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
connections to the current transformers.
•
It is also useful in detecting single-phase and two-phase faults with fault currents lower than the
maximum load currents.
Prerequisites
The unbalanced load protection becomes effective when:
at least one phase current is greater than 0.1 x Ι
Nom
and
all phase currents are smaller than 10 x Ι
Nom
.
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.
[unabhaeng-ausl_charakt-des-schieflastschutzes-260602-kn, 1, en_US]
Figure 2-48 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
settable 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.
Inverse Time characteristic
The inverse time element is dependent on the ordered device version. It operates with IEC or ANSI character-
istic tripping curves. The curves and associated formulas are given in the Technical Data. When programming
2.7
2.7.1
2.7.2
Functions
2.7 Negative Sequence Protection 46
132 SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
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