1. The two-point grounding protection device for the stator and rotor excitation circuits is used to monitor the situation where the rotor circuit of the running generator has a permanent metallic grounding. Once the second point of grounding occurs, a signal will be generated or the generator switch (i.e., the excitation switch) will be disconnected to extinguish the magnetizing current.
2. During normal operation of the generator, the two-point grounding protection for the excitation circuit is not activated. Only the 1DK, 2DK, 3DK, and 4DK circuit breakers are closed and the 1LP and 2LP pressure plates are properly pressed, and the QP pressure plate is set to the signal position.
3. The insulation monitoring voltage meter measures the voltage values of the positive and negative to ground once per shift and calculates the insulation value.
4. Under the following circumstances, this protection device should be put into operation:
(1) The rotor grounding fault of the generator is a permanent metallic grounding (with a grounding resistance less than 100 ohms).
(2) The one-point grounding fault does not occur in the excitation circuit.
5. The procedure for putting the protection device into operation is as follows:
(1) Close the 5DK circuit breaker.
(2) Press the button, adjust the regulator potentiometer, and make the voltage meter indicate zero.
(3) According to the operating conditions, allow the magnetic field resistance to be adjusted several times. Each time, press the button to check the voltage meter reading. If the reading keeps changing, it indicates that the grounding has occurred in the magnetic field circuit of the exciter, and the protection device should not be put into operation. Instead, enhanced monitoring should be carried out and the generator should be shut down for inspection.
(4) If the magnetic field resistance is adjusted several times according to the above circumstances and the voltage meter reading remains zero, it indicates that there is one-point grounding on the rotor. Then close the 6DK and 7DK circuit breakers, and the protection device will be put into operation.
(5) After the protection device is put into operation, the handwheel of the potentiometer is prohibited from being moved, and attention should be paid to checking for overheating.
(6) When the two-point grounding protection device operates, if there are no abnormal indications on the generator’s various meters, check if the potentiometer has moved from its original position. If it has, re-adjust the balance. If it is confirmed that there is two-point grounding, follow the accident handling procedures.
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Post time: Apr-10-2026