Capacitive Voltage Transformers Supervision (Cvts); Output Ddb Used In The Psl; Check Synchronisation; Basic Cvt Supervision Diagram - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-142
The residual voltage setting, CTS VN< Inhibit and the residual current setting, CTS IN> set,
should be set to avoid unwanted operation during healthy system conditions. For example
CTS VN< Inhibit should be set to 120% of the maximum steady state residual voltage. The
CTS IN> set will typically be set below minimum load current. The time-delayed alarm,
CTS Time delay, is generally set to 5 seconds.
Where the magnitude of residual voltage during an earth fault is unpredictable, the element
must be disabled to prevent a protection elements being blocked during fault conditions.
The DDB: 'CT Fail Alarm' output is associated to CTS in the PSL (see section P44x/EN PL).
5.8.3

Capacitive Voltage Transformers Supervision (CVTS)

5.8.3.1 Function description
This Capacitive Voltage Transformers (CVT) Supervision will detect the degradation of one
or several capacitors of voltage dividers. It is based on permanent detection of residual
voltage.
A "CVT fault" signal is sent out, after a settable time-delay if the conditions are as follows:
• The residual voltage is greater than the setting threshold
• The 3 phase-phase voltages have a value greater than 0.4 Un
• If CVTS V2 Status > is set to Enabled and the negative sequence voltage is
greater than setting CVTS V2>
Vab(t)
Vbc(t)
Vca(t)
Vr(t)
Va
Formatting
Vb
of analogue
quantities
Vc
Figure 103: Basic CVT supervision diagram
5.8.3.2

OUTPUT DDB used in the PSL

The DDB: 'CVT ALARM' is associated to CVTS in the PSL (see section P44x/EN PL).
5.9

Check synchronisation

The check synchronism option is used to qualify reclosure of the circuit breaker so that it can
only occur when the network conditions on the busbar and line side of the open circuit
breaker are acceptable. If a circuit breaker were closed when the two system voltages were
out of synchronism with one another, ie. a difference in voltage magnitudes or phase angles
existed, the system would be subjected to an unacceptable 'shock', resulting in loss of
stability and possible damage to connected machines.
Check synchronism therefore involves monitoring the voltage on both sides of a circuit
breaker and, if both sides are 'live', the relative synchronism between the two supplies. Such
checking may be required to be applied for both automatic and manual reclosing of the
circuit breaker and the system conditions which are acceptable may be different in each
case. For this reason, separate check synchronism settings are included within the relay for
both manual and automatic reclosure of the circuit breaker. With manual closure, the CB
Vab(t) > 0,8*Vn
S
Q
R
Vab(t) < 0,4*Vn
Vbc(t) > 0,8*Vn
S
Q
R
Vbc(t) < 0,4*Vn
Vca(t) > 0,8*Vn
S
Q
R
Vca(t) < 0,4*Vn
Vr(t) > SVr
CVTS V2>
&
CVTS V2 Status>
Enabled
MiCOM P40 Agile P442, P444
&
CVTS V2 Status>
OR
Disabled
&
Application Notes
&
CVTS Alarm
t
OR
0
CVTS Time Delay
3 P 10 ENc 2