If the measured phase current is zero, the other two phase currents greatly exceed the rated current, indicating that the phase loss is running. The reason is that the circuit or the power supply is disconnected in one phase or the motor winding is disconnected. When the small motor is disconnected, it can be checked with a megohmmeter and a multimeter or a school lamp. Regardless of the motor that checks the star or delta connection, the three-phase winding connector must be disassembled to measure whether each phase is open. For medium-capacity motors, most of the windings are wound with multiple wires (multi-branch parallel). If several wires are broken or one parallel branch is disconnected, the inspection is more complicated. The three-phase current balance method and the resistance method are often used. When the difference of the three-phase current (or resistance) value is more than 5% or more, one phase with a small current (or a large resistance) is a disconnected phase.
Practice has proved that the motor open circuit fault occurs mostly at the end of the winding, at the joint or at the lead, etc., which is easier to check.
Semiconductor Fuse And Ferrite
Fuse refers to an electric appliance that, when the current exceeds the specified value, melts the fuse and disconnects the circuit with the heat generated by itself.When the current exceeds the specified value for a period of time, the fuse melts and disconnects the circuit with the heat generated by the fuse itself.A current protector made from this principle.The fuse is widely used in high and low voltage power distribution system and control system as well as power equipment.
Ferrite is a metal oxide with ferrous magnetism.As far as electrical properties are concerned, the resistivity of ferrite is much larger than that of single metal or alloy magnetic materials, and it has higher dielectric properties.Ferrite magnetic energy also shows high permeability at high frequencies.As a result, ferrite has become a non-metallic magnetic material widely used in the field of high frequency and weak current.Due to the low ferrite magnetic energy stored in the unit volume, saturated magnetic induction strength (Bs) and low (usually only pure iron 1/3 ~ 1/5), and thus limits its higher requirements in the low-frequency magnetic energy density in the field of high voltage and high power applications.
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