Can you measure the quality of the motor with a multimeter?
This multimeter can measure AC voltage, DC voltage, AC current, DC current, resistance and capacitance, buzzer gear, diode, etc., and 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 is completely enough. The specific range parameters are all on the table, so I won't go into details.
So can you measure the quality of the motor with a multimeter? How to measure it?
I think this should be viewed from two aspects. If it is short circuit between coils, turn-to-turn short circuit and open circuit, these can be measured by multimeter. If it is a short circuit to the ground and leakage to the ground, the insulation resistance value in this respect should be megohmmeter (insulation resistance meter, shaking table).
Briefly, use multimeter to measure the short circuit between motor coils and the short circuit and open circuit between coil turns.
There are large and small motors, but all three-phase motors are composed of three windings. It is necessary to measure the resistance of three-phase winding to judge whether the motor is faulty. The resistance of the three-phase winding varies according to the power of the motor, but their resistance is not very different, generally between 2 and 5 ohms.
Usually, three-phase motors have six terminals, but for some low-power motors, manufacturers have formed star-shaped or angle-shaped motors, and there are only three terminals in the junction box. The detection method of this kind of motor is the same as that of six terminals, except that the coil turns are short-circuited, so we ordinary electricians can't detect it.
Before measuring, we must first disconnect the power supply and remove the connecting piece. Assume that the top three lines are the head end and the bottom three lines are the tail end. Letters at the beginning and end indicate that typing is inconvenient, so I named the first end as 1, 3, 5, and the last end as 2, 4, 6.
Because we don't know the resistance between the three-phase windings, we first hit the multimeter to a certain gear of the electric block, and finally find the appropriate gear, and then make an accurate comparison.
After finding a suitable gear, measure the resistance values between the three-phase windings at the first end respectively. If the resistance values between the three-phase windings are not much different and within a reasonable range, we think that the resistance values between the three-phase windings are normal. I really don't trust you. We can take another measurement at the end and make a comparison, so as to be sure.
The problems between three-phase windings are relatively easy to solve. It is relatively troublesome to judge the turn-to-turn fault of the coil.
Let's talk about turn-to-turn short circuit first. The phenomenon of turn-to-turn short circuit is that the motor is locally heated and the three-phase current is unbalanced. Measured with a clamp meter, the direct current of short circuit is much larger. Use a multimeter to measure the resistance of the head and tail ends of the three-phase coil, and the short-circuited phase is much smaller.
If the turn-to-turn circuit is open, the resistance at the beginning and end of the coil winding should be infinite or very large.
If the coil is short-circuited to the ground or leaks electricity, you need to use a megohmmeter. Because the voltage level of the multimeter is too low, it is impossible to measure accurate data.
To measure low-voltage equipment or lines, we can choose a 500 megger.
Megohmmeter is also called shaking table because it is a hand-operated DC generator.
Megohmmeter, also called insulation resistance meter, is specially used to measure insulation resistance above megohmmeter level.
Usually, the industry standard is that the insulation resistance to the ground is above 0.5 megohm, which is normal.
The operation is very simple. We can only measure the insulation resistance meter after it is leveled and stabilized and adjusted.
Connect the L terminal of megohmmeter to the motor winding, and connect the E terminal to the motor housing, and measure the resistance of the six motor terminals to the motor housing respectively. The insulation resistance is normal if it is greater than or equal to 0.5 megohmmeter, and it is considered as leakage if it is less than 0.5 megohmmeter, and it is short circuit if the resistance is very small.
Some friends think that megohmmeter can be used to measure the insulation resistance of motor coil or turn-to-turn. Personally, I think it is inappropriate, because the voltage level of megohmmeter exceeds the withstand voltage level of coil, which may break down the insulation of coil.
The measurement of single-phase motor also uses the above method. The purpose is also to judge whether there is a fault between coils, whether there is open circuit and short circuit inside coils, and whether there is short circuit and leakage to ground.
