About DC leakage current protection measures
Leakage current protection is an effective means to monitor the insulation status of electrical system in real time, and is one of the ways to protect the safety of operators and systems. Electrical designers in the design of system solutions, the correct and reasonable design protection scheme can not be ignored.
In the AC power supply system, due to the working grounding of the neutral point of the transformer in the general power supply system and the existence of a large distributed capacitance between the power grid and the ground, when the insulation drops or the insulation is damaged, the power supply and the ground form an effective loop current (leakage current), and the leakage current protection device protects the system. The current monitoring is generally designed in the power switch, or in the circuit design leakage current relay, and the protection action setting value can be freely adjusted in a certain range. The technology is already mature and widely used in practical solutions, which will not be detailed here.
For DC power supply systems, in general, the loop is relatively single, the network distribution capacitance is small, and the ground is almost isolated. When the ground insulation failure occurs in the system, the power supply cannot form an effective loop current with the ground. At this time, the system can not detect the fault signal, which requires the design of leakage current detection circuit, to achieve reliable protection.
In the low voltage DC circuit, due to the low voltage, the negative electrode of the power supply can be directly connected to the ground to play a circuit protection role.
In the DC system with high voltage, multi-loop and complex system. Generally designed to connect a high resistance value resistor (greater than or equal to the industry insulation resistance standard) between the power supply and the ground to establish an organic connection with the ground, the form of monitoring sampling signal can be a voltage or current signal.