Street Lighting systems, usually installed outdoors, are extremely threatened by lightning strikes. It can cause damage to the street lights, or cause fire or casualties, resulting in huge losses. Therefore, systems with greater risk of lightning strikes usually need to install effective lightning protection devices or add front-level lightning protection circuits. Taking street lamp systems as an example, we will focus on the impact of lightning protection installation differences on lightning protection effects.
1. The basic structure of the intelligent street light system
Modern intelligent street lamp systems mainly include lightning protection devices, LED street lamp power supplies, street lamp LEDs, switch relays, intelligent control systems, system power supply AC-DC modules, etc. The framework diagram is shown in Figure 1.
Figure 1 Schematic diagram of intelligent street light system
2. Surge test comparison of different wiring
Figure 1 shows the wiring structure of the two lightning arresters. The picture on the left shows the mains input first through the device and then to the lightning arrester. The picture on the right shows the input mains passing the lightning arrester first and then to the subsequent equipment, and the input wiring of the lightning arrester is short. The wiring of the input lightning protection device on the left is longer, which is equivalent to connecting the lead inductance, as shown in Figure 2.
Figure 2 Schematic diagram of intelligent street light system
3. Analysis of surge test results
If the lightning protection requirement of the power port of the system is 30kA in differential mode, a nominal 30kA lightning protection device is connected in parallel to the power port of the system. In the actual test, connect according to the left picture of Figure 1, the LED drive power supply and the AC-DC module of the rear stage are damaged, but the lightning protector is intact; and if connected in the order on the right, the lightning protector and the rear module are normal.
As shown in Figure 2, in the differential mode test, the surge current flows in the direction of the arrow. Due to the long wiring, the total length of the wiring between the lightning arrester and the device port is 0.5m, and the cable inductance is about 0.5uH. Under the impact of 30kA surge current, the cable voltage drop is about: U=L*di/dt=0.5 uH*30kA/8us=1875V. Coupled with the residual voltage of the lightning arrester itself of about 1500V, the total surge voltage applied to the device port on the left is as high as 3375V. However, ordinary AC-DC power modules are difficult to withstand surges above 3000V without adding peripheral circuits. Therefore, the wrong wiring will eventually cause the lightning arrester to lose its protection under the impact of high-energy surges.
The wiring structure on the right side is not the case. The input surge impact first passes through the lightning arrester, and finally the surge voltage reaching the input end of the subsequent equipment is only the residual voltage of the lightning arrester: 1500V, and the equipment is well protected.
4. Points for the correct application of lightning protection devices
The input wiring of the lightning protector should be as short and thick as possible, and if necessary, multiple strands are connected in parallel to reduce the self-inductance of the wire, so that the lightning protector can absorb the surge impact energy of the input end as much as possible;
The protected equipment needs to be installed after the lightning protector, so that the input surge impact is attenuated by the lightning protector and then enters the rear stage for protection;
Reduce the parallel distance between the input wiring of the downstream equipment and the input line without lightning protection, and reduce the possible surge coupling path;
The wiring of the lightning arrester for the signal link is similar and follows the same principle.
SHENZHEN CHONDEKUAI TECHNOLOGY CO.LTD , https://www.szfourinone.com