ABB SPAJ 141 C User Manual And Technical Description page 35

Earth-fault unit
The non-directional earth-fault unit of the module SPCJ 4D24 is a single-pole neutral current or residual
current overcurrent unit. It contains two neutral overcurrent stages, i.e. a low-set overcurrent stage I
a high-set overcurrent stage I
The low-set or high-set overcurrent stage starts if the current to be measured exceeds the setting value of the
stage concerned. When starting, the stage provides a starting signal SS1 or TS1 and simultaneously the
operation indicator 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 signal 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 RESET push-button.
The neutral current measured by the earth-fault unit is filtered in a low-pass filter which effectively reduces
the amount of harmonics in the measured signal. For example the third harmonics by the filter reduced to
about ten per cent of its original value. Higher order harmonics are reduced even more.
The operation of the low-set overcurrent stage Io> or the high-set stage Io>> can be blocked by 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 operation of the low-set neutral current stage I
time t > can be set within the setting range 0.05...300 s.
o
The operating time t
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 simultaneous 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 protected object to the
network, i.e. when the low-set stage of the overcurrent unit is started. Thus it is possible to avoid maloperations
due to virtual earth-fault currents caused by current transformer anomalies in connection with the connection
inrush current. The automatic inhibiting function is selected with switch SGF1/6.
The operation of the high-set earth-fault stage Io>> may be totally blocked by means of switch SGF2/6. When
the high-set stage is set out of operation, the display shows a "---" readout, indicating that the setting value
is infinite.
Circuit breaker failure protection
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
contact of the circuit breaker failure protection is normally used for tripping an upstream circuit breaker. The
CBFP can also be used to establish 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.
Remote settings
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 alternative settings is normally made by utilizing the serial
communication link. If the serial communication is not used, the control input signal BS can be programmed
to perform the switching too. Finally manual switching between setting banks can be made using submenu
position four in register A.
PAINOS PAINOS
>>.
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>> of the high-set current stage is set separately within the range 0.05...300 s.
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> is based on a definite time characteristic. The operating
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3
> and
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