SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 46 of 74
by the A or B phases of the transmission line being de-energised. This inhibition
is brought about by the action of the low set current level detector LDLSA and
LDLSB.
To extend this period of non operation to the first 240ms after the line is
re-energised, the “ANY POLE DEAD” signal is used. The pole dead A (PdA) and
pole dead B (PdB) signals also inhibit the Zone 6 A–B comparator.
2) When a signal is received from the auto reclose unit via the inhibit power swing
blocking opto isolator, signifying that the distance relay has tripped, but the
circuit breaker has not yet reclosed, that is, dead time is in progress.
This inhibition of the PSB feature ensures that if a power swing develops during
the dead time of a single phase auto reclose cycle, the distance relay can give
an immediate three phase trip.
3) When the low set neutral current level detector LDLSN operates. This level
detector remains unoperated during balanced power swing conditions, but can
operate to prevent incorrect PSB operation under the following conditions:
i) if a ground fault occurs during a power swing.
ii) if a heavy ground fault occurs such that the impedance seen by the A–B
comparators lies between the boundaries of Zone 6 and Zone 3.
iii) if a power swing develops during the dead time of a single phase auto
reclose cycle.
4) Under conditions of loss of a voltage supply, provided that the voltage
transformer supervision feature has been set to indicate and block the relay
(SW3 in right hand position).
Operation of the PSB feature is indicated by the relevant LED on the scheme logic
module and an output contact (95–1) is provided to give a remote alarm of a
power swing condition. The indication logic (see Section 6.41) latches the PSB
indication. This may be reset by operating the reset button on the scheme logic
module.
Two test points (SK PS and SK TPS) are provided on test socket SK2 of the auxiliary
relay module, to allow thorough testing of the Zone 6 comparator and the PSB
logic.
5.14 Current input circuits
A novel electro-magnetic coupling device known as the transphasor is used for
each current input circuit of Quadramho. This circuit produces the
IZ vectors for
each phase and for the neutral, as required by the comparators and level
detectors.
The transphasor is based on the summation of two magnetic fluxes. One flux is
fixed phase and amplitude while the other flux is variable in both phase and
amplitude. The variable flux originates from the current flowing in a constant
inductance and variable resistance circuit, following a semicircular locus as the
resistance is changed from infinity to zero.
When the two fluxes are added, the total flux phasor also follows a semicircular
locus. If the magnitude of the fixed flux phasor is made equal to the radius of the
variable flux locus, the total flux phasor forms the radius of this new semicircle.
Hence the magnitude of the total flux remains constant as its phase angle is varied
over 180°.
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