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The arc quenching time of a DC magnetic contactor used for DC motor control is generally longer than that of an AC magnetic contactor which crosses the zero crossing point of AC current. Many transmission & distribution device makers have made continuous efforts for smaller, lighter and more high-durable contactors with Arc extinction units having high arc extinction performance. A theory on arc quenching principle of AC and DC magnetic contactors is established in this paper. The contact area of moving and fixed contacts for contacting ports in 3 different types of arc quenching units used for DC 100 A has been computed with Holm's Equation. Electromagnetic blowout force action on the arc is analyzed using 3D finite element method (FEM) after implementing the arc model for the early stage of contact opening, Also, the breaking time for DC current of 220 V and 100 A in an arc quenching room equivalent to the FEM model has been measured. This paper presents a way for improving the arc quenching performance by comparing the electromagnetic blowout force obtained by FEM with the arc quenching time measured by an experiment and suggests a methodology for comparing and analyzing the results obtained by simulation and experiment.