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1MRK 506 369-UEN B
Line distance protection REL670 2.2 IEC
Application manual
•
Earth-fault and phase-phase short circuit protection of feeders in effectively
earthed distribution and subtransmission systems. Normally these feeders have
radial structure.
•
Back-up earth-fault and phase-phase short circuit protection of transmission
lines.
•
Sensitive earth-fault protection of transmission lines. NS4PTOC can have
better sensitivity to detect resistive phase-to-earth-faults compared to distance
protection.
•
Back-up earth-fault and phase-phase short circuit protection of power
transformers.
•
Earth-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 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 36:
Inverse time characteristics
Curve name
ANSI Extremely Inverse
ANSI Very Inverse
ANSI Normal Inverse
ANSI Moderately Inverse
ANSI/IEEE Definite time
ANSI Long Time Extremely Inverse
Table continues on next page
Section 9
Current protection
489
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