4.4.1.2
Function block
Figure 465: Function block
4.4.1.3
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.
4.4.1.4
Analog channel configuration
NSPTOC has one analog group input which must be properly configured.
Table 734: Analog signals
Input
Description
I3P
Three-phase currents
See the preprocessing function blocks in this document for the possible
signal sources.
Improper analog channel configuration causes a validation error if the analog
channels are not completely configured or they do not match with certain settings.
For troubleshooting, check the contents of this chapter and also the preprocessing
blocks in this document. The configuration can be written to the protection relay
once the mismatch is corrected.
4.4.1.5
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
Protection functions
1MRS759142 F
820
REX640
Technical Manual