Three-phase asynchronous motor open phase running fault

Lack of phase operation reason (1) the star connection broken a phase power supply.(a) as shown in figure 8,when the motor is running,for some reason,there is a phase circuit (such as W phase winding in the L3 disconnect),then in the W phase winding current,two phase winding become series relationship between rotor and stator U and V,pick up on the 380 V voltage,while two flows winding the same current,which is lack of phase operation.The motor still can continue to operate,but the work of the two phase winding,on both ends of each phase voltage is 190 v (phase voltage 220 v) in normal working conditions.Due to the phase voltage is reduced,rotating magnetic flux are reduced accordingly.But the load constant,the output torque of the motor is constant,so the stator current will increase.In addition,according to the analysis of power Angle of the normal work of the motor,three-phase winding average burden of power will increase,the winding current must be increased.In short,a phase winding,when the power is the single phase asynchronous motor burden of the remaining two phase winding.At this point in the winding current value is greater than the motor overload current,but smaller than short circuit current.

(2) delta connection broken a phase power supply.(b) as shown in figure 8,if L3 disconnect,then pick up the entire winding between two phase,which is lack of phase operation.Although the three-phase windings are working at this time,but they ac geared motor have not symmetric winding,but M phase winding facies V phase winding in series,and then winding parallel with U.In this case,the current in the winding,power is not tight and normal power current,power is different at work.Two branch current is not balanced.The theory and practice have proved that winding to delta connection,once broken a photograph,can form large circulation inside the motor winding,a very short time will burn out motor winding,the harm than y connection of motor open phase running is more serious.(3) delta connection within a phase of winding circuit.(c) as shown in figure 8,when the two phase of the motor winding form v-shaped connection,this connection,the starting torque is too small.The original ban motor starting; The motor is running,and the cut-off current is 0,is not to do work,the rest of the two phase winding load is aggravating,current increases,increased winding temperature rise.