城市照明低压配电系统接地方式探讨（Discussion on grounding mode of low voltage distribution system for urban lighting）.docVIP

城市照明低压配电系统接地方式探讨（Discussion on grounding mode of low voltage distribution system for urban lighting） Discussion on grounding mode of low voltage distribution system for urban lighting First, the common grounding way of street lamps: According to the regulation of IEC, the grounding mode of power supply system is divided into TT system, TN system and IT system. Among them, TN system is divided into TN-C, TN-S and TN-C-S systems. (1) TT mode power supply system The TT mode refers to the protective system that directly connects the metal casing of the electrical equipment, called the protective earthing system, also known as the TT system. The first symbol T said that the neutral point of power system is directly connected to the ground; second T mark indicates that the load device is not connected with the charged body exposed metal conductive part is directly connected with the earth, and how the system grounding. In the TT system, all the ground loads are called protective earthing, and the features of this power supply system are as follows. 1, when the metal casing of the electric equipment is charged (the phase line meets the shell or the equipment is damaged and the electricity is leakage), because of the earthing protection, the risk of electric shock can be greatly reduced. However, the low-voltage circuit breaker (automatic switch) does not necessarily trip, resulting in leakage of equipment of the earths surface voltage is higher than the safety voltage, belonging to the dangerous voltage. 2, when the leakage current is relatively small, even if the fuse may not be able to fuse, it also needs leakage protector for protection. 3, TT system applies to ground protection, accounting for a very scattered place. (two) TN mode power supply system; The power supply system is a protective system that connects the metal casing of the electrical equipment with the work zero line, called zero point protection system, and is represented by TN. Its features are as follows