line Undervolts, [if Enabled] – the line voltage has to be above the line under-voltage setting value and also
above 5V for an output to be given.
25 Bus Undervolts, [if Enabled] – the bus voltage has to be above the line under-voltage setting value and also
above 5V for an output to be given.
25 Volt Differential, [if Enabled] – the difference between the line and bus voltages has to be less than the V
detector setting value for an output to be given.
The System Synchronising operation of the relay will only be started after a System Split is detected as described
in section 4.9.6 during an autoreclose or manual close sequence.
Phase Within Range ?
AND
Phase Decreasing ?
SLIP
Line U/V
Block
Bus U/V
BLock
V Block
D
Phase Angle Setting
&
Slip Frequency Setting
Block
Block
Block
&
Slip Timer
Setting
Slip Timer
F
Angle
Slip Within Range ?
SystemSync
Close
Live Line
Live Bus
Figure 4.9.7-1 System Sync Function
4.9.8 Close on Zero Mode
If the 25 DAR Split Mode or 25 MC Split Mode is set to COZ the relay will apply a Close-On-Zero to the respective
closing operation if the synchronising mode changes to System Split. The measured slip frequency and the
measured phase difference are used to provide a Close Pulse which will close the CB when the phase difference
is reducing and timed with the setting 25 CB Close Time such that the instant of closure is when the phase
difference is zero. The slip frequency must be less than the 25 COZ Slip Freq but greater than the 25 Split Slip
setting to avoid reversion to Check Synchronising conditions.
Since this feature is part of the System Synchronising function, 25 System Sync must also be set to Enabled.
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