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Technical Encyclopedia


Low-voltage protection of electrical work principle

        1.air switch,is a short circuit as long as the switch will form a loop trip switch.Circuit breaker according to its use is divided into high-voltage circuit breakers and low-voltage circuit breakers,high and low pressure line division is more fuzzy,gengrally more than 3KV called high-voltage electrical appliances.Low-voltage circuit breaker,also known as automatic switch,commonly known as “air switch”also refers to low-voltage circuit breakers,it is a manual switch function,but also automatically lose pressure,undervoltage,overload,and short circuit protection of electrical appliances.It can be used to distribute power,not frequently start the asynchronous motor,the power lines and motors and other protection,when they have a serious overload or short circuit and undervoltage failure can automatically cut off the circuit,its function is equivalent to the fuse switch and over-thermal relay,ect.combination.

       The principle of the air switch is when the line short circuit or serious overload current,the short circuit current exceeds the instantaneous trip set current value,the electromagnetic release device to produce a large enough suction,the armature suction and impact the lever,so that the hook around the axis of rotation and the lock off,the role of the reaction in the reaction of the spring under the three main contact breaking,cut off the power.
       In addition,the air switch still exists when the line occurs when the general overload,the overload current can not make the electromagnetic tripod action,but the heat element can produce a certain amount of heat,so that bimetallic heat up bending,pushing the lever to hook and lock disengage,disconnect the main contact,cut off the power supply.
       2.The thermal relay is the current through the heating element to generate heat,so that the test element heated to push the body action of a relay.Due to the thermal inertia of the heating element in the thermal relay,it can not do transient overload protection and short circuit protection in the circuit.It is mainly used for motor overload protection,phase protection and three-phase current unbalanced operation of the protection and other electrical equipment state control.
       3.The working principle of leakage protection,the normal work circuit in addition to operating current outside the leakage current through the leakage protector,then flow through the zero sequence tranfsormer(detection transformer)the same size of the current,the opposite direction,the sum of zero,transformer core in the induction flux is also equal to zero,no output secondary winding,automatic switch to keep in the state,leckage protection in normal operation.When the protection of eectical appliances and the line leakage or someone electric shock,there is a ground fault current,so that the current flow through the detection transformer and not zero,the sensor core in the induction of magnetic flux,the secondary winding induction current generated,amplified by the output,so that leakage action to promote automatic switching trip to achieve the purpose of leakage protection.
       The use of metal conductors as a melt in series,when the overload or short-circuit current through the melt,because of its own heat and fuse,thus breaking the circuit of an electrical.
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