ABB Relion 620 Series - Page 612

The Blocking mode setting has three blocking methods. In the "Freeze timers"
mode, the operation timer is frozen to the prevailing value, but the OPERATE output
is not deactivated when blocking is activated. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the OPERATE output is not activated.
4.4.1.5 Application
Since the negative sequence current quantities are not present during normal,
balanced load conditions, the negative sequence overcurrent protection elements
can be set for faster and more sensitive operation than the normal phase-
overcurrent protection for fault conditions occurring between two phases. The
negative sequence overcurrent protection also provides a back-up protection
functionality for the feeder earth-fault protection in solid and low resistance
earthed networks.
The negative sequence overcurrent protection provides the back-up earth-fault
protection on the high voltage side of a delta-wye connected power transformer
for earth faults taking place on the wye-connected low voltage side. If an earth fault
occurs on the wye-connected side of the power transformer, negative sequence
current quantities appear on the delta-connected side of the power transformer.
The most common application for the negative sequence overcurrent protection is
probably rotating machines, where negative sequence current quantities indicate
unbalanced loading conditions (unsymmetrical voltages). Unbalanced loading
normally causes extensive heating of the machine and can result in severe damages
even over a relatively short time period.
Multiple time curves and time multiplier settings are also available for coordinating
with other devices in the system.
4.4.1.6 Signals
Table 539: NSPTOC Input signals
Name Type Default Description
I
2
SIGNAL 0 Negative phase sequence current
BLOCK BOOLEAN 0=False Block signal for activating the
blocking mode
ENA_MULT BOOLEAN 0=False Enable signal for current multiplier
Table 540: NSPTOC Output signals
Name Type Description
OPERATE BOOLEAN Operate
START BOOLEAN Start
Protection functions 1MRS757644 H
612 620 series
Technical Manual