ABB Relion REC670 Applications Manual page 135

1MRK 511 358-UEN A
In many applications several steps with different current operating levels and time delays are
needed. NS4PTOC can have up to four, individual settable steps. The flexibility of each step of
NS4PTOC function is great. The following options are possible:
Non-directional/Directional function: In some applications the non-directional functionality is
used. This is mostly the case when no fault current can be fed from the protected object itself.
In order to achieve both selectivity and fast fault clearance, the directional function can be
necessary. This can be the case for unsymmetrical fault protection in meshed and effectively
earthed transmission systems. The directional negative sequence overcurrent protection is
also well suited to operate in teleprotection communication schemes, which enables fast
clearance of unsymmetrical faults on transmission lines. The directional function uses the
voltage polarizing quantity.
Choice of time characteristics: There are several types of time characteristics available such as
definite time delay and different types of inverse time characteristics. The selectivity between
different overcurrent protections is normally enabled by co-ordination between the operating
time of the different protections. To enable optimal co-ordination all overcurrent relays, to be
co-ordinated against each other, should have the same time characteristic. Therefore a wide
range of standardized inverse time characteristics are available: IEC and ANSI.
Table 17:
Curve name
ANSI Extremely Inverse
ANSI Very Inverse
ANSI Normal Inverse
ANSI Moderately Inverse
ANSI/IEEE Definite time
ANSI Long Time Extremely Inverse
ANSI Long Time Very Inverse
ANSI Long Time Inverse
IEC Normal Inverse
IEC Very Inverse
IEC Inverse
IEC Extremely Inverse
IEC Short Time Inverse
IEC Long Time Inverse
IEC Definite Time
User Programmable
ASEA RI
RXIDG (logarithmic)
There is also a user programmable inverse time characteristic.
Normally it is required that the negative sequence overcurrent function shall reset as fast as
possible when the current level gets lower than the operation level. In some cases some sort of
delayed reset is required. Therefore different kinds of reset characteristics can be used.
For some protection applications there can be a need to change the current operating level for
some time. Therefore there is a possibility to give a setting of a multiplication factor
the negative sequence current pick-up level. This multiplication factor is activated from a
binary input signal ENMULTx to the function.
Application manual
Inverse time characteristics
Section 7
Current protection
IxMult to
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