Abstract: This paper introduces a novel AC contactor that achieves arc-free breaking, unlike conventional AC contactors. This involves applying power electronic devices such as thyristor modules and optoelectronic devices to the main and control circuits of the AC contactor to achieve arc-free breaking. The design, working principle, design analysis, and conclusions of this novel AC contactor are presented. Keywords: AC contactor; electric arc; arc-free breaking 1 Overview This paper focuses on a novel AC contactor capable of arc-free breaking. Contactors are among the most widely used low-voltage electrical appliances operating on a long-term duty basis. However, conventional AC contactors have drawbacks in their contact arc-extinguishing systems (moving and stationary contacts and arc-extinguishing chambers, etc.) that cannot be overcome by conventional designs. When interrupting circuit current, the contacts inevitably generate an electric arc. The reason why the electrical life of AC contactors is far lower than their mechanical life is mainly due to the presence of the arc during the breaking process. Previous research has also yielded many results in the areas of powerful arc extinguishing and arc-free breaking. However, due to reliability, cost, and complexity of solutions, there are few commercially available finished products. Based on the above problems, this paper proposes a simple, reliable, low-cost, and high-performance solution for contact arc extinguishing systems. This solution retains the advantages of the original contactor, eliminates the sparks and arcs generated during switching, overcomes its pollution of the power grid and interference with radio waves, avoids overvoltage surges caused by inductive loads during disconnection, increases the operating frequency of the AC contactor, and extends its lifespan by tens of times. It provides highly reliable components for various electronic control systems and power distribution systems. The working principles, design analysis, and experimental conclusions are described in detail, and a prototype is already in operation. 2. Working Principle of Arc-Free Breaking With the continuous advancement of low-voltage electrical technology, the mechanical life of AC contactors has reached over 10-15 million cycles, while their electrical life is only about one-tenth of their mechanical life. This is mainly due to the erosion of the contacts by electric arcs. Traditional methods generally improve arc-extinguishing capabilities, but none can completely eliminate the arc, thus failing to achieve arc-free breaking. This method uses power electronic devices connected in parallel with the contactor's main contacts. A simple and reliable control circuit precisely controls the on and off times of the thyristor to match the inherent on and off times of the contactor, achieving contactless switching of the main circuit, i.e., arc-free switching. Simultaneously, during the normal operation of the main circuit, the thyristor in the power electronic device does not operate; the contactor contacts maintain the circuit's connection. This overcomes the poor surge current resistance of simply using contactless switches. Its working principle is shown in Figure 1. Taking the CJ20-315A AC contactor as an example, each phase contact of the AC contactor in the diagram is connected in parallel with a bidirectional thyristor module. The inherent operating parameters of the contactor are: pull-in time 18ms, release time 12ms. The trigger control circuit in the diagram is energized and de-energized simultaneously with the contactor coil. When the contactor coil is energized, the trigger control circuit can provide a trigger signal 10ms after energization, causing the three pairs of bidirectional thyristors to conduct instantaneously. After 8ms, i.e., 18ms, the three pairs of normally open contacts of the contactor close. At this time, although a trigger signal is still applied to the trigger terminal of the thyristor, the thyristor is in a non-working state because the closed contacts of the contactor short-circuit the anode and cathode of the thyristor. That is, the thyristor only works for a few milliseconds at the moment the circuit is turned on, and the subsequent circuit connection is completed by the contactor contacts. When the contactor wants to disconnect the circuit, i.e., when the contactor coil is de-energized, before the contactor contacts are fully open... Due to the sharp increase in contact resistance between the contacts, the voltage drop across the contacts also rises sharply. When this voltage drop reaches only about 8-10V, the trigger control circuit in the diagram can continuously provide a trigger signal for 15ms after power failure (relying on capacitor energy storage). Thus, when the voltage drop across the thyristor connected in parallel with the contacts reaches 8-12V, it is sufficient to make the thyristor switch to the conducting state. As the contactor contacts are about to open, the current flowing through the contacts is transferred to the thyristor connected in parallel, which has already become the conducting state, due to the sharp increase in contact resistance. At 12ms, the contactor contacts open first. Since almost no current flows through the contacts (the current has almost all been transferred to the thyristor), no arc is generated when opening. After 3ms, i.e., at 15ms, the trigger control circuit stops providing a trigger signal, and the thyristor is cut off, thereby realizing arc-free circuit interruption. This achieves arc-free circuit interruption. The above arc-free breaking scheme has passed mechanical and electrical life tests on the prototype, demonstrating outstanding safety, reliability, and ease of implementation. Applying it to widely used ordinary contactors can bring about a revolutionary change. 3. Process Implementation Considering that the existing ordinary contactor process is basically stable, only a simple modification to its electromagnetic 5-contact arc-extinguishing system is needed to achieve arc-free breaking. For the contact arc-extinguishing system, since arc-free breaking has been achieved, the arc-extinguishing cover loses its original function and can be replaced by a shell made of high-temperature resistant insulating material. The space inside the shell perfectly accommodates the three bidirectional thyristors and their control circuits, ensuring that the modified contactor has the same external dimensions as the original contactor, and that all external characteristics, such as wiring, remain unchanged. This is highly beneficial for the large-scale promotion and use of this technology. 4. Conclusion Applying power electronic devices to the contactor field, and using bidirectional thyristors connected in parallel with the contactor contacts in the contact arc-extinguishing system, allows for arc-free switching of the circuit during both connection and disconnection through a specific control circuit. This new method reduces electrical wear of the contacts when the contactor breaks the circuit, significantly improving the electrical life of the AC contactor. Furthermore, because it achieves arc-free disconnection, it can be widely used in flammable and explosive environments such as petrochemical mines. 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