ABB REM54 motor terminal troubleshooting

REM54 also has a virtual simulation channel for calculating neutral current and residual voltage under the sensor scheme. Special reminder in the document: When sensitive grounding fault protection is required, it is not recommended to replace the core balanced CT with phase currents added up by numerical values. Usually, when the grounding setting value is lower than 10% of the rated value, the core balanced CT should be used. If there is a "small current grounding fault does not trip" or "frequent misoperation of grounding protection" on site, it is necessary to first confirm whether it is a dedicated zero sequence CT or a numerical calculation channel, and then check the setting value and wiring. Using three-phase summation to calculate zero sequence is prone to distortion under CT saturation, interference, or unbalanced loads, and cannot be regarded as a universal substitute.

Protection function troubleshooting: overcurrent, voltage controlled overcurrent, differential, under excitation, and low impedance

The protection function blocks of REM54 are independent of each other, with fixed value groups and data records. Typical current protection can be achieved using Rogowski coils or conventional CTs, while voltage protection can be achieved using voltage dividers or VT. When troubleshooting, it is necessary to first confirm whether the function block is activated, whether the set value group is correct, whether the measurement mode is peak or fundamental, and whether the trip output is self checked or externally locked.

Overcurrent and voltage control overcurrent. NOC3Low/High/In is used for three-stage non directional overcurrent; DOC6Row/High/In is used for directional overcurrent; VOC6Low/High is a voltage controlled overcurrent that supports voltage step, voltage slope, or input step control, and can reduce the starting current multiple at low voltages. If the motor malfunctions due to overcurrent during startup, the voltage limit, current multiplier, and startup time of VOC should be checked; If it refuses to move during a short circuit, check the starting current, time multiplier, measurement mode, and CT ratio. For directional overcurrent, it is also necessary to check the basic angle φ b, direction forward/reverse, and voltage wiring.

Differential protection. REM54 provides Diff6G stable generator differential, Diff3 high impedance or magnetic balance generator/motor differential, and REF1A high impedance restricted earth fault. The core of differential troubleshooting is CT polarity, transformation ratio, secondary wiring, and stable resistance/stable parameters. Diff6G has basic fixed values, start-up ratios, inflection points of 1/2, and transient periods; Diff3 has a basic fixed value and delay. If there is a fault differential misoperation outside the area, it should be checked whether the CT polarity is uniform, whether the differential CT has the same transformation ratio, whether the stable resistance is configured according to the calculation, and whether the secondary circuit is grounded at multiple points. If the fault in the area refuses to operate, the differential current threshold, braking characteristics, and CT saturation should be checked. High impedance differential also requires checking external stability resistors and metal oxide varistors.

Underexcitation and low impedance. UE6Row/High is under excitation protection, using impedance circle characteristics, and can set center offset, circle diameter, top distance from the R axis, and measurement mode. UI6Low/High is a three-phase low impedance protection with a Z setting of 0.01... 60 p.u., which can be used as a backup for the line. If there is an under excitation misoperation, the PT voltage, CT polarity, circular characteristic parameters, and measurement mode should be checked; If the impedance is low and refuses to move, the Z setting, phase selection, and voltage/current circuit should be checked.

Thermal overload, negative sequence, and frequency. TOL3Dev is used for thermal overload of motors, generators, and transformers, and requires selection of equipment type, starting current, allowable starting time, cold start frequency, ambient temperature, cooling/heating time constant, and restart suppression temperature. If the motor frequently trips, check whether the equipment type is selected incorrectly, whether the ambient temperature sensor is connected, and whether the time constant is consistent with the manufacturer's data. NPS3Low/High is used for negative sequence overcurrent and requires setting negative sequence startup value, time constant K, cooling time, and phase number. Freq1St1... 5 is used for underfrequency/overclocking and df/dt, and can be set with undervoltage lockout. If the frequency protection malfunctions, check whether the voltage amplitude is lower than the lockout value and whether the frequency measurement is affected by the frequency converter interference.

Power and start-up supervision. OPOW6St1... 3 is directional over power, UPOW6St1... 3 is under power/reverse power, and power direction, starting power, delay, and measurement mode need to be set. MotStart is used for motor start supervision and supports I ² t, I ² t&Tall. It can record the number of starts, allowed restart time, and locked rotor input. If the motor fails to start but the thermal protection is not activated, the starting current, allowed starting time, restart suppression, and stall signal of MotStart should be checked.