Electromotor is us the most commonly used a kind of equipment, no matter be industry,production or daily life electromotor always appear beside us. Electromotor differs according to power source normally cent is dc motive and AC motor, the electromotor in power system is alternating current machine for the most part, but synchronous electric machinery or asynchronous electric machinery.

When we are using motor, we must carry resistor, resistor and electromotor can say is along with the shadow travel. When electromotor is used resistor has the effect of current limliting of good to step-down specified number in circuit normally, in order to ensure electric machinery moves normally, resistor is linked below the principle of the step-down in electromotor and current limliting.

Use in electromotor above all in use resistor series connection to undertake step-down starts control circuit commonly, string together a certain quantity of resistor in electromotor stator circuit namely. Electromotor is in when starting, use the function that step-down, current limliting goes to since the resistor that strings together, start when electromotor after ending, repass circuit receives the resistor weak point of series connection, make electromotor enters total pressure to run state normally.

Through the following we can understand, in stringing together the control circuit that resistor starts in electromotor step-down, whole moving process includes step-down to start, total pressure moves and stop machine 3 processes. It is better that in this process a lot of circuits design personnel to be able to use means of resistor series connection to come normally the step-down that undertakes electromotor and current limliting action.