ABB SPAC 531 C User Manual And Technical Description page 26

26
When a short circuit occurs in the protected
feeder, the overcurrent module records the
current value at the moment of tripping and
indicates the faulty phases. The current level
shows how distant the fault is and the type of
fault, that is, whether it is a two-phase or three-
phase fault.
The recorded values can also be used to verify
the correctness of the setting values. In a fault
situation the correspondence between the relay
settings and the actual currents can be verified.
In the same way a comparison of the setting
values and the values during normal operation is
allowed. The length of the starting signal of the
relay indicates the duration of a connection
inrush current.
The neutral overcurrent relay module U2 (SPCS
3C4) operates as a directional dual-stage earth-
fault protection of the outgoing feeder. In the
application illustrated in Fig 11, where the
earth-fault relay module has a tripping function,
the SGR/3 switch of the I/O module has to be
in position 1.
Current
Setting I ϕ >
CB position
I ϕ > start =
SIGNAL 4
output and
AR 3 signal
I ϕ > trip =
TRIP output
I ϕ > alarm =
SIGNAL 2
output
CB OPEN
output
CB CLOSE
output
Fig. 12. Signal diagram for an auto-reclose sequence initiated by starting of the Iϕ> stage.
The low-set stage of the earth-fault relay module
is set low enough to fulfil the sensitivity require-
ments of the safety regulations. The require-
ments concerning operate times are basically
fulfilled by the operate time of the high-set
stage.
The neutral overcurrent module can be used in
networks with resonant earthed, resistively
earthed and isolated neutrals.
When an earth fault occurs on the protected
feeder, the level of the neutral current is re-
corded by the earth-fault relay module. The
residual voltage is recorded by the relay module
monitoring the residual voltage of the measur-
ing cubicle. The degree of development of the
earth fault can be determined on the basis of
these values.
The control module U4 (SPTO 6D3) includes
an auto-reclose function carrying out the auto-
reclose functions required on the feeder. In this
example the AR starts are initiated by starting of
the neutral overcurrent or the phase overcurrent
module. The scheme in Fig. 12 shows the signals
and their time interdependence.
CLOSE
OPEN
ON
OFF
ON
OFF
ON
OFF
S25
ON
OFF
S26
ON
OFF
HSAR
(1st AR)
t
t>
S35
S36
Final trip
DAR
(2nd AR)