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2.6
Negative Sequence Protection 46
Negative sequence protection detects unbalanced loads on the system.
Applications
• This protection function can be used to detect interruptions, short-circuits and polarity problems in the con-
nections to the current transformers.
• It also allows to detect single-phase and two-phase faults with fault currents smaller than the maximum load
current.
Prerequisites
The unbalanced load protection becomes effective when:
a minimum phase current is larger than 0.1 x I
all phase currents are smaller than 10 x I
2.6.1
Definite Time Characteristic
The definite time characteristic consists of two elements. As soon as the first settable threshold 46-1 PICKUP
is reached, a pickup message is output and time element 46-1 DELAY is started. When the second Element
46-2 PICKUP is started, another message is output and time element 46-2 DELAY is initiated. Once either
time delay elapses, a trip signal is initiated.
Figure 2-28
Definite time characteristic for negative sequence protection
Settable Dropout Times
Pickup stabilization for the definite-time tripping characteristic 46-1, 46-2 can be accomplished by means of set-
table dropout times. This facility is used in power systems with possible intermittent faults. Used together with
electromechanical relays, it allows different dropout responses to be adjusted and a time grading of numerical
and electromechanical relays to be implemented.
SIPROTEC, 7SC80, Manual
E50417-G1140-C486-A1, Release date 12.2011
and
Nom
.
Nom
Functions
2.6 Negative Sequence Protection 46
107
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