DC Main Line is the transmission lines of PV module system through the confluence of the bus to the inverter. If the inverter is the heart of the entire Phalanx system, then the DC trunk system is an active artery. Since the DC main system uses ungrounded scheme, if the cable grounding fault, will give the system and even equipment to bring much more harm than communication, so the PV system engineers on the DC cable is more cautious than other industry electrical engineers.

All kinds of cable accident analysis, we come to the cable grounding fault accounted for the whole cable fault 90-95%. There are three main reasons for grounding fault. First, the cable manufacturing defects for unqualified products; second, the operating environment is bad, natural aging, and suffering from external damage; third, the installation is not standard, wiring rough. The root cause of the grounding fault is only one insulating material---cable. The operating environment of the DC trunk line of PV power station is very bad. China's large-scale terrestrial power stations are generally in the West, these places are generally desert, saline and alkaline land and daytime temperature difference, rodent is also more serious, the environment will be very humid. The cable trench is buried in the laying, and the requirements for filling and digging are higher; Distributed power station cable operating environment is not better than the above ground, the cable will withstand very high temperature, there are technicians to measure and control, roof temperature can even reach 100-110 ℃ high temperature, cable fire retardant requirements, and high temperature on the insulation breakdown voltage of the cable has a great impact.

Therefore, the design of DC main cable of PV power station should consider the following points:

　　1. Insulation property of Cable

　　2, the cable moisture, cold and weather resistance

　　3. Heat-resistant and flame retardant of cable

　　4. Cable Laying mode

　　5, cable conductor material (copper core, aluminum alloy core, aluminum core)

6. Sectional specification of Cable At present, our country PV power station's direct current main cable, mostly uses the general low-voltage alternating current cable to replace, commonly used model for zr-yjv22 0.6/1kv, ZRYJY23 0.6/1kv, the cable most is the copper core cable, also some power stations gradually began to adopt the aluminum alloy conductor's cable, But the insulation material of the cable basically still presses 1KV low voltage cable standard production.

In other words, our PV system engineers are aware of the strong relationship between DC cable, but the cable technology is not too much attention.