9.5 Four step directional negative phase sequenceovercurrent protection NS4PTOC (46I2)9.5.1 IdentificationFunction description IEC 61850identificationIEC 60617 identification ANSI/IEEE C37.2device numberFour step negative sequenceovercurrent protectionNS4PTOC I244 altIEC10000053 V1 EN46I29.5.2 ApplicationFour step negative sequence overcurrent protection NS4PTOC (4612) is used in severalapplications in the power system. Some applications are:• Ground-fault and phase-phase short circuit protection of feeders in effectivelygrounded distribution and subtransmission systems. Normally these feeders haveradial structure.• Back-up ground-fault and phase-phase short circuit protection of transmission lines.• Sensitive ground-fault protection of transmission lines. NS4PTOC (4612) can havebetter sensitivity to detect resistive phase-to-ground-faults compared to distanceprotection.• Back-up ground-fault and phase-phase short circuit protection of powertransformers.• Ground-fault and phase-phase short circuit protection of different kinds of equipmentconnected to the power system such as shunt capacitor banks, shunt reactors andothers.In many applications several steps with different current pickup levels and time delays areneeded. NS4PTOC (4612) can have up to four, individual settable steps. The flexibility ofeach step of NS4PTOC (4612) function is great. The following options are possible:Non-directional/Directional function: In some applications the non-directionalfunctionality is used. This is mostly the case when no fault current can be fed from theprotected object itself. In order to achieve both selectivity and fast fault clearance, thedirectional function can be necessary. This can be the case for unsymmetrical faultprotection in meshed and effectively grounded transmission systems. The directionalnegative sequence overcurrent protection is also well suited to operate in teleprotectionSection 9 1MRK 506 369-UUS -Current protection522 Line distance protection REL670 2.2 ANSIApplication manual
