What Kind Of Backup Protection Device Should Be Used For Surge Protector?
With the release of GB51348, surge protectors have been widely used, but photovoltaic DC surge protectors SPD still use GR or GPV fuses (Fuse) as backup protection devices. The purpose is to cut off the power supply through the Fuse to prevent the SPD from catching fire when the SPD fails due to short circuit unexpectedly and its own disconnection device cannot be disconnected from the grid.
The following three conditions must be met to select a photovoltaic DC surge backup protection device:
When normal lightning current passes through the SPD, the backup protection device cannot operate, ensuring the smooth flow of the lightning protection branch, and the lightning current can be smoothly discharged into the ground through the surge protector.
When a short circuit fault occurs in the SPD, the backup protection device must act immediately to quickly cut off the lightning protection branch to ensure that the SPD does not catch fire.
Ensure that the previous level Fuse or circuit breaker in the line does not operate and does not cut off the power supply to maintain the continuity of power supply.
The Imax of the DC surge protector commonly used in photovoltaics is 40kA. The recommended fuse capacity in series at the front end of the 40kA DC surge protector should be 125A (because 125A can pass the 40kA test). The fuse must be able to withstand the expected lightning current impact without melting.
According to the standard requirements of the fuse, it is qualified if it does not operate for 5s at 5 times (625A) the rated current (125A). Even if the SPD fails in a short circuit, as long as the short-circuit current is not greater than 125A, even if the SPD catches fire, the fuse will not melt. In fact, under the test condition of 10A, the SPD caught fire in about 10s (tested by releasing the SPD's own disconnection device), which is obviously mismatched.
In actual use, only when the expected short-circuit current at the installation site of the SPD (assuming that it is the current generated by the SPD short circuit) is far greater than 125A, such as more than 10 times the rated current (1250A), the fuse connected in series at the front end of the SPD can be normally fused and play an effective protective role.
However, the photovoltaic system cannot meet this current requirement, so the fuse (Fuse) connected in series at the front end of the photovoltaic DC surge protector SPD as its backup protection device cannot completely solve the safety problems caused by SPD failure short circuit!
The circuit breaker type backup protector on the market cannot meet the high DC voltage protection requirements of the photovoltaic DC SPD, so it cannot be used in the photovoltaic industry. At present, some companies are developing fuse type backup protectors. We believe that with the development of technology, this problem can be overcome!
