ABB RELION REX640 Technical Manual page 820

Protection and control

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Protection functions

Function block

Figure 465: Function block

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

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.

Analog channel configuration

NSPTOC has one analog group input which must be properly configured.

Table 734: Analog signals

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.

Operation principle

The function can be enabled and disabled with the

corresponding parameter values are "On" and "Off".

NSPTOC can also be used for detecting broken conductors.

See the preprocessing function blocks in this document for the possible

signal sources.

Three-phase currents

Operation setting. The

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