ABB SPAC 536 C User Manual page 98

Earth-fault unit
Circuit breaker
failure protection
Remote settings
4
The non-directional earth-fault unit of the
module SPCJ 4D24 is a single-pole neutral cur-
rent or residual current overcurrent unit. It con-
tains two neutral overcurrent stages, i.e. a low-
set overcurrent stage I
0
current stage I >>.
0
The low-set or high-set overcurrent stage starts
if the current to be measured exceeds the set-
ting value of the stage concerned. When start-
ing, the stage provides a starting signal SS1 or
TS1 and simultaneously the operation indica-
tor on the front panel indicates starting. If the
earth-fault situation lasts long enough to exceed
the set operating time, the stage that started calls
for a C.B. tripping by providing a tripping sig-
nal TS2. At the same time the red operation
indicator of the tripping stage goes on. The
operation indicator remains on although the
stage resets. The indicator is reset with the RE-
SET push-button.
The neutral current measured by the earth-fault
unit is filtered in a low-pass filter which effec-
tively reduces the amount of harmonics in the
measured signal. For example the third harmon-
ics is reduced to about ten percent of its origi-
nal value by the filter. Higher order harmonics
are reduced even more.
The operation of the low-set overcurrent stage
I > or the high-set stage I
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applying a blocking signal BS onto the stage.
The blockings are programmed by means of
switchgroup SGB on the front of the plug-in
module.
The unit is also provided with a circuit breaker
failure protection (CBFP), which gives a trip
signal via TS1 within a set time 0.1...1 s after
the normal trip signal TS2, if the fault has not
been cleared within that time. The output con-
tact of the circuit breaker failure protection is
normally used for tripping an upstream circuit
breaker. The CBFP can also be used to estab-
All the main setting values may be provided with
alternative setting values that can be called up
by remote control. The switching between main
and remote settings is normally made by utiliz-
ing the serial communication link. If the serial
> and a high-set over-
>> can be blocked by
0
The operation of the low-set neutral current
stage I > is based on a definite time character-
0
istic. The operating time t
the setting range 0.05...300 s.
The operating time t >> of the high-set current
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stage is set separately within the range 0.05...
300 s.
The operation of the two neutral overcurrent
stages is provided with a latching facility (switch
SGB/7) keeping the tripping output energized,
although the signal which caused the operation
disappears. The stages are reset by simultane-
ous pressing of the push-buttons RESET and
PROGRAM, see section "Programming switches".
The operation of the high-set earth-fault stage
may be inhibited when connecting the pro-
tected object to the network, i.e. when the low-
set stage of the overcurrent unit is started. Thus
it is possible to avoid malfunction due to vir-
tual earth-fault currents caused by current trans-
former anomalies in connection with the con-
nection inrush current. The automatic inhibit-
ing function is selected with switch SGF1/6.
The operation of the high-set earth-fault stage
I >> may be totally blocked by means of switch
0
SGF2/6. When the high-set stage is set out of
operation, the display shows a "- - -" readout,
indicating that the setting value is infinite.
lish a redundant trip system by using dual trip
coils on the circuit breaker and wiring one of
them to TS2 and the other one to TS1. The
circuit breaker failure protection is selected by
means of switch SGF1/4. The setting of the time
delay can be made using submenu position five
in register A.
communication is not used, the control input
signal BS can be programmed to perform the
switching too. Finally manual switching be-
tween setting banks can be made using submenu
position four in register A.
> can be set within
0