Diversified ground protection to ensure street lamp network security
With the development of urban street light
construction, most of the cement poles in the past are now replaced with metal light poles. The problem of ground protection is particularly prominent. In addition, the street light cable is mainly laid in the underground, with many contacts, which is easily affected during operation Chemical corrosion and external force damage, line short circuit and leakage faults occur from time to time, which requires us to have a perfect ground protection device
to ensure the normal operation of the street light network. In response to this need, our company has set up a street lighting network
protection QC team, which adopts multiple ground protection measures to ensure the safe operation of street lighting networks.
First, Connect all metal light pole foundations.
As we all know, grounding is divided into working grounding, protective grounding and lightning protection grounding according to its function. Metal light pole grounding is both protective grounding and lightning protection grounding. According to the regulations, "the grounding resistance of the low-voltage power equipment grounding device should not exceed 4ΩB", but it is difficult to meet this standard. For this reason, we have considered the grounding protection of metal light poles from the design stage. We put one extra wire to connect all metal light poles together. As a ground electrode, the grounding resistance of the light poles can be greatly reduced, and could meet the standard.
2, Install a leakage protector at the bottom of the metal light pole.
To this measure, colleagues have been controversial. We believe that in the street lamp 380V / 220V power supply system, when the live wire in the lamp
pole is damaged due to insulation damage and the lamp pole shell is charged, the human body's resistance and the lamp pole grounding resistance are in parallel. Once the human body contacts the lamp pole, the leakage current exceeds 50 mAh, this is very dangerous. Because the electric current flowing through the human body is very small when an electric shock occurs, it is impossible for the line protection device to operate under such a small leakage current. Therefore, relying only on the grounding of the foundation cannot absolutely guarantee safety. Install a leakage protector at the line position.
3. Install a fuse in the lamp.
Because there are many electrical components in the luminaire, in order to avoid the entire circuit trip caused by electrical failure inside a luminaire and expand the fault range, a 6A fast fuse should be installed in each luminaire. The fast-acting fuse can not only be used as overcurrent protection for lamps, but also as backup protection when the leakage protector is not operating.
4. Install "street lamp automatic control box" on the low voltage side of the street lamp transformer.
The street lamp automatic control box has over-current and over-voltage protection functions, as well as high-current ground protection function. When a ground fault occurs in the cable line, as long as the grounding current is greater than 8A, the automatic control box of the street lamp can quickly cut off the power, thereby ensuring the safety of people and equipment (32V, less than the safe voltage 36V). Here, it is important to remind that cable grounding faults often occur. Before grounding protection devices are installed, grounding cable grounding faults are generally difficult to detect. Long-term grounding currents not only consume a lot of electricity, but are also a danger. The hidden danger of the accident, I hope everyone will pay attention to it.
the metal pole bases are connected together as grounding electrodes, which greatly reduces the grounding resistance of the poles, which can provide basic guarantee for the reliable operation of the ground protection device. The installation of a leakage switch at the entrance of the metal poles can ensure personal safety; Install fast fuses in each luminaire to avoid the expansion of the fault range; install an "automatic street lamp control box" on the low-voltage side of the street lamp transformer to protect the street lamp line. At present, this scheme is adopted in the projects we are responsible for, and no electric shock has occurred, which proves that our street lamp
network ground protection measures are still perfect.