What is the reason for measuring three-phase resistance balance with a multimeter
The three-phase water pump may have some leakage when measured with a megohmmeter. To be precise, it should have been shaken with a megohmmeter during a power outage, which means poor insulation. The insulation between certain parts of the cable or motor and the casing is poor. But the coil of the motor itself is not a problem. So it's good for you to measure the three-phase resistance with a multimeter. This is not contradictory. Find and handle the areas with poor insulation. That's it.
I will only talk about the handling methods in practical work. Generally, a 500 volt megohmmeter is used to measure the insulation resistance of the coil and the casing. There are three results: one is that the resistance value is zero. As the saying goes, if the casing is touched, it means that the motor is broken. The second is that the resistance value is infinitely large, indicating that the motor is good. The third is that there is a resistance value, indicating that there is an insulation problem. Based on my experience, if the insulation resistance value is greater than 0.5 megaohms, it can still be used, but if it is less than 0.5 megaohms, it cannot be used. The second issue is to use a multimeter to measure the balance of three-phase resistance, which is not possible. The reason is that the short circuit between the turns of the motor coil cannot be measured. In my experience, even good motors do not have exactly the same resistance value. Some high-power motors have thick coils, and the resistance value you measured is zero ohms, which cannot indicate the problem. When you look at three-phase balance, it can only be seen that the motor is starting and running. Take a card to check the three-phase current, and you will know whether it is normal or not.
If you use a megohmmeter to measure the resistance between the three-phase coils without disconnecting them, it means that you don't understand the common sense of the instrument at all. It's better not to play with it. If a megohmmeter measures the resistance between the three-phase coil and the casing, and a multimeter measures the resistance between the coils, it indicates that the water pump is heating up and causing insulation aging, and the coil winding needs to be replaced! I think you should be in the latter situation.
