The grounding of the DC system should include two conditions: the one-point grounding of the DC system and the two-point grounding of the DC system.
In the DC system, the DC positive and negative poles are insulated from the ground, and do not cause any harm when generating one pole grounding because there is no path that constitutes the grounding current, but it is not allowed to work for a long time on the ground of one pole, and when the other address of the same pole is grounded, it may form a signal device, relay protection or incorrect action of the control loop; After generating a little ground, and then generating another pole ground, a DC short circuit will be formed.
If the DC positive electrode is grounded, there may be a malfunction of relay protection. Since the general trip coils (such as the outlet center relay coil and the tripping and closing coils, etc.) are connected to the negative power supply, if these circuits are grounded or poorly insulated, it will cause relay protection malfunction. DC negative grounding and positive grounding are the same principle, if there is a little grounding in the circuit, it may form a relay protection rejection action, so that the incident will expand beyond the level.
The simultaneous grounding of two poles will trip or short circuit the closing circuit, which may not only blow the fuse, but also burn out the contact of the relay.
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