The judgment basis for short circuit faults is
1. Adaptive load current overcurrent sudden change method. In order to improve accuracy, it is necessary to use substation relay protection devices to determine the time width of sudden current changes 2. Quick break method. When a short circuit fault occurs in the cable line, the outgoing line protection of the substation line acts. After the switch trips, the line is cut off and the current in the line is zero 3. Overcurrent method. When a short circuit fault occurs in the circuit, the current value passing through the wire will suddenly increase. The current value is related to factors such as cable length, model, laying method, and environmental temperature
&Nbsp; Ground fault judgment basis
1. Detect the amplitude and direction of the zero sequence fundamental wave. The circuit structure with arc suppression coils is complex and unreliable, and compensation can be achieved through online monitoring and parameter adjustment. The digital fault indicator LPK2-E detects the amplitude of the zero sequence fundamental wave
2. Detects the amplitude and direction of the fifth harmonic of the zero sequence. Cannot connect when there are voltage fluctuations and non-linear loads 3. Zero sequence transient analysis method. Compensation can be achieved through online detection and parameter adjustment 4. Hand half wave method. When the direction of grounding current and load fluctuations are significant, the hand half wave method is unreliable and can be compensated through online detection and parameter adjustment 5. Transient analysis method for transient discharge of stray capacitors. The direction of transient peak current and load fluctuations are unreliable and can be compensated through online detection and parameter adjustment 6. Low resistance grounding method. When the neutral grounding method changes, zero sequence two-stage protection is used to detect grounding faults 7. Medium resistance intelligent grounding, a signal source method. By controlling the switch sequence, the neutral point is intermittently grounded through an intermediate resistor in a regular manner, thereby achieving a grounding signal and repeating the grounding process 8. High voltage pulse/low frequency current method, a signal source method. Firstly, cut off the power supply, discharge the faulty phase line with a high-voltage capacitor, or continue to apply a DC component current, and then add a low-frequency component current
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