Can I use a multimeter to measure the quality of a motor?
Before measuring, we must first disconnect the power supply and remove the connecting piece. Assume that the upper three lines are the beginning and the lower three lines are the tail. The letters at the beginning and end indicate that it is inconvenient to type, so I named the beginning as 1, 3, and 5 and the tail as 2, 4, and 6.
Because we don’t know what the resistance between the three-phase windings is, we first set the multimeter to a certain level of electrical blocking, and finally find the appropriate level, and then make an accurate comparison.
After finding the appropriate gear, measure the resistance between the three-phase windings at the first end. If the resistance between the three-phase windings is not very different and within a reasonable range, we consider the resistance between the three-phase windings. is normal. If you are really worried, we can measure again at the end and make a comparison. This way we can make sure everything is foolproof.
Problems between three-phase windings are relatively easy to solve. It is relatively troublesome to judge the inter-turn fault of the coil.
Let’s talk about inter-turn short circuit first. The phenomenon of inter-turn short circuit is that the motor generates local heat and the three-phase current is unbalanced. When measured with a clamp meter, the direct current of the short circuit is much larger. Use a multimeter to measure the resistance at the beginning and end of the three-phase coil. The short-circuited phase should be 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, you need to use a megger. 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.
The megger is also called a megohmmeter because it is a hand-operated DC generator.
Megohmmeter, also called insulation resistance meter, is specially used to measure insulation resistance above megohm level.
Usually the industry standard is that it is normal if the insulation resistance to ground is above 0.5 megohms.
The operation is very simple. We place the insulation resistance meter flat and stable, and debug and calibrate it before measurement.
Connect the L terminal of the megohmmeter to the motor winding, and connect the E terminal to the motor casing. Measure the resistance of the 6 wires of the motor to the motor casing respectively. It is normal for the insulation resistance to be greater than or equal to 0.5 megohm, and less than 0.5 megohm. The European one is considered a leakage, and the one with a very small resistance is a short circuit.
Some friends think that you can use a megger to measure the insulation resistance of the motor coil or turns. I personally think it is inappropriate because the voltage level of the megohmmeter exceeds the withstand voltage level of the coil and may insulate the coil. breakdown.
The above method is also common for the measurement of single-phase motors. The purpose is also to determine whether there is a fault between the coils, whether there is an open circuit or short circuit inside the coil, and whether there is a short circuit or leakage to the ground.
