ABB REL670 distance protection and troubleshooting

ABB REL670 distance protection and troubleshooting

Introduction: Why can't we just look at the fixed value for distance protection and obstacle removal

ABB REL670 is a line distance protection IED in the RELION 670 series, aimed at transmission lines and secondary transmission lines, providing multi segment distance protection, directional overcurrent, ground fault protection, reclosing, synchronous inspection, fault location, disturbance recording, and IEC 61850 communication functions. When there is a "distance protection misoperation", "out of zone fault tripping", "unsuccessful reclosing", or "large fault distance measurement deviation" on site, many engineers' first reaction is to check the set value, but the real cause is often CT/VT polarity, voltage circuit, direction setting, load intrusion, power swing lockout, or communication channel.

The distance protection of REL670 adopts a full scheme measurement, with each segment containing three phase to ground circuits and three phase to phase circuits. Quadrilateral and Mho characteristics are optional, with a maximum of five segments. It supports load intrusion, power swing detection, fault phase selection, adaptive load compensation, fault location, and single-phase reclosing. When troubleshooting, the order of "checking the analog input and direction first, then checking the distance element and phase selection, and finally emphasizing the closing, recording, and communication" should be followed, rather than repeatedly modifying the impedance setting.

First check the analog input: CT/VT direction is wrong, distance protection must be wrong

The analog input of REL670 is connected through the transformer input module TRM, sampled by ADM, and preprocessed by SMAI. Distance protection uses three-phase current, three-phase voltage, and zero sequence quantity, and all fixed values are represented as primary values. Therefore, CT, VT ratio, and polarity settings are the basis.

CTStarPoint setting is the top cause of directional errors. REL670 regulation: Positive current and positive power indicate the flow towards the protected object, and the forward direction always points towards the protected object. If the CT star point is connected incorrectly, CTStarPoint should be set to ToObject but set to FromObject, or vice versa, the directional component will classify faults inside the area as outside the area and faults outside the area as inside the area. On site performance: no jumping due to forward direction fault, false jumping due to reverse direction fault; Or start the distance segment but lock the direction. During troubleshooting, CTStarPoint, CT ratio, and VT ratio should be checked one by one in the SMAI or TRM parameters, and compared with the CT nameplate, secondary wiring diagram, and star point grounding position inside the cabinet item by item.

The voltage circuit cannot only be checked for voltage. The secondary fuse of VT, tripping of air switch, loose terminals, reversed phase sequence, and unconnected neutral point can all cause impedance distortion in distance component measurement. The fuse failure monitoring of REL670 can detect voltage circuit faults through negative sequence or voltage/current difference algorithms, and lock the voltage dependent protection after action. If the fuse fails, the VT secondary fuse, air switch auxiliary contacts, and voltage terminals should be checked first, rather than adjusting the distance setting. Reverse voltage phase sequence can also cause errors in the selection of directional components and fault phases. A phase table should be used on site to verify the correspondence between Uab, Ubc, Uca and Ia, Ib, Ic.

CT secondary cannot open circuit, VT secondary cannot short circuit. Check the CT terminal short-circuit, the automatic short-circuit contact of the withdrawable unit, the VT secondary fuse, and the grounding. For newly put into operation or renovated intervals, a secondary injection test should be conducted to verify the starting, direction, and tripping outlet of each distance component.

Selection of Distance Components and Characteristics: Quadrilateral, Mho, and Load Intrusion

REL670 provides quadrilateral characteristic distance segments, Mho characteristic distance segments, series compensation line quadrilateral distance segments, etc. The quadrilateral characteristic is suitable for situations where independent setting of resistance and reactance ranges is required, while the Mho characteristic is suitable as a backup protection, especially in high load, multi terminal lines. When troubleshooting on site, it is necessary to first confirm which characteristic is actually in operation, and then check the corresponding set value.

Common issues with quadrilateral distance segments. ZMQPDIS is used for the first paragraph, and ZMQAPDIS is used for the second to fifth paragraphs. Each segment has positive sequence reactance X1, positive sequence resistance R1, zero sequence reactance X0, zero sequence resistance R0, phase to phase fault resistance RFPP, phase to ground fault resistance RFPE, minimum operating current IMinOpPE/IMinOpPP/IMinOpIN, etc. If there is a fault outside the area that exceeds the level, it is necessary to check whether the RFPE/RFPP is too large, whether the load intrusion characteristics have not been activated, and whether the time difference is sufficient. If the high resistance grounding fault in the area refuses to operate, check whether the RFPE is too small, whether the zero sequence compensation coefficient KN is consistent with the line parameters, and whether the minimum operating current is too high.