Other factors affecting the distribution of the surge protector: a reduction in the grounding resistance of the transformer end will increase the current distributed in the electron line. An increase in the length of the power supply cable will reduce the current distributed in the power line and result in a balanced current distribution among the several conductors. Too short cable lengths and too low neutral impedance will cause current imbalance, causing differential mode interference. When the power supply cable is connected to multiple users, the effective impedance is reduced, and the distribution current is increased. In the continuous power supply state, the temporary flow of the lightning mainly flows into the power line, which is the reason why most lightning losses occur at the power line. The power line should realize multi-level protection.
The multi-level protection is based on each lightning protection zone. The lightning energy is gradually weakened, so that the limiting voltages of the various levels are matched with each other, and finally the overvoltage value is limited to the insulation strength of the equipment. Multi-level protection becomes necessary in the following cases: a certain level of lightning arrester fails or a certain lightning protection device fails. The residual voltage of the lightning arrester does not match the insulation strength of the equipment, and the cable has a long length in the building.