ABB RELION 670 Series Applications Manual page 127

Phasor measurement unit version 2.1 ansi
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1MRK 511 364-UUS A
Ground-fault and phase-phase short circuit protection of feeders in effectively grounded
distribution and subtransmission systems. Normally these feeders have radial structure.
Back-up ground-fault and phase-phase short circuit protection of transmission lines.
Sensitive ground-fault protection of transmission lines. NS4PTOC (4612) can have better
sensitivity to detect resistive phase-to-ground-faults compared to distance protection.
Back-up ground-fault and phase-phase short circuit protection of power transformers.
Ground-fault and phase-phase short circuit protection of different kinds of equipment
connected to the power system such as shunt capacitor banks, shunt reactors and others.
In many applications several steps with different current pickup levels and time delays are needed.
NS4PTOC (4612) can have up to four, individual settable steps. The flexibility of each step of
NS4PTOC (4612) 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
grounded 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 15:
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
Table continues on next page
Application manual
Inverse time characteristics
Section 8
Current protection
121

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