GE P4A Technical Manual Download

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The Check Sync VT may be connected to one of the phase-to-phase voltages or phase-to-neutral voltages. This
needs to be defined using the CS Input setting in the CT AND VT RATIOS column. Options are, A-B, B-C, C-A, A-N, B-
N, or C-N.

9.1.2

VOLTAGE MONITORING

The settings in the VOLTAGE MONITORS sub-heading in the SYSTEM CHECKS column allow you to define the
threshold at which a voltage is considered live, and a threshold at which the voltage is considered dead. These
thresholds apply to both line and bus sides. If the measured voltage falls below the Dead Voltage setting, a DDB
signal is generated (Dead Bus, or Dead Line, depending on which side is being measured). If the measured voltage
exceeds the Live Voltage setting, a DDB signal is generated (Live Bus, or Live Line, depending on which side is
being measured).

9.1.3

CHECK SYNCHRONISATION

The device provides two stages of Check Synchronisation. The first stage (CS1) is intended for use in synchronous
systems. This means, where the frequencies and phase angles of both sides are compared and if the difference is
within set limits, the circuit breaker is allowed to close. The second stage (CS2) is similar to stage, but has an
additional adaptive setting. The second stage CS2 is intended for use in asynchronous systems, i.e. where the two
sides are out of synchronism and one frequency is slipping continuously with respect to another. If the closing time
of the circuit breaker is known, the CB Close command can be issued at a definite point in the cycle such that the
CB closes at the point when both sides are in phase.

In situations where it is possible for the voltages on either side of a circuit breaker to be either synchronous or
asynchronous, both CS1 and CS2 can be enabled to provide a CB Close signal if either set of permitted closing
conditions is satisfied.

Each stage can also be set to inhibit circuit breaker closing if selected blocking conditions such as overvoltage,
undervoltage or excessive voltage magnitude difference are detected. CS2 requires the phase angle difference to
be decreasing in magnitude before permitting the circuit breaker to close. CS2 has an optional “Adaptive” closing
feature, which issues the permissive close signal when the predicted phase angle difference immediately prior to
the instant of circuit breaker main contacts closing (i.e. after CB Close time) is as close as practicable to zero.

Slip frequency is the rate of change of phase between each side of the circuit breaker, which is measured by the
difference between the voltage signals on either side of the circuit breaker.

Having two system synchronism check stages available allows the circuit breaker closing to be enabled under
different system conditions (for example, low slip / moderate phase angle, or moderate slip / small phase angle).

The settings specific to Check Synchronisation are found under the sub-heading CHECK SYNC in the SYSTEM
CHECKS column. The only difference between the CS1 settings and the CS2 settings is that CS2 has a CS2 Adaptive
setting for predictive closure of CB.

9.1.4

CHECK SYNCRONISATION VECTOR DIAGRAM

The following vector diagram represents the conditions for the System Check functionality. The Dead Volts setting
is represented as a circle around the origin whose radius is equal to the maximum voltage magnitude, whereby
the voltage can be considered dead. The nominal line voltage magnitude is represented by a circle around the
origin whose radius is equal to the nominal line voltage magnitude. The minimum voltage magnitude at which the
system can be considered as Live, is the magnitude difference between the bus and line voltages.

GE P4A, Technical Manual

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