ABB REF615 - Functionality

5.3.1.2 Functionality
The negative phase-sequence current protection NSPTOC is used for increasing
sensitivity to detect single phasing situations, unbalanced loads due to, for example,
broken conductors or to unsymmetrical feeder voltages.
The function is based on the measurement of the negative phase-sequence current.
In a fault situation, the function starts when the negative phase sequence current
exceeds the set limit. The operate time characteristics can be selected to be either
definite time (DT) or inverse definite minimum time (IDMT). In the DT mode, the
function operates after a predefined operate time and resets when the fault current
disappears. The IDMT mode provides current dependent timer characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers, or the function itself, if desired.
5.3.1.3 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.
5.3.2 Phase discontinuity PDNSPTOC
5.3.2.1 Identification
Table 67: Function identification
IEC 61850 identification:
PDNSPTOC
IEC 60617 identification: I2/I1>
ANSI/IEEE C37.2 device number: 46PD
1MRS756378 D Section 5
Protection functions
REF615 159
Application Manual