Motor using frequency converter leakage after what should I do?

by:J&T     2020-06-30
Motor type many, the use of occasions is very broad, now live in production, the use of the motor are common, ordinary motor, explosion-proof, frequency conversion, and so on, the motor installed in use is often the frequency converter, the motor with frequency converter in the leakage? Some field using inverter control motor, can appear the leakage problem, dozens of creepage voltage v to two hundred v voltage range. Aimed at this problem, this paper analyzes the causes of this kind of phenomenon is as follows: one, the influence factors of leakage current size are: 1, the leakage current cable leakage circuit breakers, filter the leakage current of cable length. The leakage current of frequency converter, motor cable length. 2, the leakage current of the motor. 3, filter leakage current ( Including frequency converter) 。 Second, the inverter output PWM ( Pulse width modulation, similar to a high-speed switch) Mode control, so the high frequency leakage current will happen. Three level before the inverter, power supply transformer, motor drive equipment of PE point must be together, after reunification to ground. The inverter is high frequency square wave voltage output, because inside the motor coil and equivalent capacitance exists between the motor shell, the resulting leakage current. If no grounding or bad, there will be a leakage phenomenon. Due to the asynchronous motor, motor shell will be induced voltage ( The so-called leakage) , so, the motor manufacturer at the time of the motor factory, install grounding terminals in the junction box, convenient user to connect the earth when applied to eliminate the induced electromotive force ( Eliminate voltage induced leakage) To solve human exposure is the feeling of electric motor. Run the motor, power frequency switching frequency is approximately 50 hz, power frequency is very low, so in general will not have the feeling of leakage (almost Unless the motor insulation is very poor) 。 And the inverter control, due to its switching frequency is much higher than the work frequency, so the frequency inverter to control motor rotation, motor shell will have the feeling of the leakage. Three, according to the function block diagram, the inverter control motor running after three-phase power converter rectifier bridge rectifier, the capacitor filter to inverter bridge ( IGBT) Bridge, through the inverter output frequency and voltage adjustable three phase alternating current (ac) to control the operation of the machine. Three mutually sent 120 degrees alternating current flowing in the three-phase stator coil winding of the motor, to produce a rotating magnetic field, make the rotor on the stator winding of the motor automatically under the effect of rotating magnetic field is rotating. After the three-phase motor stator winding through the current produce a rotating magnetic field, and according to the principle of electromagnetic induction, the shell of the motor can produce inductive electromotive force. The induced electromotive force size, depends on the size of the switch frequency of inverter IGBT and C× DV / DT ( Related to the speed of IGBT switch) 。 If the induction electromotive force is bigger, so people touch will feel being shocked. In theory of the IGBT switching frequency is higher, the effective value of motor shell induced electromotive force ( The induced voltage) The higher, and the control precision and dynamic response of the frequency converter for motor is higher, after the body touch the greater is the feeling of electric; On the other hand, the IGBT switching frequency is lower, the effective value of motor shell of induction electromotive force ( Induced voltage) After the lower, and from the body touch is the feeling of power.
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