SIPROTEC 4 7SJ63 Multifunction Protection Relay - Siemens

5 Overcurrent Protection / 7SJ635Protection functionsDirectional time-overcurrent protection(ANSI 67, 67N)Directional phase and earth protection areseparate functions. They operate in parallelto the non-directional overcurrent elements.Their pickup values and delay times can beset separately. Definite-time and inverse-timecharacteristic is offered. The tripping characteristiccan be rotated about ± 180 degrees.By means of voltage memory, directionalitycan be determined reliably even for close-in(local) faults. If the switching device closesonto a fault and the voltage is too low to determinedirection, directio- nality (directionaldecision) is made with voltage fromthe voltage memory. If no voltage exists inthe memory, tripping occurs according tothe coordination schedule.For earth protection, users can choosewhether the direction is to be determined viazero-sequence system or negative-sequencesystem quantities (selectable). Using negative-sequencevariables can be advantageousin cases where the zero voltage tends to bevery low due to unfavorable zero-sequenceimpedances.Fig. 5/113Directional characteristic of thedirectional time-overcurrentprotectionDirectional comparison protection(cross-coupling)It is used for selective protection of sectionsfed from two sources with instantaneoustripping, i.e. without the disadvantage oftime coordination. The directional comparisonprotection is suitable if the distances betweenthe protection stations are not significantand pilot wires are available for signaltransmission. In addition to the directionalcomparison protection, the directional coordinatedtime-overcurrent protection is usedfor complete selective backup protection. Ifoperated in a closed-circuit connection, aninterruption of the transmission line is detected.(Sensitive) directional earth-fault detection(ANSI 64, 67Ns, 67N)For isolated-neutral and compensated networks,the direction of power flow in the zerosequence is calculated from the zero-sequencecurrent I 0 and zero-sequence voltage V 0.For networks with an isolated neutral, the reactivecurrent component is evaluated; forcompensated networks, the active currentcomponent or residual resistive current isevaluated. For special network conditions,5/122e.g. high-resistance earthed networks withohmic-capacitive earth-fault current orlow-resistance earthed networks withohmic-inductive current, the tripping characteristicscan be rotated approximately± 45 degrees.Two modes of earth-fault direction detectioncan be implemented: tripping or “signallingonly mode”.It has the following functions:• TRIP via the displacement voltage V E.• Two instantaneous elements or oneinstantaneous plus one user-definedcharacteristic.• Each element can be set in forward,reverse, or non-directional.• The function can also be operated in theinsensitive mode as an additionalshort-circuit protection.Fig. 5/114Directional determination usingcosine measurements forcompensated networks(Sensitive) earth-fault detection(ANSI 50Ns, 51Ns / 50N, 51N)For high-resistance earthed networks, a sensitiveinput transformer is connected to aphase-balance neutral current transformer(also called core-balance CT).The function can also be operated in theinsensitive mode as an additional shortcircuitprotection.Siemens SIP · 2006