ABB REL670 distance protection and troubleshooting

Common issues with Mho distance range. ZMHPDIS uses positive sequence polarized memory voltage, with directionality dependent on ZDRDIR. Mho circle relies on memory voltage to maintain direction judgment during near end three-phase faults; The memory voltage is generally maintained for 100ms. If the direction of the near end three-phase fault is reversed, check whether the ArgDir and ArgNegRes settings of ZDRDIR have been changed, and whether the polarization voltage meets the minimum threshold. The load intrusion of Mho characteristics is coordinated with FMPSPDIS. If the load intrusion is not configured correctly, the overloaded line may malfunction or refuse to operate.

Load intrusion is not a 'fault', but it will change the action boundary. When the transmission power of the line is high, the load impedance may enter the distance range action zone. REL670 uses the load intrusion characteristics of FDPSPDIS or FMPSPDIS to set blind spots in the resistance direction, avoiding the load impedance from being treated as a fault impedance. If there is a "distance segment start when the load increases" on site, the load intrusion resistance RLdFw/RLdRv and load angle ArgLd should be checked to see if they match the actual load, rather than simply increasing the distance segment resistance setting.

Directional and phase selection: hidden reasons for out of zone fault escalation

The direction determination of distance protection is completed by ZDRDIR, and the phase selection is completed by FDPSPDIS or FMPSPDIS. The two interact with the distance segment through binary encoded signals: STCND is the loop enable for the distance segment, and DIRCND is the directional condition. If these two signals are connected incorrectly or configured incorrectly, the distance segment may not move at all or move in the wrong direction.

Reverse direction investigation. First check CTStarPoint, then check the polarity setting of ZDRDIR, and finally check the phase sequence of voltage and current. For double circuit lines or parallel lines on the same tower, it is also necessary to check the zero sequence mutual inductance compensation and current reverse logic. If there is a fault outside the area and the local distance segment starts but the opposite side does not jump, the communication channel and enable/lock logic should be checked, rather than just changing the time setting.

Troubleshooting of phase selection errors. The STCNDZ output of FDPSPDIS is used for quadrilateral distance segments, while STCNDLE is used for load only intrusion conditions. If the phase selection classifies a single-phase grounding fault as a three-phase fault, the recloser will trip according to the three-phase, causing the single-phase recloser to fail. The zero sequence current threshold INRelease PE, INBlockPP, negative sequence voltage threshold U2MinOp, positive sequence voltage threshold U1MinOP, and other settings should be checked, and combined with waveform recording to view the current, voltage, and sequence components before and after the fault.

Locking of power swing, load intrusion, and distance protection

REL670's ZMRPSB is used for power swing detection, while ZMRPSL is used for power swing logic. When the power swings, the impedance trajectory will pass through the action zone of the distance range. If it is not locked, the distance protection may malfunction. When there is a "distance protection trip during system oscillation" on site, it is necessary to check whether ZMRPSB is activated, whether the internal and external quadrilateral boundaries, tP1/tP2/tW/tH time settings are reasonable, and whether ZMRPSL's locking and permission logic is correct.

Power swing detection relies on impedance change speed. If tP1 is set too small, the fault may be mistaken for swing; If tP2 is set too large, it may be considered a malfunction due to swinging. The impedance trajectory and current change rate in the disturbance recording should be combined for verification. For heavy-duty lines, load intrusion and power swing may coexist, and the load intrusion characteristics of FDPSPDIS and the swing boundary of ZMRPSB should be checked separately to avoid mutual interference between the two.

Recloser and fault location: "result verification" after troubleshooting

REL670 supports SMBRREC automatic reclosing up to five times, supports single-phase, two-phase, and three-phase reclosing, and can be synchronized with SESRSYN for inspection. If the reclosing is unsuccessful, one should first distinguish between "protection not issuing reclosing command", "reclosing locked", "circuit breaker not closed", and "tripping again after closing".

Common reasons for unsuccessful reclosing. Check if CBREADY meets the requirements, if CBPOS was closed before the fault, if INHIBIT was locked by external signals, if SYNC is met within tSync, and if the reclosing method matches the fault type. When a single-phase fault occurs, if the protection triggers a three-phase trip, the reclosing will not operate in a single-phase manner; The program settings and phase selection output of SMPPTRC should be checked. After reclosing and tripping again, the fault recording should be checked to determine whether it is a permanent fault or a reclosing fault.