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 358: 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 359: NSPTOC Output signals
Name
Type Description
OPERATE BOOLEAN Operate
START BOOLEAN Start
1YHT530004D05 D Section 4
Protection functions
615 series 449
Technical Manual
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