9.4.2 USE OF CHECK SYNC 2 AND SYSTEM SPLIT
Check Sync 2 (CS2) and System Split functions are included for situations where the maximum permitted slip
fr
equency and phase angle for synchr
onism checks can change due to adverse system conditions. A typical
application is on a closely interconnected system, where synchronism is normally retained when a feeder is
tripped. But under some circumstances, with parallel interconnections out of service, the feeder ends can drift out
of synchronism when the feeder is tripped. Depending on the system and machine characteristics, the conditions
for safe circuit breaker closing could be, for example:
Condition 1: For synchronized systems, with zero or very small slip:
● Slip <50 mHz; phase angle <30°
Condition 2: For unsynchronized systems, with significant slip:
● Slip < 250 mHz; phase angle <10° and decreasing
By enabling both CS1 and CS2, the device can be configured to allow CB closure if either of the two conditions is
detected.
For manual circuit breaker closing with synchronism check, some utilities might prefer to arrange the logic to
check initially for condition 1 only. However, if a System Split is detected before the condition 1 parameters are
satisfied, the device will switch to checking for condition 2 parameters instead, based on the assumption that a
significant degree of slip must be present when system split conditions are detected. This can be arranged by
suitable PSL logic, using the System Check DDB signals.
9.4.3 PREDICTIVE CLOSURE OF CIRCUIT BREAKER
The setting CS2 Slip Contr
ol
setting contains an option (freq + CB comp) for compensating the time taken to close
the CB. When set to provide CB Close Time compensation, a predictive approach is used to close the circuit
breaker ensuring that closing occurs at close to 0º therefore minimising the impact to the power system. The
actual closing angle is subject to the constraints of the existing product architecture, i.e. the protection task runs
twice per power system cycle, based on frequency tracking over the frequency range of 40 Hz to 70 Hz.
9.4.4 VOLTAGE AND PHASE ANGLE CORRECTION
For the Check Synchronisation function, the device needs to convert measured secondary voltages into primary
v
oltages. In some applications, V
Ts either side of the circuit breaker may have different VT Ratios. In such cases, a
magnitude correction factor is required.
There are some applications where the main VT is on the HV side of a transformer and the Check Sync VT is on the
LV side, or vice-versa. If the vector group of the transformer is not "0", the voltages are not in phase, so phase
correction is also necessary.
The correction factors are as follows and are located in the CT AND VT RATIOS column:
● C/S V kSM, where kSM is the voltage correction factor.
● C/S Phase kSA, where kSA is the angle correction factor.
Assuming C/S input setting is A-N, then:
The line and bus voltage magnitudes are matched if V
a sec
= V
cs sec
x C/S V kSA
The line and bus voltage angles are matched if ÐV
a sec
= ÐV
cs sec
+ C/S Phase kSA
The following application scenarios show where the voltage and angular correction factors are applied to match
different VT ratios:
Scenario
Physical Ratios (ph-N Values) Setting Ratios CS Correction Factors
Main VT Ratio CS VT Ratio
Main VT Ratio (ph-
ph) Alw
ays
CS V
T Ratio
kSM kSA
Pri (kV) Sec (V) Pri (kV) Sec (V) Pri (kV) Sec (V) Pri (kV) Sec (V)
P14x Chapter 14 - Monitoring and Control
P14xEd1-TM-EN-1 335
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