Switch type comparison project AC contactor composite switch phase selection switch system operation cost has arc, high surge current and switching overvoltage, compensation capacitor is easy to breakdown, need frequent maintenance and replacement, long-term operation cost is high. Single contact magnetic retention structure, short mechanical and electrical life, thyristor is easy to damage, it is not easy to check the burn out of contact, long-term operation cost is high. No arc, long service life of compensation capacitor, single contact magnetic holding structure, no thyristor element, low failure rate and low long-term operation cost. When the control voltage is low or high, the coil is easy to burn, which can lead to the breakdown of the capacitor and the tripping of the main switch, resulting in poor safety and stability. The thyristor is sensitive to the change rate of voltage, has weak ability to withstand the over-current, has hidden trouble of breakdown, and the safety and stability are still weak. The microprocessor is used to drive the magnetic holding relay to control the contact, and the thyristor is no longer used. The danger caused by the breakdown of the thyristor is eliminated, and the safety and stability are greatly improved. The product has low cost, moderate inrush current, no detection of voltage zero crossing, inrush current more than 20 times voltage zero crossing trigger no inrush current voltage zero crossing, no detection of current zero crossing, arc strong current zero crossing cut off, no arc current zero crossing cut off, no arc overload capacity is poor, strong control system is simple and complex, keep working noise small The power supply is polluted, there is harmonic pollution at the moment of starting and breaking, there is no driving power consumption, 10w-100w, 3-10W, 1-3W. The reliability only plays the role of switch, and there is no protection function. There are open phase protection, switch not in place protection, with self diagnosis fault protection, power supply voltage open phase protection, power failure protection and other functions. The service life of the compensation capacitor is shorter than that of the rated contact, about 10000 times to tens of thousands of times. The contact life and mechanical life are about several hundred thousand times. The thyristor works for a long time, needs high voltage and is easy to be damaged. Contact life and mechanical life can reach one million times, long service life, weak and very strong anti harmonic ability, weak and strong anti-interference ability, operating frequency 100 to 1000 times per hour, dozens to 100 times per hour, 100 to 1000 times per hour, application voltage level 400V, 400V, 400V relay can be used, high voltage circuit breaker can be used to drive AC coil Thyristor driven DC coil magnetic holding relay microprocessor driven DC coil magnetic holding relay contact structure bridge structure mechanical relay single contact structure mechanical semiconductor parallel relay single contact structure mechanical thyristor pressure line voltage——