4.3.1.2 Function block
Figure 204: Function block
4.3.1.3 Functionality
The negative-sequence overcurrent protection function NSPTOC is used for
increasing sensitivity to detect single-phase and phase-to-phase faults or
unbalanced loads due to, for example, broken conductors or unsymmetrical feeder
voltages.
NSPTOC can also be used for detecting broken conductors.
The function is based on the measurement of the negative sequence current. In
a fault situation, the function starts when the negative 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.
4.3.1.4 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of NSPTOC can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 205: Functional module diagram
Level detector
The measured negative-sequence current is compared to the set
Start value
. If the
measured value exceeds the set
Start value
, the level detector activates the timer
Protection functions
1MRS758755 C
410 REC615 & RER615
Technical Manual
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