Can I use a multimeter to measure the quality of the motor?
I think we need to look at this from two aspects. If there is a short circuit between coils, a short circuit between turns, or an open circuit, these can be measured with a multimeter. If it is a ground short circuit or ground leakage, the insulation resistance value in this regard should be measured with a megohmmeter (insulation resistance meter, shake meter).
Let me briefly explain how to use a multimeter to measure short circuits between motor coils, as well as short circuits and open circuits between coil turns.
Motors come in different sizes, but three-phase motors are composed of three windings. It is essential to measure the resistance of the three-phase winding to determine whether the motor is faulty. The resistance value of the three-phase winding varies depending on the power of the motor, but their difference in resistance value is not very large, generally between 2-5 ohms.
Usually, three-phase motors have 6 terminal posts, but for some smaller power motors, manufacturers have already formed star or angle shapes inside the motor, and there are only three terminal posts in the junction box. The testing method for this type of motor is the same as the testing method for six terminal posts, except that there is a short circuit between the coil turns, which ordinary electricians cannot detect.
We need to disconnect the power supply and remove the connecting piece before measuring. Assuming the top three lines are at the beginning and the bottom three lines are at the end. Using letters at the beginning and end to indicate typing is inconvenient, so I named the beginning 1, 3, 5 and the end 2, 4, 6.
Because we don't know the resistance between the three-phase windings, we first set the multimeter to a certain resistance level, then find the appropriate level and make an accurate comparison.
After finding the appropriate gear, measure the resistance values between the three-phase windings at the head end. If the difference in resistance values between the three-phase windings is not significant and within a reasonable range, we consider the resistance values between the three-phase windings to be normal. If you're really worried, we can measure again at the end and make a comparison, which can ensure that everything is foolproof.
The problem between three-phase windings is relatively easy to solve. The diagnosis of inter turn faults in coils is relatively more complicated.
Let's talk about inter turn short circuits first. The phenomenon of inter turn short circuit is that the motor heats up locally and the three-phase current is unbalanced. When measured with a clamp meter, the current in the direction of the short circuit is much larger. Use a multimeter to measure the resistance values at the beginning and end of the three-phase coils separately. The short circuited phase is much smaller.
