Can a multimeter be used to measure the quality of a motor
The multimeter can measure AC voltage, DC voltage, AC current, DC current, resistance and capacitance, buzzer level, diode, etc. It also has intelligent anti burn protection design, automatic shutdown, etc. It can be said that the function is quite powerful. For an ordinary electrician, it's completely sufficient. The specific range parameters are all listed in the table, so I won't go into detail.
Can a multimeter be used to measure the quality of a motor? How should we measure it?
I think this should be viewed in two aspects. If there is a short circuit between coils, turn to turn short circuit, or open circuit, these can be measured with a multimeter. If it is a short circuit to ground or a leakage to ground, the insulation resistance value in this regard should be measured using a megohmmeter (insulation resistance meter, megger).
Let me briefly explain below: use a multimeter to measure the short circuit between motor coils, as well as the short circuit and open circuit between coil turns.
Motors can be large or small, but three-phase motors are all composed of three windings. It is essential to measure the resistance value of the three-phase winding to determine whether the motor is faulty. The resistance values of three-phase windings vary depending on the power of the motor, but their resistance values do not differ significantly, usually between 2 and 5 ohms.
Usually, three-phase motors have 6 terminals, but for some with lower power, the manufacturer has already formed a star or angle type inside the motor, and there are only three terminals in the junction box. The detection method for this type of motor is the same as the detection method for the 6 terminals, except for the short circuit between the coil turns, which ordinary electricians cannot detect.
Before measuring, we first need to disconnect the power supply and remove the connecting piece. Assuming that the top three lines are at the beginning and the bottom three lines are at the end. It is not convenient to use letters at the beginning and end to indicate typing, so I named the beginning as 1, 3, 5, and the end as 2, 4, and 6.
Because we don't know the resistance value between the three-phase windings, we first set the multimeter to a certain range of resistance, and finally find the appropriate range to make an accurate comparison.
After finding the appropriate gear, measure the resistance values between the first three phase windings separately. If the difference in resistance values between the three phase windings is not significant and within a reasonable range, we believe that the resistance values between the three phase windings are normal. I'm really not sure. We can take measurements at the end and make a comparison to ensure everything is safe.
The problem between three-phase windings is relatively easy to solve. The inter turn fault diagnosis of the coil is relatively troublesome.
Let's talk about inter turn short circuits first. The phenomenon of inter turn short circuit is that the motor is locally heated and the three-phase current is unbalanced. When measured with a clamp meter, the short-circuit current is much higher. Use a multimeter to measure the resistance values at the beginning and end of the three-phase coil, and the short-circuit phase is much smaller.
If there is an open circuit between turns, the resistance at the beginning and end of the coil winding should be infinite or very large.
If the coil is short circuited to ground or has leakage, a megohmmeter is needed. Because the voltage level of the multimeter is too low, accurate data cannot be measured.
To measure low-voltage equipment or circuits, we can choose a 500 megohmmeter.
