Different systems are applied. The direct current surge protector is used in DC systems. AC surge protectors are used in AC systems.
The biggest difference between AC and DC systems is the frequency, the cycle change of 50Hz of the AC system forms three important nodes of zero, positive peak and negative peak (peak valley), so that the SPD takes turns to bear the voltage of the positive peak and the negative peak in the positive and negative directions, plus the positive and negative peak voltage amplitude, the cycle time is symmetrical, so that the positive and negative electron arrangements in the SPD chip are also equal, and are in a relatively stable state.
DC system has no frequency, its comprehensive impedance is less than the last two terms of the above formula (only the internal resistance and line resistance of the power supply itself), so the DC system is lower than the internal resistance of the AC system, the advantage of low DC internal resistance is that the efficiency is very high, the disadvantage is that once the short circuit, the discharge current will be very large, plus because there is no zero-crossing characteristics, it is difficult to cut off, it is easy to cause fire accidents, and this fire is difficult to control, often to exhaust the energy in it will stop. Therefore, in the power supply system, the price of direct current surge protector, DC circuit breaker, and DC relay is higher than that of similar products in AC systems, which is also because of the difficulty of DC breaking, high production process, high technical requirements, and high cost.